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  • Electronic Resource  (236)
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  • 1991  (236)
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  • MRI
  • 1
    Electronic Resource
    Electronic Resource
    MRI of knee arthritis in rheumatoid arthritis and spondylarthropathies (1991)
    Springer
    Rheumatology international 11 (1991), S. 183-186 
    Details
    ISSN: 1437-160X
    Keywords: MRI ; Rheumatoid arthritis ; Spondyl-arthropathy ; Gonarthritis ; Arthritis ; Radiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The knees of fifty-two patients suffering from rheumatoid arthritis (RA), 22 patients with seronegative spondylarthopathies (SA) as well as of 20 healthy volunteers were examined by magnetic resonance imaging (MRI). Osseous erosions (RA 52%-SA 18%; P〈0.005), Baker cysts (RA 56%-SA 12%; P〈0.005), pannus formation (RA 67%-SA 36%; P〈0.05), and cartilage thinning with narrowing of the joint space (RA 46%-SA 18%; P〈0.05) proved to be more frequent MRI findings in patients with RA. Additionally, in patients with RA erosions were more extensive. Follow-up MRI examinations of 19 patients revealed an improvment in MRI changes in SA within an average interval of 6 months. No substantial changes were noted in 7 of 13 RA patients. Quantitative and qualitative MRI findings of knee arthritis differ in patients with RA and SA and this was statistically significant. However, as there is considerable overlap of the MRI and radiographic changes in both groups the discriminating diagnostic value in the individual case was limited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332559
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  • 2
    Electronic Resource
    Electronic Resource
    MRI of trigeminal neuralgia: Initial clinical results in patients with vascular compression of the trigeminal nerve (1991)
    Springer
    Neurosurgical review 14 (1991), S. 69-73 
    Details
    ISSN: 1437-2320
    Keywords: Basilar arteries ; cerebellar arteries ; MRI ; trigeminal nerves ; trigeminal neuralgia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The most common cause of the idiopathic trigeminal neuralgia are tortuous arteries in the prepontine space. The trigeminal nerve can be compressed by the superior cerebellar artery, the inferior cerebellar artery, or the basilar artery. Seldom the nerve is traumatised by an enlarged vein. Because an operative decompression of the nerve can relieve pain, a preoperative evaluation is needed. Angiography of the vertebral arteries is able to predict a tortuous artery close to the trigeminal nerve but cannot show the nerve itself. MRI can show tortuous vessels and the trigeminal nerve together on one single image by means of a 3D gradient-echo FLASH sequence with an effective slice thickness of approximately 1 mm and secondary reconstructions in every desired plane. MRI thus provides an efficient tool for the evaluation of patients with trigeminal neuralgia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338197
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  • 3
    Electronic Resource
    Electronic Resource
    High-resolution magnetic resonance imaging of the interphalangeal joints of the hand (1991)
    Springer
    Skeletal radiology 20 (1991), S. 273-277 
    Details
    ISSN: 1432-2161
    Keywords: High-resolution magnetic resonance imaging (MRI) of finger joints ; MRI ; Arthritis ; Osteoarthritis ; Hand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract High-resolution magnetic resonance imaging (MRI) of the interphalangeal joints of the fingers is being employed to study arthritis. To facilitate this research, a clear understanding of the structures visualisable by MRI is necessary. A gradient echo (GE) sequence was developed that produced good contrast between cartilage and other joint structures. These detailed images, with an in-plane resolution of 200 × 100 μm, enable resolution of three cartilage zones which can be interpreted as a superficial layer at the cartilage/cartilage interface, an intermediate layer and calcified cartilage in contact with bone; these correlate well with known anatomy. Further analysis of the images indicates that although a chemical shift artifact causes changes in the images at the field strength used (0.5 T), it does not cause enough distortion to necessitate suppression of the effect. Furthermore, the only detectable susceptibility artifact at these low field strengths was a loss of signal in bone trabeculae at the bone/cartilage interface. There is clearly potential in the study of the articular structures, in particular cartilage, in detail, using high-resolution MRI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02341664
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  • 4
    Electronic Resource
    Electronic Resource
    Evaluation of Blalock-Taussig shunts in newborns: value of oblique MRI planes (1991)
    Springer
    The international journal of cardiovascular imaging 7 (1991), S. 1-5 
    Details
    ISSN: 1573-0743
    Keywords: newborns ; MRI ; congenital heart disease ; systemic shunts ; oblique views
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Eight infants with systemic-pulmonary Blalock-Taussig shunts were evaluated by spin-echo ECG-gated MRI. Contrary to Echocardiography, MRI using coronal oblique projections successfully visualized all palliative shunts entirely in one single plane (including one carried out on a right aberrant subclavian artery). MRI allowed assessment of size, course and patency of the shunt, including pulmonary and subclavian insertion. The proximal portion of the pulmonary and subclavian arteries were also visualized. We conclude that MRI with axial scans completed by coronal oblique planes is a promising, non invasive method for imaging the anatomical features of Blalock-Taussig shunts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01797675
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  • 5
    Electronic Resource
    Electronic Resource
    The neuropathology of developmental dysphasia: Behavioral, morphological, and physiological evidence for a pervasive temporal processing disorder (1991)
    Springer
    Reading and writing 3 (1991), S. 363-377 
    Details
    ISSN: 1573-0905
    Keywords: developmental dysphasia ; dyslexia ; temporal processing ; MRI ; thalamic nuclei ; caudate nuclei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Education
    Notes: Abstract Over the past twenty years, Tallal and colleagues have directed their research toward defining the neuropathological mechanisms responsible for developmental dysphasia. We have hypothesized that higher level auditory processing dysfunction, which has previously been associated with developmental dysphasia, may result from more basic temporal processing deficits which interfere with the resolution of rapidly presented, brief duration stimuli. This temporal processing deficit interferes with adequate perception of specific verbal stimuli which require resolution of brief duration formant transitions, resulting in disordered language development. The temporal processing deficit occurs across multiple sensory modalities, and also affects rapid and sequential motor production skills. Despite relatively normal clinical neuroradiological examinations, in vivo morphological analysis, utilizing magnetic resonance imaging techniques for quantitative volumetric measurements of specific brain structures, has identified abnormalities in superior parietal, prefrontal, and temporal cortices, as well as diencephalic and caudate nuclei. Abnormalities in structures which are involved in multimodal processing and sensory motor integration is consistent with the behavioral profile of developmental dysphasia. Two alternative hypotheses regarding the neurophysiological basis of the multimodal temporal processing disorder include: dysfunction in specific cellular systems which subserve rapid, transient processing; and abnormal gating of sensory relay by intralaminar and reticular thalamic nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354968
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  • 6
    Electronic Resource
    Electronic Resource
    Intraventricular cavernous angioma. A survey (1991)
    Springer
    Acta neurochirurgica 110 (1991), S. 140-145 
    Details
    ISSN: 0942-0940
    Keywords: Cavernous haemangioma ; intraventricular tumour ; CT ; MRI ; management ; results
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Since the availability of CT diagnostis 23 cases of intraventricular cavernous angioma (IVCA) have been published in the literature. Three additional cases have been operated upon in our Department. Based on these 26 cases the clinical data, radiological findings, treatment and outcome of IVCAs are reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01400682
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  • 7
    Electronic Resource
    Electronic Resource
    MRI evaluation of the levator ani muscle: anatomic correlations and practical applications (1991)
    Springer
    Surgical and radiologic anatomy 13 (1991), S. 129-131 
    Details
    ISSN: 1279-8517
    Keywords: Levator ani muscle ; MRI ; Anorectal anomalies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé A partir de l'étude comparative de coupes anatomiques dans les plans transversal, frontal, sagittal et des coupes IRM correspondantes du petit bassin, les auteurs déterminent quels sont les plans de coupe et les modes IRM les plus performants pour l'étude morphologique des muscles élévateurs de l'anus. Cette étude montre l'intérêt de l'examen IRM dans le bilan des malformations ano-rectales opérées.
    Notes: Summary A comparative study of serial anatomic sections in the transverse, frontal and sagittal planes with corresponding MRI sections of the pelvis allowed the authors to define the most suitable sectional planes and MRI modes for a morphologic study of the levator ani muscle. This study shows the value of MRI examination in the assessment of anorectal malformations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01623886
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  • 8
    Electronic Resource
    Electronic Resource
    A new cephalic reference plane for use with magnetic resonance imaging: the chiasmato-commissural plane (1991)
    Springer
    Surgical and radiologic anatomy 13 (1991), S. 197-201 
    Details
    ISSN: 1279-8517
    Keywords: MRI ; Brain ; Reference plane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé Définition en résonance magnétique d'un plan de référence céphalique alignant le point chiasmatique et la commissure postérieure, facilement déterminé sur une coupe sagittale médiane et permettant d'orienter les coupes horizontales selon une direction proche du sillon latéral, et de façon quasiment orthogonale à l'axe du tronc cérébral.
    Notes: Summary A cephalic reference plane is described through the chiasmatic notch and the posterior commissure, which is easily identified on mid-sagittal cuts using magnetic resonance imaging. The horizontal cuts so obtained are almost parallel to the lateral fissure and are perpendicular to the axis of the brain stem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01627986
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  • 9
    Electronic Resource
    Electronic Resource
    Cystic acoustic schwannomas (1991)
    Springer
    Acta neurochirurgica 110 (1991), S. 120-123 
    Details
    ISSN: 0942-0940
    Keywords: Cerebello-pontine angle lesions ; acoustic schwannoma ; cyst ; CT ; MRI ; differential diagnosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Three cases with large space-occupying cysts in the cerebellopontine angle are reported. CT and MRI findings were not typical for acoustic schwannomas but at operation, besides the large cysts, small acoustic schwannomas could be detected and removed. The clinical and neuroradiological features of this unusual varietyand the CT and MRI differential diagnosis of cerebellopontine angle lesions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01400678
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  • 10
    Electronic Resource
    Electronic Resource
    Benign symptomatic lesions of the pineal gland. Report of seven cases treated surgically (1991)
    Springer
    Acta neurochirurgica 108 (1991), S. 40-44 
    Details
    ISSN: 0942-0940
    Keywords: Pineal cyst ; enlarged pineal gland ; infratentorial supracerebellar approach ; MRI ; occlusive hydrocephalus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Seven patients with non-neoplastic symptomatic lesions of the pineal gland have been operated on in our department since 1988. Clinical symptoms were slight and there were intermittent signs of a space occupying lesion in the quadrigeminal area, i.e. visual and gait disturbances. In three patients, obstructive hydrocephalus with related symptoms was found. Diagnosis was confirmed by use of MRI in sagittal planes, revealing a cystic lesion in five and a solid tumour in two patients. All patients were operated on without complications using an infratentorial supracerebellar approach. Histological examination showed glial cysts of the pineal gland in five patients. In the two solid specimens, normal pineal tissue was found. These lesions seem to be of special interest, as the only pathological property are their size: Both lesions — “too large pineal glands” — caused obstruction of the outlet of the third ventricle with subsequent hydrocephalus. Surgical treatment was curative in all cases with prompt relief of the symptoms. Clinical symptoms and signs, diagnostic and pathological findings, as well as the surgical results of these cases will be reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01407665
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  • 11
    Electronic Resource
    Electronic Resource
    The importance of MRI findings for the diagnosis of nontraumatic lumbar subacute subdural haematomas (1991)
    Springer
    Acta neurochirurgica 113 (1991), S. 186-188 
    Details
    ISSN: 0942-0940
    Keywords: MRI ; spinal subdural haematoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Spinal subdural haematoma (SSH) is a rare cause of spinal cord or cauda equina compression which occurs mainly in patients with a bleeding diathesis. This report presents a case of subacute lumbar subdural haematoma demonstrated by magnetic resonance imaging. MRI appears to be more sensitive than myelography and CT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403207
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  • 12
    Electronic Resource
    Electronic Resource
    Anterior-sacral meningocele; value of magnetic resonance imaging and abdominal sonography (1991)
    Springer
    Acta neurochirurgica 109 (1991), S. 154-157 
    Details
    ISSN: 0942-0940
    Keywords: Sacral meningocele ; MRI ; ultrasound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary With the presentation of a case of giant anterior sacral meningocele, the evident superiority of magnetic resonance imaging over any other methods for the diagnosis of this rare condition is demonstrated. Ultrasound as a screening tool is often the first to reveal the presence of the intrabdominal cystic abnormality and furthermore is an excellent means for checking the post-operative course. In addition this particular case is interesting because the dural stalk linking the meningocele to the dural abdominal sac was not entirely free from nervous structures inspite of macroscopic appearances to the contrary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403013
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  • 13
    Electronic Resource
    Electronic Resource
    MRI — a noninvasive tool for evaluating therapeutic embolisation of cerebral arteriovenous malformations (1991)
    Springer
    European radiology 1 (1991), S. 51-57 
    Details
    ISSN: 1432-1084
    Keywords: Arteriovenous Malformations ; Celebral ; Endovascular Therapy ; MRI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Of 86 patients with whose cerebral arteriovenous malformations (AVMs) were embolised in the period 1985–1990 29 were examined by high-field spin-echo (SE) magnetic resonance imaging (MRI) after endovascular therapy with gistoacryl-lipiodol. Embolisation-related changes in the nidus of the AVM and in the surrounding brain parenchyma were assessed. Results were compared with pretreatment MR and CT, and with follow-up angiograms in all patients. In accordance with angiographic findings, complete obliteration of pathological vessels was noted in 7 patients (24.1%) and partial occlusion in 22 (75.9%); small ischaemic infarcts were observed in 8 patients (27.6%) and extravascular deposits of blood breakdown products were seen in 3 (10.3%). MRI is a valuable noninvasive technique for assessing morphology and haemodynamics of cerebral AVMs before and after treatment. However, following embolotherapy, variable effects on signal intensity in vascular lumina caused by flowing blood, thrombosis and the embolisation agent have to be carefully analysed. To assess the exact site of histoacryl-lipiodol in embolised nidus territories or small areas of possible intracerebral hemorrhage, the time interval between endovascular therapy and MR examinations may have to be modified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540104
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  • 14
    Electronic Resource
    Electronic Resource
    MRI in spontaneous dissection of vertebral and carotid arteries (1991)
    Springer
    Neuroradiology 33 (1991), S. 111-113 
    Details
    ISSN: 1432-1920
    Keywords: Carotid artery ; Vertebral artery ; Dissection ; MRI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Fifteen patients were observed between 1987 and 1990: there were six with angiographically confirmed vertebral artery dissection, and 9 with carotid artery dissection. Results showed concordance of MRI and angiographic findings, in all cases but one. The dissected portion consistently showed a semilunar hyperintensity narrowing the residual eccentric signal void of the lumen when the artery was not completely occluded. In one angiographically occluded vessel, MR detected a small signal void within the hyperintensity, indicating that the artery was not completely occluded. The length of the dissected portion was clearly demonstrated by MR. Follow up MR and angiographic studies confirmed the regression of the dissection, and also allowed examination of the cerebral parenchyma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588245
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  • 15
    Electronic Resource
    Electronic Resource
    Resolving MRI abnormalities with progression of subacute sclerosing panencephalitis (1991)
    Springer
    Neuroradiology 33 (1991), S. 178-180 
    Details
    ISSN: 1432-1920
    Keywords: Subacute sclerosing panencephalitis ; MRI ; Relapsing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Serial MRI was performed on a 15 year old girl with Subacute Sclerosing Pan-encephalitis (SSPE). After a period of remission she entered a phase of progressive deterioration. A repeat MRI showed significant resolution of the previous abnormalities. Her pathology and MRI scans are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588264
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  • 16
    Electronic Resource
    Electronic Resource
    Primitive neuroectodermal tumor of the leptomeninges (1991)
    Springer
    Neuroradiology 33 (1991), S. 260-263 
    Details
    ISSN: 1432-1920
    Keywords: Primitive neuroectodermal tumor ; Leptomeninx ; CT ; MRI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Primitive neuroectodermal tumor (PNET) without an obvious intraparenchymal mass lesion and with diffuse spread in the subarachnoid space is rare. We report such a rare case and discuss the computed tomography (CT) and magnetic resonance (MR) features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588232
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  • 17
    Electronic Resource
    Electronic Resource
    MRI of subarachnoid dissemination of medulloblastoma (1991)
    Springer
    Neuroradiology 33 (1991), S. 264-268 
    Details
    ISSN: 1432-1920
    Keywords: MRI ; Gadolinium-DTPA ; Medulloblastoma ; Subarachnoid dissemination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We report two cases with subarachnoid dissemination of medulloblastoma depicted clearly by Gadolinium-DTPA enhanced MRI. We also demonstrate the superiority of Gadolinium-DTPA enhanced MRI over nonenhanced MRI, CT, myelography and postmyelographic CT for diagnosing subarachnoid dissemination and for monitoring the response to therapy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588233
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  • 18
    Electronic Resource
    Electronic Resource
    Radiation myelopathy: significance of gadolinium-DTPA enhancement in the diagnosis (1991)
    Springer
    Neuroradiology 33 (1991), S. 286-289 
    Details
    ISSN: 1432-1920
    Keywords: Radiation myelopathy ; MRI ; Gadolinium ; DTPA enhancement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We described two cases of chronic progressive radiation myelopathy (CPRM), in which magnetic resonance imaging (MRI) was of great value for the diagnosis. Gadolinium-DTPA (Gd-DTPA) enhancement delineated precise lesions responsible for Brown-Séquard syndrome caused by CPRM in both cases. This safe, sensitive procedure will be a requisite study in patients who are suspected of CPRM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588240
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  • 19
    Electronic Resource
    Electronic Resource
    MRI demonstration of uncal herniation caused by arachnoid cyst in the Sylvian fissure (1991)
    Springer
    Neuroradiology 33 (1991), S. 346-348 
    Details
    ISSN: 1432-1920
    Keywords: MRI ; Uncal herniation ; Arachnoid cyst ; CT
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We report a case of arachnoid cyst in the Sylvian fissure which progressed to uncal herniation. MRI was shown to be superior in visualizing uncal herniation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587821
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  • 20
    Electronic Resource
    Electronic Resource
    MRI diagnosis of thoracic ossification of posterior longitudinal ligament with concomitant disc herniation (1991)
    Springer
    Neuroradiology 33 (1991), S. 455-457 
    Details
    ISSN: 1432-1920
    Keywords: MRI ; Myelopathy ; Posterior longitudinal ligament
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Ossification of the posterior longitudinal ligament is a potentially curable cause of thoracic myelopathy. As this case illustrates, MRI can confirm the diagnosis, demonstrate other concomitant pathology such as disc herniation, and help assess the clinical significance of OPLL by showing spinal word compression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00598627
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  • 21
    Electronic Resource
    Electronic Resource
    MRI with Gd-DTPA in tumours of larynx and hypopharynx (1991)
    Springer
    European radiology 1 (1991), S. 58-64 
    Details
    ISSN: 1432-1084
    Keywords: MRI ; Larynx ; Hypopharyngeal tumours ; Contrast media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Twenty-eight patients with tumours of the larynx, divided into supraglottic, glottic, and subglottic lesions, and of the hypopharynx were examined by different MRI techniques using the paramagnetic contrast medium Gd-DTPA. The results of preoperative MRI were compared with clinical laryngoscopy and the pathological tumour classification. The examinations were carried out using plain T1-wand T2-weighted and Gd-DTPA enhanced T1-weighted sequences. Most studies included three slice orientations for optimal assessment of different tumour locations. The most accurate diagnostic information was given by Gd-DTPA-enhanced sequences. The combination of plain images, contrast-enhanced images and subtraction enabled precise assessment of deep infiltration. T2-weighted and proton density sequences conveyed more information about cartilage invasion and liquid-filled structures, but gave more artefacts than T1-weighted images. Laryngoscopy had advantages in T1-classified tumors, as the extent of the tumor could be seen, and offered histological information via biopsy. Diagnostic findings of MRI correlated in 85.7% with the pathologist's report, and laryngoscopy provided exact classification in only 64.3% of patients. Gd-DTPA-enhanced MRI is an important adjunct to non-contrast MR studies, and forms an ideal diagnostic supplement to laryngoscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540106
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  • 22
    Electronic Resource
    Electronic Resource
    Brainstem compression by basilar artery anomalies as visualized by MRI (1991)
    Springer
    Journal of neurology 238 (1991), S. 49-50 
    Details
    ISSN: 1432-1459
    Keywords: Basilar artery ; Aneurysm ; MRI ; Brainstem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The use of MRI in the diagnosis of vascular anomalies of the basilar artery is demonstrated in two cases. The first patient had a partially thrombosed giant aneurysm of the basilar artery; the second had an atypical course of the basilar artery. MRI is indicated whenever other imaging procedures do not provide a definite diagnosis or the use of contrast medium for conventional X-ray examination or computed tomography is contraindicated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319712
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  • 23
    Electronic Resource
    Electronic Resource
    Cerebral cavernous malformations (cavernomas) in the pediatric age-group (1991)
    Springer
    Child's nervous system 7 (1991), S. 139-146 
    Details
    ISSN: 1433-0350
    Keywords: Vascular cerebral malformations ; Cavernous angiomas ; Epilepsy ; Childhood ; CT ; MRI ; Cavernoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cavernomas are vascular malformations composed of a compact mass of sinusoidal-type vessels that are immediately contiguous with one another and have no intervening parenchyma. Cavernous malformations were previously held to be a rare pathology occurring predominantly in adults. New neuroradiological techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) demonstrate, on the contrary, that these lesions are also more frequent during childhood than was previously thought. In our institution we observed 17 cases of cavernous malformations in patients aged between 18 months and 16 years, 16 of whom were diagnosed after 1982. In 4 of these cases there was a documented familial history; in 2 multiple malformations were present. The most common site was the subcortical frontal region, but in 1 case the malformation was located in the pineal region. The most frequent (in 12 cases) initial symptom was hemorrhage, with the characteristics of an intracerebral hematoma. In 4 cases the initial symptom consisted of epileptic fits and 2 of these patients subsequently suffered hemorrhage. In one case the symptoms observed were those of an expansile process. All our patients underwent cerebral angiography and only in 1 case did this show a vascular abnormality. CT, performed in 16 patients, gave positive results in all cases. MRI, performed in 12 patients, gave highly significant images in all cases. Radical surgical removal of the malformation was performed in 15 of the 17 patients, and the results can be considered excellent in the majority of cases. Cavernous malformations are, therefore, more frequent lesions than had previously been thought, especially in pediatric patients. MRI offers the most conclusive means of diagnosis and, considering the possibility of family predispositions, this is also the method to be used in screening a patient's family members. The operation is easy, at least for the most frequent location, and is justified in view of the risk of hemorrhage and relapses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00776709
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  • 24
    Electronic Resource
    Electronic Resource
    Die validität der Kernspintomographie bei der Beurteilung der traumatisierten Bandscheibe (1991)
    Springer
    Langenbeck's archives of surgery 376 (1991), S. 346-350 
    Details
    ISSN: 1435-2451
    Keywords: Spine fracture ; MRI ; Validity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die Validität der Kernspintomographie bei der Beurteilung der traumatisierten Bandscheibe wurde im Rahmen einer prospektiven diagnostischen Studie im Vergleich zur intraoperativen Diskographie als Goldstandard ermittelt. Die Untersuchungen wurden an beiden dem Frakturwirbel benachbarten Bandscheiben von 27 Patienten, deren Wirbelfraktur operativ behandelt worden war, durchgeführt. Die Sensitivität der Kernspintomographie als nichtinvasives Untersuchungsverfahren betrug 96%, die Spezifität 75%. Diese Werte entsprechen einer Validität von 88%.
    Notes: Summary The validity of the magnetic resonance imaging (MRI) in the diagnosis of injured intervertebral discs was examined by a prospective diagnostic study. The golden standard being intraoperative discography. The examinations were carried out on both intervertebral discs adjoining the fractured vertebral body. There were 27 patients with 54 injured discs. The sensitivity of the MRI as a noninvasive method is 96%, the specifity is 75%. These results comply with a validity of 88%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00186427
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    Electronic Resource
    Electronic Resource
    EEG laterality in the era of structural brain imaging (1991)
    Springer
    Brain topography 3 (1991), S. 381-390 
    Details
    ISSN: 1573-6792
    Keywords: EEG laterality ; MRI ; The 10–20 system ; Alpha rhythm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Bilateral EEG recording is a common practice when brain laterality needs to be assessed in cognitive neurophysiology and psychiatry research. Its precision and validity remain uncertain. With structural brain imaging methods, it is possible to examine EEG electrode placements according to the 10–20 system and the validity of inferences made on derived data. Frequent sources of placement errors are examined along with important factors that contribute to EEG imbalance. Examples are mentioned where asymmetries of EEG/ERP caused by cranial and parenchymal brain asymmetries may be mistaken for cognition-related laterality changes. Because external skull landmarks are not reliable predictors of cranial and parenchymal brain asymmetries, laterality assessment cannot be guaranteed by the 10–20 system. Consequently, a return, on a case-to-case basis, to nonstandard montages, assisted by structural brain imaging is seen as an acceptable alternative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01129641
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    Electronic Resource
    Electronic Resource
    Accurate Matching of electromagnetic dipole data with CT and MR images (1991)
    Springer
    Brain topography 3 (1991), S. 425-432 
    Details
    ISSN: 1573-6792
    Keywords: CT ; Dipole ; EEG ; Epilepsy ; Multimodality Matching ; MEG ; MRI ; Volume Visualization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Interpretation of EEG (electroencephalography) or MEG (magnetoencephalography) derived three-dimensional dipole localizations is hampered by poor visualization. This paper describes a method for combining dipole data with structural image data of the same patient. To ensure high precision this method utilizes external markers that are easy to apply. These markers can achieve subslice accuracy and can even be used to pinpoint reference points outside the scanned volume. Accurate matching is thus provided even in standard imaging protocols employing thick slices and/or large interslice gaps. The results of the matching method are presented in 2D and 3D visualizations. The hybrid images facilitate the interpretation of dipole localizations with respect to the patient's anatomy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01129001
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  • 27
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    Seeing through the skull: Advanced EEGs use MRIs to accurately measure cortical activity from the scalp (1991)
    Springer
    Brain topography 4 (1991), S. 125-131 
    Details
    ISSN: 1573-6792
    Keywords: High-resolution EEG ; Evoked potential ; MRI ; Spatial signal enhancement ; Deblurring ; Finite element model ; Laplacian derivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary There is a vast amount of untapped spatial information in scalp- recorded EEGs. Measuring this information requires use of many electrodes and application of spatial signal enhancing procedures to reduce blur distortion due to transmission through the skull and other tissues. Recordings with 124 electrodes are now routinely made, and spatial signal enhancing techniques have been developed. The most advanced of these techniques uses information from a subject's MRI to correct blur distortion, in effect providing a measure of the actual cortical potential distribution. Examples of these procedures are presented, including a validation from subdural recordings in an epileptic patient. Examples of equivalent dipole modeling of the somatosensory evoked potential are also presented in which two adjacent fingers are clearly separated. These results demonstrate that EEGs can provide images of superficial cortical electrical activity with spatial detail approaching that of O15 PET scans. Additionally, equivalent dipole modeling with EEGs appears to have the same degree of spatial resolution as that reported for MEGs. Considering that EEG technology costs ten to fifty times less than other brain imaging modalities, that it is completely harmless, and that recordings can be made in naturalistic settings for extended periods of time, a greater investment in advancing EEG technology seems very desirable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01132769
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    Leukoaraiosis: A reappraisal. II. MRI studies (1991)
    Springer
    Neurological sciences 12 (1991), S. 269-279 
    Details
    ISSN: 1590-3478
    Keywords: Cerebrovascular disease ; cerebral arteriosclerosis ; leuko-encephalopathy ; aging ; MRI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Sommario La Risonanza Magnetica è più sensibile della TC nei confronti delle alterazioni della sostanza bianca encefalica di incerto significato osservate in soggetti anziani denominate leucoaraiosi. Studi clinici trasversali hanno dimostrato che la presenza o l'estensione di queste alterazioni è maggiore in soggetti con malattia cerebrovascolare o fattori di rischio vascolari. Studi patologici hanno rivelato che alterazioni di diverso tipo possono essere sottese alle lesioni focali: infarti lacunari completi ed incompleti, stato cribroso, spaziperivascolari (di Virchow-Robin) dilatati, demielinizzazione e gliosi. Più difficoltosa è attualmente l'interpretazione del significato delle lesioni diffuse. Queste potrebbero corrispondere ad uno stadio evolutivo delle lesioni focali, oppure essere il risultato di una ischemia diffusa della sostanza bianca. In alternativa potrebbero essere correlate ad alterazioni del flusso liquorale trans-ependimale. Studi longitudinali in soggetti asintomatici con correlazione dei reperti della Risonanza Magnetica con dati clinici, fisiopatologici ed istopatologici, sono necessari per una migliore comprensione del significato e del valore prognostico delle alterazioni della sostanza bianca corrispondenti alla leuco-araiosi. È questo presupposto indispensabile per la definizione di strategie terapeutiche mirate a prevenire o curare tali alterazioni.
    Notes: Abstract Magnetic resonance imaging is more sensitive than computed tomography to brain white matter changes of undefined significance observed in elderly subjects termed leuko-araiosis. Cross-sectional clinical studies have shown that these changes are more frequent or are more extensive in patients with cerebrovascular disease or vascular risk factors. Pathological studies have revealed that a number of alterations may underlie focal white matter changes including complete and incomplete lacunar infarcts, état criblé, dilated perivascular (Virchow-Robin) spaces, demyelination, and gliosis. Diffuse white matter changes are more difficult to explain. These might result from confluence of focal changes, or from diffuse white matter ischemia (incomplete infarct). Alternatively, they may be related to alterations of the transependymal CSF flow. Longitudinal studies in asymptomatic subjects correlating the MRI picture with clinical, pathophysiological, and histopathological data are needed in order to establish the significance and prognostic value of the different processes underlying LA, and to plan therapeutic strategies to prevent or treat them.
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    URL: http://dx.doi.org/10.1007/BF02337774
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    Neuroradiological, neurophysiological and anatomopathological study of a case of locked-in syndrome (1991)
    Springer
    Neurological sciences 12 (1991), S. 317-321 
    Details
    ISSN: 1590-3478
    Keywords: Locked-in syndrome ; CT ; MRI ; BAEPs ; SEPs ; TEPs ; MAPs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Sommario Viene riportato un caso anatomoclinico di “Locked in” syndrome e riferiti i risultati delle indagini Neuroradiologiche e Neurofisiologiche. In particolare la RMN conferma la sua utilità diagnostica nella patologia della fossa cranica posteriore; lo studio neurofisiologico (BAEPs, SEPs, MAPs, TEPs) evidenzia che la lesione, sul piano funzionale, può in realtà essere più estesa di quanto dimostrato dagli esami neuroradiologici e dai dati anatomopatologici. I potenziali evocati possono quindi assumere una considerevole importanza per una precisa localizzazione delle lesioni troncali.
    Notes: Abstract We report an anatomoclinical case of locked-in syndrome together with the neuroradiological and neurophysiological findings. MRI confirmed its value in the diagnosis of posterior cranial fossa pathology while the neurophysiological work-up (BAEPs, SEPs, MAPs and TEPs) revealed that the lesion may have broader functional implications than may be gauged from the neuroradiological and pathological evidence. Evoked potentials may therefore be of considerable importance in pinpointing brainstem lesions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02337780
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    Comparative evaluation of SPECT, CT and CW Doppler data in patients with ischemic lesions of the brain (1991)
    Springer
    Neurological sciences 12 (1991), S. 377-382 
    Details
    ISSN: 1590-3478
    Keywords: Ischemic cerebrovascular lesions ; 99mTc-HMPAO-SPECT ; CT ; CW Doppler US ; digital subtraction angiography ; carotidography ; MRI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Sommario Gli autori presentano i dati SPECT, TC, e CW DOPPLER in una casistica di 117 pazienti affetti da lesioni ischemiche cerebrali e correlano i risultati di tali indagini con il quadro clinico. Evidenziano inoltre la sensibilità dell'esame SPECT-PAO per la localizzazione di lesioni focali nei confronti della TC che nel 50% dei casi risulta normale o evidenzia un quadro di atrofia cerebrale. In questi sessi casi l'esame CW Doppler, eseguito a livello dei tronchi sopraortici, dimostra alterazioni cricoscritte o diffuse. Sulla base dei dati forniti dalla CW Doppler e dalla SPET gli autori ritengono pertanto che il reperto TC di atrofia cerebrale possa essere espressione di una alterazione della perfusione e del metabolismo cerebrale quindi debba essere rivalutato per la diagnosi e la prognosi di pazienti affetti da lesioni ischemiche cerebrale li.
    Notes: Abstract We report the SPECT, CT and CW Doppler findings in a series of 117 patients with cerebral ischemic lesions and correlate them with the clinical finding SPECT-PAO proved to be more sensitive in localizing focal lesions than CT which in 50% of the cases was normal or yielded an image of cerebral atrophy. In the latter cases CW Doppler ultrasound on the supraaortic trunks showed changes, circumscribed or diffuse. On the CW Doppler and SPECT evidence we consier that the CT image of cerebral atrophy may denote an alteration of the cerebral blood flow and metabolism and should be assessed in this light in the diagnosis and prognosis of cerebral ischemic lesions.
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    URL: http://dx.doi.org/10.1007/BF02335777
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  • 31
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    Origin of apparent swain-schaad deviations in criteria for tunneling (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 361-366 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational analysis calculations have been conducted in an effort to understand the origins of apparently anomalous relationships reported between kH/kT and kD/kT kinetic isotope effects. The actual isotopic substitutions used in previous work are more complex than a simple comparison between H/T and D/T isotope effects. The relationships between the actual isotope effects determined in these studies amount to tests of two standards of conventional isotope effect theory, the rule of the geometric mean (or the lack of isotope effects on isotope effects) and the Swain - Schaad rule. Model calculations illustrate the importance of violations of the rule of the geometric mean (over Swain - Schaad deviations) arising in models that incorporate both explicit reaction-coordinate coupling of two isotopic sites and reaction-coordinate tunneling. Implications for experimental studies of turneling using apparent Swain - Schaad exponents are discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040607
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    The schiff base between pyridoxal-5′-phosphate (PLP) and hexylamine. Formation of the unprotonated form of the imine by reaction of the unprotonated PLP and free amine (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 372-380 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electrochemical and spectrophotometric studies of the pyridoxal-5′ -phosphate hexylamine Schiff base (PHSB) in strongly basic media were carried out. The equilibrium constant and rate constants of the formation and hydrolysis of the unprotonated imine from the unprotonated pyridoxal-5′ -phosphate and free amine were determined by linearscan cyclic voltammetry. The acid-base dissociation constant of the imine group was obtained by spectrophotometric measurements. Absorption bands for the free imine and the conjugate acid are characterized by a log-normal distribution. These studies are for general application to the quantitative characterization of non-enzymatic model compounds.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040609
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    Factors affecting the reversibility of the electrophilic step in olefin bromination. The case of 5H-dibenzo [a, d] cycloheptene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 387-398 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The tendency of ion-pair intermediates generated by treatment of trans-10-bromo-10, 11-dihydro-11-hydroxy-5H-dibenzo [a, d] cycloheptene (5) with HBr to release Br2 giving 5H-dibenzo [a, d,] cycloheptene (1) has been evaluated. The observed 9:1 ratio between ion-pair collapse to the trans-dibromide (7) and Br2 release to olefin 1, as compared with the 3:7 ratio found with the 5H-dibenz [b, f] azepine-5-carbonyl chloride system, has been interpreted as indicating a much lower propensity for reversibility of ion-pair formation in the bromination of 1. The structural parameters obtained by x-ray diffraction of the dibromide 7 show for this compound an angle strain at C-10 and C-11 analogous to that found in trans-10, 11-dibromo-10, 11-dihydro-5H-dibenz [b, f,] azepine-5-carbonyl chloride. Olefin 1 adds Br2 in 1,2-dichloroethane at 25°C according to a third-order rate law, with k3 = 30(3) M-2 s-1. About 10% of 5-bromo-5H,-dibenzo [a, d] cycloheptene, arising from collapse of a dibenzo [a, d] tropylium ion intermediate (9), is formed in this reaction besides the expected trans-dibromide 7. Spectral evidence for the formation of 9, arising by rearrangement of a first formed weakly bridged ionic intermediate in the reaction of 1 with Br2, is presented. the results obtained with the 5H-dibenzo [a, d,] cycloheptene system have been rationalized on the basis of the formation of very weakly bridged intermediates having a much lower tendency to revert back to olefin and Br2 with respect to the corresponding symmetrically bridged bromonium ions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040611
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    SRN1 Reactions of nucleophiles with radical clocks: Rate constants for some radical-nucleophile reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 404-412 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Treatment of o-3-(but-3-enyloxy)benzene (1) with anions -SPh, -PPh2 and -PO(OEt)2 in ammonia, acetonitrile or dimethyl sulphoxide gives both direct substitution and cyclized products. The formation of the latter confirms the intermediacy of the o-3-(but-3-enyloxy)phenyl radical (2) and confirms that the reactions follow the SRN1 pathway. The kinetics of the coupling of the aryl radical 2 were determined by comparison with the known rate of cyclization of 2. Similar experiments with the neopentyl bromide, 6-bromo-5,5-dimethylhex-1-ene, and its 3-oxa derivative also gave cyclized and uncyclized products, thus confirming that the SRN1 mechanism applies to the reactions. Approximate rate constants for the coupling of a neopentyl radical with the nucleophiles -SPh and -PPh2 have thus been determined.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040703
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    Short Communications. Biphenyl-3,4′-Dinitrene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 459-462 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of biphenyl-3,4′ -diazide in a rigid glassy matrix at 77 K yields quintet state biphenyl-3,4′ -dinitrene with zero-field splitting parameters of |D/hc- = 0.153 cm-1 and |E/hc| = 0.019 cm-1 determined by electron spin resonance spectroscopic studies. Curie plot studies are consistent with assigning the quintet to be the ground state in this species. This finding confirms qualitative connectivity-based predictions for this general connectivity type of openshell system, and is in qualitative agreement with spectral INDO-CI computational predictions for both planar and twisted geometries of the dinitrene.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040708
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    The α-bromocyclohexanone ring: The relationship between its conformation and the ultraviolet and infrared absorption of the keto group (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 420-438 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of diterpenoids whose C-ring was an α-bromocyclohexanone showed a discontinuity in the relationship between the Br—C—C=O torsion angle and the Br…O contact distance at about 50°, below which the Br…O distance remained effectively constant at about 3.0 Å. This effect is caused by the non-compressibility of the van der Waals radii of the Br and O atoms. Analysis of the parameters for all compounds in the Cambridge Data File containing an α-bromocyclohexanone ring confirmed this phenomenon. Once the Br…O distance approaches 3.0 Å, the Br—C—C and C—C=O angles are forced open to accommodate the Br…O compression strain as the torsion angle is further reduced. An approximate value of the Br…O distance, d in Å, can be estimated for any torsion angle, ø, by the empirical equation d2 = R - S cos φ + T cos2 φ where R = 11.73, S = 3.62 and T = 0.75. There is a linear relationship between the Br…O separation and both the infrared vibration frequency v and the ultraviolet absorption wavelength δmax of the C=O group: the greater the distance, the lower is the frequency v and longer the wavelength δmax. Thus measurement of the ultraviolet and infrared spectra of a compound containing an α-bromocyclohexanone system can yield information about the Br…O distance and hence the conformation of the six-membered ring. There are also systematic trends in the effect on the spectroscopic properties of the keto group that accompany changing the halogen from fluorine through to iodine. When the halogen is axial, its electronegativity has a maximum influence on the C=O vibration frequency by a ‘through-bond’ inductive process. When the halogen is equatorial, it exerts a steric compression on the non-bonded electrons in the 2p orbital of the oxygen atom. This enhances hybridization to the sp2 state and this simultaneously strengthens the C=O bond and enlarges the n → π* energy gap. This ‘through-space’ influence is simply a process of steric compression, dependent on the size of the halogen atom. It accounts well for all of the systematic trends in both infrared and ultraviolet frequencies of the C=O group when the halogen is equatorial and eclipses the C=O bond.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040705
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040801
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  • 38
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    Treatment of electrostatic effects within the molecular mechanics method. 3. Double bonds and conjugated systems (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 467-478 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The previously developed general method (IDME), which includes calculation of electrostatic and solvation effects on conformational equilibria, has been extended to molecules containing double bonds and conjugated systems. It was applied in connection with MM2 studies to the calculation of the charge distributions and dipole moments, and to the conformational energies of some β-substituted cyclohexenes, exo-methylenecyclohexanes and benzocycloheptenes. Conformational equilibria and dipole moments were well calculated. It was concluded that electrostatic interactions do not play a major role in determining conformational preferences in these compounds. On the other hand, the energies of the preferred conformations of the ten-membered ring in (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one are poorly calculated without the IDME procedure, and fairly well with it.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040802
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    Theoretical models for the reduction of arylmethyl halides by triorganotin hydridesPreliminary presentation of results at combined 45th Northwest-10th Rocky Mountain Regional Meeting of the American Chemical Society, Salt Lake City, UT, 13 June 1990. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 485-491 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two mechanistic pathways have been proposed for halogen atom transfer from the benzylic positions of halomethylarenes to triorganotin radicals. These are direct atom abstraction, which might involve an extremely polar transition state, and single electron transfer followed by bond cleavage. AM1 semi-empirical calculations have been utilized to model the rate-determining step of these processes. A wide range of related families of compounds have been studied, including substituted halomethylbenzes, selected halomethyl-substituted polycyclic aromatic hydrocarbons and oxygen- and nitrogen-containing chloromethyl-substituted heteroaromatic systems. Although these calculations are relatively simple, the present results corroborate the view that chlorine and bromine atom transfer from the benzylic position to triorganotin radicals involves a direct atom abstraction in the rate-determining step whereas reduction of the corresponding iodides proceeds via an electron-transfer mechanism.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040804
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  • 40
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    Ambident electrophilicity of alkyl aryl phosphates (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 516-522 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrolysis of dimethyl aryl phosphates, (MeO)2P(O)OAr where the ArO group is derived from N-methyl-8-hydroxyquinolinium or 4-hydroxy-(N,N,N-trimethylanilinium) ion, proceeds with the cleavage of the P—OAr and Me—O bonds. The effect of external factors on the relative contributions of those two reaction pathways was studied. The increase in temperature favours, owing to the difference in activation entropies, the reaction at carbon. The addition acetone to the aqueous reaction medium slows down the reaction at carbon more rapidly than the reaction at phosphorus, indicating higher hydration requirements of the dealkylation transition state. In water-triffuoracetic acid mixtures only the P—OAr bond cleavage is acid catalysed; the catalytic effect is superimposed on the general, decelerating medium effect. Specific nucleophilic catalysis was demonstrated for the Me—O bond fission by thiosulphate ion (ca 60-fold acceleration), and for the reaction at phosphorus by fluoride ion (ca 500-fold acceleration).
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040807
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040901
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  • 42
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    Short communication. Structural studies of bromine adducts of 1,2- and 1,4-bis(phenylseleno)benzenes. Evidence for the (TB, MC) structure of 1,2-(PhSeBr2)2C6H4 (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 523-525 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1,2-Bis(phenylseleno)benzene reacted with equimolar amount of bromine to yield a trigonal bipyramidal (TB) adduct, in contrast to the molecular complex (MC) structure of selenanthrene with bromine. Whereas the structure of 1,4-(PhSeBr2)2C6H4 was (TB, TB) at the two selenium atoms, that of the 1,2-derivative was demonstrated to be (TB, MC), the first example of an MC structure of PhSeC6H4Y with Br2 [Y = 2-PhBr2Se(TB)]. Both electronic and steric effects of the group must play an important role in MC formation. Rapid structural exchange in this tetrabromide, (TB, MC) ⇄ (MC, TB), was also observed.
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    Conformations of pentan-1-OL, hexan-1-OL and their thio analogues (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 536-540 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Empirical linear relationships between standard Gibbs free energy, ΔG298°, and parachor and between standard entropy, S298°, and parachor are presented for the aliphatic series H(CH2)nX with X = CH3, CH=CH2, C≡CH, Cl, OH, SH, SCH3 and SC2H5. In the series with X = OH and SH significant deviations of points for n = 4 and 5 are observed. INDO quantum-chemical analysis points to the formation of cyclic conformers of butan-1-ol, pentan-1-ol and their corresponding thio analogues. The formation energy of the cyclic conformers (higher for thiols than for alcohols) is proportional to the sum of deviations from the linearity of the points under discussion.
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  • 44
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    Review commentary. Solvation, the electrophilic driving force of ionic bromination of ethylenic compounds. The addition-solvolysis analogy (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 527-535 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvation is the main driving force of electrophilic bromination since it is impossible to obtain a bromonium ion from bromine and alkene in the gas phase, whereas it is a very fast reaction in solution. The role of a protic solvent in this addition was investigated experimentally by extended Winstein-Grunwald relationships, kinetic solvent isotope effects and R, the rate ratios in two solvents of similar ionizing powers but different nucleophilicities. It is shown that electrostatic medium effects and electrophilic assistance to bromide ion departure are the main rate-determining factors of the reaction. These two contributions are roughly independent of the double bond substituents. Nucleophilic solvent assistance to positive charge development is also found; however, it provides only a small acceleration, the magnitude of which depends on alkene structure. This nucleophilic solvent involvement is annulled when crowded substituents inhibit approach of the solvent to the cationic part of the transition state or when positive charge is delocalized by conjugated electron-donating groups. These several solvent roles are identical in nature and in magnitude with those observed in heterolytic solvolysis. In halogenated solvents, the driving force of bromination arises from catalysis by a second bromine molecule which assists heterolysis of the bromine-bromine bond, leading to the bromonium-tribromide ion pair. Similar halogen catalysis occurs also in some solvolyses. Finally, return is also found in both reactions; reversible formation of bromonium ions is observed when their nucleophilic attack, the productforming last step, is made energetically difficult either by steric inhibition or by poor nucleophilicity of the trapping nucleophiles. Similarities and differences between electrophilic bromine addition and limiting solvolysis are discussed in terms of respective intermediate stabilities and heats of formation.
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  • 45
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    Photochemical transformations. 49.For Part 48, see Ref. 1. Solvent effects on singlet ionic and triplet photoreactions of some bridged polycyclic chlorides: Comparison with ground-state reactionsDedicated to Professor Kurt Schaffner on his 60th birthday. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 541-546 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct irradiations of 2-chloro-6,7 : 8,9-dibenzotricyclo [3.2.2.02,4] nona-6,8-diene (5-Cl) were conducted in cyclohexane, acetic acid and wet acetonitrile. The products are 1-methylfluoranthene (8) in all three solvents, the allylic chlorides 8-chloro-7-methylene-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5-diene (3-Cl) and 7-chloromethyl-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5,7-triene (2-Cl) in acetic acid and acetonitrile and solvolysis product amides in wet acetonitrile. Compound 5-Cl had previously been shown to be the product of triplet sensitization of 2-Cl and 3-Cl, so that the singlet reaction reverses that of the triplet. The formation of 8 from 5-Cl was quenched with piperylene, whereas that of the allylic chlorides was not. Quantum yields of products and singlet lifetimes in the three solvents were measured. The solvent effects are discussed. Deuterium-labeling results on the formation of 5-Cl from 2-Cl and of 8 from 5-Cl are reported.
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  • 46
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    Steric effects of alkyl groups: A ‘cone angle’ approach (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 611-617 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A ‘cone angle’, θR, is defined for an alkyl group (R), which is proposed as a measure of the steric effect exerted by the group. The θR values for some 57 groups have been calculated mathematically by constructing the corresponding Corey - Pauling - Koltun molecular models. The variation in θR with the bulk of a group is satisfactory. However not all types of alkyl groups can be accommodated in this cone angle approach. In the case of the groups for which the cone angle can be measured, correspondences between θR and the two existing steric parameters (Taft's Es scale and Dubois' E′s scale) have been established. For some 23 alkyl groups θR has been used to explain the variation in the rate constant of the base-catalysed hydrolysis of RCOOEt with the nature of R. Our studies independently substantiate the basic assumptions of the Taft - Ingold hypothesis that, while the base-catalysed ester hydrolysis is mostly controlled by the steric and electronic effects of the R group, the acid-catalysed one is controlled almost solely be the steric effect.
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  • 47
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    Effect of hexadecyltrimethylammonium bromide micelles on the hydrolysis of substituted benzoate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 13-18 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alkaline hydrolysis of nine para-substituted phenyl esters of para-substituted benzoates was studied in the presence and absence of hexadecyltrimethylammonium bromide (CTAB) micelles. The second-order rate constant for alkaline hydrolysis in CTAB micelles (K2m) was calculated using a pseudo-phase ion-exchange model. the substituent effect on the second-order rate constant in the aqueous phase (k2w) and on k2m was analysed using Hammett's σ ρ plots. The calculated ρ values in micelles were 0.8 unit. larger than those in water. The effective low dielectric constant in the micellar surface may be responsible for the general effect of increasing the sensitivity of reactions to the electronic effect of substituents in micelles.
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  • 48
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    1,5-Sigmatropic shifts of bromine over a cyclopentadiene ring (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 31-47 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The intrinsic mechanism of circumambulatory rearrangements of 5-bromo-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene, 5-bromo-1,2,3,4 5-pentamethoxycarbonylcyclopentadien and 5-bromo- 1,2,3,4,5-pentaphenylcyclopentadiene due to sigmatropic shifts of bromine over the cyclopentadiene ring was proved, using the dynamic 13C and 1H NMR technique, to be governed by successive intramolecular 1,5-sigmatropic shifts. Semi-empirical AM1 and MINDO/3 calculations of reactions paths performed for fluoro-, chloro- and bromocyclopentadienes are in accord with the conclusion of a preference for a 1,5- over a 1,3-shift reaction path of halogen migration over a cyclopentadiene system. Intramolecular 1,5-sigmatropic shifts of chlorine in 5-chloro-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene with the free energy barrier of ΔG298+ = 26.1 kcal mol-1 were studied using 1H NMR spectroscopy.
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  • 49
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610040201
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  • 50
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    Specific micellar rate effects on unimolecular decarboxylation and cyclization (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 71-76 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion and cyclization of o-3-halopropyloxyloxyphenoxide ion (PhY7) (Y = Br, I) are accelerated by aqueous cationic and zwitterionic micelles. For cationic micelles the rate enhancements (kM′kW′) increase with increasing bulk of the surfactant head groups but are largest for decarboxylation. There are good linear free energy relationships between micellar effects on these reactions and the plots of log kM′ for cyclization against log kM′ for decarboxylation have slopes of 0.46 and 0.64 for Y = Br and I, respectively. Surfactants that have twin tail or tri-N-alkylbenzyloxy head groups do not fit the relationship. Despite mechanistic differences between decarboxylation and cyclization (an intramolecular SN2 reaction), similar factors control micellar effects on these reactions. In the absence of surfactant there is only a qualitative relationship between free energies of activation of cyclization and decarboxylation in different solvents.
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    Aromaticity as a multi-dimensional phenomenon (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 163-169 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The classification of aromaticity criteria is studied. New aromaticity criteria are developed and discussed. A statistical analysis of such criteria is presented and compared with a similar analysis of the recent literature. It is shown that aromaticity is at least a two-dimensional phenomenon. The classification of the compounds depends on the type of criteria included in the analysis.
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    AB initio MO study of the halogen cation basicities of some organic bases (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 177-191 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hartree - Fock calculations were performed to investigate the structure and relative stabilities of complexes between halogen cations and first- and second-row bases. It is shown by means of both a qualitative perturbation molecular orbital treatment and a topological analysis of the electronic charge density that second-row bases present enhanced halogen cation basicities compared with first-row bases. In this respect the results predict that although the fluorine cation basicity of water is smaller than its proton affinity, the fluorine cation basicities of SH2, thioether, phosphine and trimethylphosphine are considerably higher than their proton basicities. Similarly, phosphine and trimethylphosphine should have chlorine cation basicities greater than their proton affinities, in contrast with ammonia and trimethylamine. The results also show that fluorine and chlorine cation basicities are more sensitive to methyl substitution than proton affinities.
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    Micellar effects on the alkaline hydrolysis of N-alkyl-4-cyanopyridinium ions. An example of micelle-induced regiochemical selectivity (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 207-216 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of the reaction of N-alkyl-4-cyanopyridinium (RCP) ions [alkyl = CH3 (MCP), n-C4H9 (BCP), n-C8H17 (OCP), n-C12H25 (DCP)] with OH- ion in water are independent of chain length and RCP concentration up to 0.001 M. The ratios of the concentrations of the reaction products, N-alkyl-4-pyridone (P) and N-alkyl-4-carboxamidopyridinium (A), P/A, are similar for all substrates. In water the P/A ratios increase with pH, reaching a plateau value of ca 2 at pH ≥ 13. Added salts slightly decrease the reaction rate and do not affect the P/A ratios. In aqueous solutions, addition of dioxane increases both rates and P/A ratios. Micelles of hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide; CTAB) and 3-(N,N-dimethyl dodecyl ammonium)propane-1-sulphonate (SDP) catalyse the alkaline hydrolysis of OCP and DCP and increase the yield of pyridone with BCP, OCP and DCP. In micellar CTAB and SDP the attack of OH- on RCP occurs almost exclusively at the 4-position of the pyridinium ring. Sodium dodecyl sulphate micelles inhibit the reaction and produce small changes in the P/A ratio. The regiochemical selectivity produced by micelles, leading to a preference for the attack of OH- at the pyridinium ring, was rationalized in terms of the low effective dielectric constant at the micelle-water interface.
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  • 54
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    Structure, topological electron density analysis and aromaticity of 4-heterosubstituted methylenecyclopropenes: X= X=CH2, NH, O, SiH2, PH and S (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 242-250 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of a series of heterosubstituted methylenecyclopropenes and methylenecyclopropanes were optimized at the HF/6-31G* level. All methylenecyclopropenes are planar except for the silicon analogue, which is bent at both C-3 and Si. The planar silicon structure is a transition state. The relative aromaticity of these compounds were evaluated using the C-1—C-3 bond length, the integrated charge on C-3 and the heteroatom, and delocalization energy. Second-row systems have slightly larger delocalization energies than their first-row counterparts, owing to their larger polarizability. Using these criteria, methylenecyclopropene and the silicon analogue are not aromatic and the N, O, P and S analogues are moderately aromatic. The planar silicon analogue is antiaromatic and bends from planarity to reduce this antiaromaticity.
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  • 55
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    Kinetics and mechanism of the alcoholyses of ethyl fluorosulphate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 251-259 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alcoholyses of ethyl fluorosulphate in methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and n-pentyl alcohols in the initial concentrations and temperature ranges of (1-10) 10-3 M and - 15.00 to 22.00 °C, respectively, were studied. The reactions follow pseudo-first-order kinetic laws up to at least ca 75 per cent ester conversions. At 10°C the experimental rate constant for ethanolysis is similar to that of ethyl triflate but much smaller than for its hydrolysis. The reactivity of the ester is ca 104-105 times higher than that of alkyl halides and benzenesulphonates. In alcohol-benzene and alcohol-acetone mixtures the ΔH≠ and ΔS≠ activation parameters are only slightly affected by the media composition. The effect of the ‘lyate ion’ on the kinetics of these reactions were investigated and the effects of changes in the dielectric constant of the media were evaluated. It is concluded that the alcoholyses of the ester fulfil the requirements for predominant SN2-type mechanism, where the reaction ground states are more polar than the corresponding transition states.
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    NMR study of polycrystalline azoles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 271-276 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polycrystalline pyrazole, imidazole and benzotriazole were investigated by 1H and 2H NMR spectroscopy. In addition to the usual broad line of the 1H NMR signal due to the dipole-dipole interaction, a significantly narrowed component (δν = 1-2 kHz) of a complex triplet structure was detected in all three compounds. To interpret this observation, a mechanism with virtually complete averaging of the dipole-dipole interaction for a small part of the sample protons is suggested. The mechanism is based on proton interaction with the unpaired electron of a short-lived radical of the type Az· or (H-Az·-H).
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  • 57
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    Gas-phase acidity of some α-keto aldoximes: Experiment and theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 285-292 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Experimental gas-phase acidities of 2-oxopropanaloximes, XCH2COCH=NOH (X = H, CH3S, CH3SO, CH3SO2; compounds 1-4), were determined by Fourier transform ion cyclotron resonance (FT-ICR) spectrometry. The values are δ Gacid° = 1401, 1381, 1360 and 1351 kJ mol-1 for 1, 2, 3, and 4, respectively. Molecular orbital calculations using the semi-empirical AM1 method provided information on the geometry and relative energy of neutrals species 1-4 and their conjugate bases, together with charge distributions and entropies of deprotonation. It is demonstrated that the proton abstraction occurs preferentially at the oxime function; the formation of an enolate as a conjugate base is unfavourable by 70-140 kJ mol-1. The large variation of the gas-phase acidities for 1-4 is explained in terms of the field/inductive empirical substituent constant σF. The variation of solution acidities appears to be comparatively strongly attenuated. This attenuation is attributed mainly to charge delocalization in the anion, which was confirmed by charge density calculations.
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  • 58
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    Depurination of (dien)Pt(II) complexes of purine deoxyribonucleosides. Comparison with the effects of (dien)Pd(II) ion complexing (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 301-309 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: First-order rate constants for the hydrolytic depurination of 2′-deoxyinosine and its various (dien)Pt(II) ion complexes were measured over the acidic pH range. The rate profiles obtained indicate that the uncomplexed nucleoside and its N1-(dien)Pt(II) complex are depurinated via mono- and di-protonated species, whereas the N7-(dien)Pt(II) and N1, N7-di(dien)Pt(II) complexes exhibit significant spontaneous hydrolysis, which competes with a markedly retarded acid-catalysed reaction. Rate constants for the various partial reactions were calculated and the results were employed to explain the effects that (dien)Pd(II) ion exerted on depurination rates of the same compounds. Similar measurements were carried out with the N1, N7-di(dien)Pt(II) complex of 2′-deoxyadenosine in order to further the understanding of the previously reported rate-enhancing effect of (dien)Pd(II) ion on the depurination of 2′-deoxyadenosine.
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  • 59
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    Crystallographic studies of intra- and inter- molecular interactions. Part VI. Crystal and molecular structure of N,N′-dimethyl-N′-phenylsulphonylformamidine. Equalization of CN bond lengths in the amidine fragment as a result of substituent effects due to push-pull (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 331-335 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structure of N,N-dimethyl-N′-phenylsulphonylformamidine is solved by direct methods and refined to R = 0.041 for 935 reflections, Equalization of CN bond lengths in the amidine fragment is discussed in terms of a push - pull effect operating between the N,N-dimethyl and SO2Ph groups. A significant role of the substituent at the functional carbon on the degree of π-electron delocalization on the NCN fragment is interpreted by use of the HOSE model.
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    Orientation of benzoic acid and terephthalic acid on an alumina surface and their reactivities observed by infrared spectroscopy (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 346-352 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The orientation of benzoic acid and terephthalic acid on alumina was ascertained by IR measurements. Benzoic acid was chemisorbed as a carboxylate anion with a vertical conformation of the benzene ring (0 〈 θ 〈 1.0) and as a mixture of the anion and the acid (1.0 〈 θ). Terephthalic acid was chemisorbed as a mixture of monocarboxylate anion (hydrogenterephthalate) and dicarboxylate anion (0 〈 θ 〈 0.3), as the monocarboxylate anion with a vertical conformation of benzene ring (0.3 〈 θ 〈 1.0) and a mixture of the monocarboxylate anion and terephthalic acid (1.0 〈 θ). The carboxyl group of expected hydrogenterephthalate adsorbed through the carboxylate anion on alumina (θ = 0.8 : 0.37 mmol g-1 alumina) readily reacted with dimethyl sulphate to form monomethyl terephthalate selectively.
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    Influence of some steric and electronic effects on the mechanism of SNAr reactions in dimethyl sulphoxide (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 367-371 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of 1-chloro- and 1-fluoro-2,4-dinitrobenzenes with aniline and 4-methylaniline in dimethyl sulphoxide are not base catalysed. When the nucleophile is 2-methylaniline, the reaction of the fluoro compound is base catalysed whereas that of the chloro compound is not. The reactions of 1-bromo-2-fluoro- and 1-bromo-2-chloro-3,5-dinitrobenzenes with both aniline and 2-methylaniline are not base catalysed. These results indicate that, in certain cases, the incidence or absence of base catalysis in aromatic nucleophilic substitution (SNAr) reactions in dipolar aprotic solvents results from an interplay of steric and electronic factors as they affect the magnitude of the (k2 + k3 [B])/k-1 ratio.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040608
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    Controlling factors determining addition and reduction products in the grignard reaction of substituted benzophenones, acetophenone and fluorenone with ‘EtMgBr’ (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 381-386 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Addition (Add.) vs reduction (Red.) products in the reactions of substituted benzophenones, acetophenone and fluorenone with ‘EtMgBr’ were compared in diethyl ether, 1,2-dimethoxyethane and tetrahydrofuran. Plots of log (Add./Red.) vs σ-values or the oxidation potentials of ketones showed characteristic upward curves depending on the polarity of the solvents. The results are discussed on the basis of both the combined effects of the stability of the monomeric radical ion pair and the dimeric radical ion pair derived from ketone and ‘EtMgBr’, and the well known Schlenk equilibrium of ‘EtMgBr’ in solutions.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040610
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    Micellar rate effects on reactions of hydroxide ion with phosphinate and thiophosphinate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 618-628 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cationic micelles of cetyltrimethylammonium chloride, bromide and mesylate (CTACl, CTABr, CTAOMs) speed reactions of OH- with phosphinate and thiophosphinate esters: Ph2PO.OPh (1a), Ph2PO.OC6H4NO2-p (1b), Ph(i-Pr)PO.OC6H4NO2-p (1c), Ph2PO.SEt (2a), Ph2PO.SPh (2b), (EtO)2PO.SPh (2c) and (EtO)2PS.OC6H4NO2-p (Parathion, 3). First-order rate constants go through maxima with increasing [surfactant]. The rate - surfactant profiles are fitted quantitatively in terms of a kinetic model that treats the distribution of OH- between aqueous and micellar pseudo-phases in terms of coulombic and non-coulombic ion-micelle interactions. Second-order rate constants at the micellar surface are lower than in water by factors that range from 0.035 for 1a to 0.7 for 1c. The thiophenyl derivative (2b) is more reactive than the corresponding phenoxy derivative (1a) and it is more reactive than the corresponding thioethyl derivative (2a). Parathion (3) is the least reactive substrate in both water and micelles.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610041006
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    Semiempirical SCF-MO calculations of kinetic isotope effects (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 635-638 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Carbon and deuterium kinetic isotope effects (KIEs) on the isomerization of methyl isocyanide were calculated by using the geometries and force fields obtained with MNDO, AM1 and PM3 Hamiltonians. These theoretical KIE values were compared with the corresponding experimental values. None of the hamiltonians used proved to be superior to any of the others. The best agreement for the carbon isotope effect was obtained by using the PM3 method; however, the deuterium isotope effect obtained by this method gave the poorest fit to the experimental data. The opposite is true when the MNDO Hamiltonian was used.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041008
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    Relationships between electronic substituent parameters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 629-634 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Core-electron energies for sulphur in a series of 2-substituted thiophenes have been used to investigate the relationship between electronic substituent parameters as developed by Taft and Topsom and by Charton. Initial- and final-state energies are analysed in terms of familiar substituent effects, such as field, delocalization and polarizability. The results show that the data correlate equally well with both sets of parameters and that there are many common features between the two methods. Both agree that resonance delocalization contributes significantly to the initial state, but has virtually no effect on the final state. In connection with this investigation we have also correlated the parameters for 31 substituents that are parameterized in the two approaches. The results of this more general study indicate some real differences between these and suggest that neither of the parameterizations incorporates all the electronic effects.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610041007
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    The effect of pressure on swern-moffatt oxidations (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 639-642 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of oxidation of cyclohexanol by dimethyl sulphoxide in conjunction both with acetic anhydride and with dicyclohexylcarbodiimide have been measured with variation of both temperature and pressure. Activation volumes were found to be -25 and -34 cm3 mol-1, respectively, and the absence of an α—d PKIE was noted. The reaction mechanism is discussed in the context of these values.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610041009
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041101
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  • 68
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    Short communication. Synthesis and properties of 4-cyano-1-(7-carboxyheptadecyl)pyridinium bromide: A probe of the ionic composition near the surface of positively charged micelles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 643-646 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 4-Cyano-1-(7-carboxyheptadecyl)pyridinium bromide (CCHP) was synthesized using standard procedures. The rates and product distribution of the reaction between OH- ion and CCHP are very similar to those previously obtained with alkyl-substituted 4-cyanopyridinium ions. The effect of hexadecyltrimethylammonium bromide micelles on the rate and product distribution of CCHP indicated that the cyanopyridinium ring of this compound is distal to the surface of the micelle. CCHP constitutes a probe for ionic composition in the vicinity of positively charged micelles.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610041010
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    Molecular mechanics (MM3) calculations on disulfides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 659-666 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An MM3 parameter set was developed for disulfides so as to permit the force field representation of these molecules with respect to geometries, including conformations, vibrational spectra and heats of formation.
    Additional Material: 13 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041103
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    Molecular Mechanics (MM3) calculations on sulfides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 647-658 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of eleven sulfide compounds including methanethiol, ethanethiol, dimethyl sulfide, ethyl methyl sulfide, di-tert-butyl sulfide, thiacyclopentane, thiacyclobutane, 5-thiabicyclo [2.1.1] hexane and 7-thiabicyclo [2.2.1] heptane have been calculated to agree with experimental data, along with the vibrational spectra of the first three of these. The heats of formation of 24 sulfides (including mercaptans) have also been calculated to agree with experimental data. In general, the force field for sulfides seems to be similar in accuracy with that for hydrocarbons.
    Additional Material: 19 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610041102
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  • 71
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    Protolytic equilibria of several 4-acyl-substituted 1-phenyl-3-methylpyrazol-5-ones in dioxane-water mixtures (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 667-674 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermodynamic proton ionization constants, TpKa, of several 4-acyl-substituted pyrazol-5-ones [acyl = trifluoroacetyl (HPMTFP), acetyl (HPMAP), hexanoyl (HPMHP)] were determined in various dioxane-water mixtures at 25 and 35 ± 0.1°C. The TpKa values were determined by glass-electrode potentiometry and refined by using the extensive weighted least-squares FORTRAN program TPKA. Both extrapolation and leastsquares methods were used to obtain TpKa values in pure water (0%). All three acyl derivatives are weak monoprotic acids with TpKa values between 2.5 and 3.9, following the order HPMTFP 〈 HPMAP ≤ HPMHP. The TpKa values do not vary linearly with the reciprocal of the dielectic constant of the medium; however, a plot of TpKa versus the mole fraction of dioxane, n2, is linear at a given temperature. Values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes associated with their protolytic equilibria were also calculated. Temperature, medium and substituent effects are briefly discussed.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610041104
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    Molecular and electronic structure of substituted bithiophenes (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 675-680 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Several substituted bithiophenes were prepared and their electronic structure studied by photoelectron spectroscopy and semi-empirical MO calculations. Comparison of the spectra of related molecules and analysis of calculated molecular geometries gave an indication of molecular conformations in the gas phase.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610041105
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    Structural studies of 1,3-di(N,N-dimethylformamidyl)-2-cyanoguanidine. The case of a strongly lewis basic nitrogen atom in the cyano group VIII. Crystallographic studies of intra- and inter-molecular interactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 689-692 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041107
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    Synthesis and NMR study of 5-furylmethylenehydantoins and 5-thienylmethylenehydantoins (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 681-688 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two series of 5-furylmethylenehydantoins and 5-thienylmethylenehydantoins were prepared and their 1H and 13C NMR spectra studied in comparison with those of compounds in the analogous 5-aryl- and 5-pyridyl- series. Differences in the effects of the aromatic, six- or five-membered heteroaromatic rings are discussed. Spectral analysis enables Z/E configurations to be assigned with confidence and conformational preferences to be qualitatively deduced. Some interesting solvent effects were also observed.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610041106
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041201
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    Topological aspects of chemical reactivity. Evans-dewar principle in terms of molecular similarity approach (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 701-705 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Evans-Dewar concept of aromaticity of transition states is given new theoretical support in terms of the similarity approach to chemical reactivity. The principal goal of this approach consists in providing a simple, chemically lucid justification for the legitimacy of the original intuitively formulated concept.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610041109
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  • 77
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    Z/E, photoisomerization of 5-arylmethylenehydantoins and 5-pyridylmethylenehydantoins (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 707-713 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Z/E photoisomerization of a series of 5-arylmethylenehydantoins and a series of 5-pyridylmethylenehydantoins by direct irradiation in methanol or ethanol solvent was investigated. The isomeric ratios at the photostationary state are dependent on the excitation wavelength and are related to the relative absorption coefficients of the two isomers. Measurements of quantum yields show the absence of quenching effects by oxygen or azulene, suggesting that triplet states either are not involved or are too short-lived for quenching to be observed. Preparative photoisomerization provides a route to the isomer which is not isolated or obtained only as a minor product by the usual method of synthesis.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610041202
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  • 78
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    Reactivity and reaction patterns of alkyl alkoxybenzene radical cations. Mechanistic pathways of the reactions between 2,5-DI-tert-Butyl-1, 4-Dimethoxybenzene and perfluorodiacyl peroxides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 1-6 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the reactions of 2,5-di-tert-butyl-1,4-dimethoxybezene (1) with different oxidants, the radical cation 1+. is always detectable by EPR. However, the observed reactivity of 1+. depends greatly on the oxidation systems employed. In S2O82-—Cu2+—HOAc and Ce4+—HOAc systems (HOAc = acetic acid), 1+. appears to have long lifetimes and does not undergo fragmentation spontaneously. In contrast, in (RFCO2)2—CF2CICFCI2 (F113) systems, the readily formed 1+. is short-lived, and large amounts of de-tert-butylation products have been isolated. Experimental results imply that the C—C bond cleavage involved in de-tert-butylation could be a consequence of an attack by perfluoroacyloxy radical on 1+. in their original solvent cage. The fact that addition of methanol to the reaction mixture leads to the formation of a large amount of tBuOCH3 (46%) and other evidence suggest that the tert-butyl group leaves as a carbocation. On the basis of these results, we conclude that the reactions of 1 with (RFCO2)2 are initiated by electron transfer and followed by a fast coupling of various radical species, namely, 1+. with RFCO2 or with RF in the solvent cage, to form σ-complexes which collapse or react with nucleophiles to yield the final products.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040102
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    Interactions between tetracyanoethylene and rauwolfia alkaloids (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 25-30 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Interactions of the Rauwolfia alkaloids yohimbine, corynanthine, ajmalicine and reserpine with tetracyanoethylene were investigated by UV - visible spectroscopy. The results suggest the instantaneous formation of blue complexes whose thermodynamic and spectroscopic properties closely resemble those of 1 : 1 charge-transfer complexes of tetracyanoethylene with indole derivatives. The complexes are stable when the piperidinic nitrogen atom of the alkaloids is protonated or methylated. In contrast, those of the free bases rapidly decompose to give the corresponding 3,4-dehydro derivatives. The kinetics of these reactions have been studied and a mechanism is proposed.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040106
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  • 80
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    Acid hydrolysis of 2-substituted 3-methyl-tetrahydro-1,3-oxazines: Simple models for tertiary glycosylamines (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 53-57 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydrolytic decomposition of 2-phenyl- and 2-isopropyl-3-methyltetrahydro-1,3-oxazines to 3-methylaminopropan-1-ol and appropriate aldehydes was studied by 1H NMR and UV spectroscopy in acidic solutions. The time-dependent spectra confirmed that the formation of the final products was preceded by an equilibration of three components, the two Schiff base intermediates and the starting material, of which the former produced a carbinolamine which in turn underwent heterolysis to the final products.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040109
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    Potentiometric and spectroscopic investigations of the aqueous phase acid-base chemistry of urazoles and substituted urazoles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 67-69 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aqueous-phase equilibrium acidity constants have been determined for urazole (1,2,4-triazolidine-3,5-dione), several substituted urazoles and other selected imides. Aqueous phase pKa values for urazole (5.8), 1-methylurazole (5.3), 4-methylurazole (5.7) and 1,4-dimethylurazole (5.3) indicate that (in water) the methyl group acidifies the urazole moiety when bonded to N-1 but has little effect on acidity when bonded to N-4. Aqueous phase pKa values for hydantoin (9.0) and 1-methylhydantoin (9.1) suggest that a 1-methyl substituent has little effect on the acidity of the imide proton present in hydantoin. These data, combined with aqueous phase pKa values for 1,2-dimethylurazole (7.5), a substituted urazole lacking amide protons, indicate that an amide proton in urazole (i.e. the proton bound to either N-1 or N-2 in urazole) is ca 1.5 pKa units more acidic than the imide proton (i.e. the proton bound to N-4). Changes in 13C NMR chemical shifts for the carbonyl carbon atoms present in variously substituted D2O phase urazoles, hydantoins, succinimide and their conjugate bases also confirm that amide N—H bonds found in urazole and 1-methylurazole are weaker, in a heterolytic acid - base sense, than imide N—H bonds.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040111
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    Activation and thermodynamic parameters of nucleophilic substitution. Reaction of alkyl halides with solid salts under phase-transfer catalysis conditions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 341-345 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The paper is concerned with the effect of temperature and the nature of a solid ionophore (MCl, where M = Li, Na, K, Rb or Cs) on the rate and equilibrium constants in the process of substitution of chlorine for bromine in hexyl bromide. The non-linearity of the log k vs 1/T, dependence is shown to be linked with a change in the physical meaning of the constants with temperature variations. This is attributed to the occurrence of a strong exothermic process consisting in the formation of a kinetically independent intermediate, that precedes the limiting stage. A mechanism including the formation of two stable ternary complexes coordinated on the solid-phase surface, one of which is structurally close to the starting reagents and the other to the final reaction products, is proposed. The observed activation energies, enthalpies of formation of the ternary complex and activation energies of the limiting stages for the forward and reverse substitution processes were calculated. Thermal effects of the substitution in the presence of various solid MCl species were determined from the thermodynamic data and observed activation energies for both reaction types. The substitution is shown to involve a limiting stage represented by a transition between the ternary complexes. A linear relationship between the activation energy for the limiting stage and the solid ionophore crystalline lattice was established, suggesting incorporation of the solid salt molecule into the transition reaction state. Potential energy changes in the course of substitution in the presence of the various MCl solid salts are discussed. The Bell - Evans - Polyani principle is shown to hold for these studies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040604
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    The nature of field effects and their fall-off with distance: The acidity of substituted quinuclidinium and bicyclooctylammonium ions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 353-360 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase acidities are reported for series of substituted quinuclidinium and bicyclo [2.2.2] octylammonium ions. Ab initio calculations are also reported for these equilibria at the STO-3G and 3-21G (for the quinuclidines) bases and can be used to extend the results. pKa values obtained for the bicyclooctylammonium ions are compared with previously reported results for the quinuclidinium ions. The results, as a whole, are considered together with similar values obtained for other saturated systems, to look at the varying transmission of field effects with distance. The falloff observed between the two series in the gas phase is considerably less than expected from simple electrostatics. In contradication with a recent claim, it is also shown that field effects, as measured by the parameter σF, give a good measure of the effect of the substituents in each series compared with a combination of resonance and electronegativity effects.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040606
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040701
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    Applicability of excess acidity functions in low-acidity media (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 413-419 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It is demonstrated that excess acidity functions do not correspond well to the pH scale in dilute solutions. Acidity constants, pKBH+, of seven moderately weak bases were determined; they were calculated by means of excess acidity functions, since the corresponding ionizations occur at acidity levels where the pH scale is partly used. The excess acidity method permitted extrapolation of measurements made in concentrated acids down to dilute solutions only up to about 5% (w/w) perchloric acid.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040704
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  • 86
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    Correlation of alkyl and polar substituents in the elimination kinetics of 2-substituted ethyl methanesulphonates in the gas phase (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 399-403 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the elimination of several polar 2-substituted ethyl methanesulphonates in the gas phase were determined in a static system, seasoned with allylbromide, and in the presence of at least equal amount of the freeradical suppressor propene and/toluene. The working temperature and pressure ranges were 290-360°C and 31°199 Torr (1 Torr = 133.3 Pa), respectively. The reactions are homogeneous, unimolecular, show a first-order rate law and take place according to the following equations: for 3-chloropropyl methanesulphonate, log k1 (s-1) = (12.01 ± 0.18) - (171.7 ± 2.1) kJ mol-1 (2.303RT)-1; for 4-chlorobutyl methanesulphonate, log k1 (S-1) = (11.78 ± 0.31) - (166.1 ± 3.5) kJ mol-1 (2.303RT)-1; for 3-methoxypropyl methanesulphonate, log k1 (s-1) = (11.50 ± 0.36) - (163.3 ± 4.0) kJ Mol-1 (2.303RT)-1; and for 2-ethoxyethyl methanesulphonate, log k1 (s-1) = (11.52 ± 0.37) - (167.3 ± 4.1) kJ mol-1 (2.303RT)-1. The present data together with those reported in the literature show that alkyl 2-substituted ethyl methanesulphonates give an approximate straight line when log k/ko vs σ* values (ρ* = -0.82 ± 0.088, intercept = 0.0084 ± 0.0209 and correlation coefficient r = 0.967 at 320°C) are plotted. However, polar substituents at the 2-position of ethyl methanesulphonates give rise to an inflection point at σ*(CH3) = 0.00 into another very good straight line (σ* = -0.29 ± 0.013, intercept = -0.0065 ± 0.0213 and r = 0.994 at 320°C). The mechanism of these reactions is considered to be heterolytic in nature, proceeding in terms of an intimate ion-pair intermediate.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040702
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  • 87
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    Correlations between empirical lewis acid-base solvent parameters and the thermodynamic parameters of ion solvation. Part II. Acidity parameters of cations and basicity parameters of anions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 439-448 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The parameters α, β and γ of the equation WΔsGf(MX) = αBKT + βET + γ were calculated and analysed for different salts (MX) in pure solvents and in non-aqueous solvent-water mixtures (S). Among 109 different equations, only 64 were taken for the final analysis since in the case of 38 equations the parameters BKT and ET were highly correlated. After a statistical analysis and normalization, on the basis of the coefficients α and β obtained, it was found that the ions analysed may be divided into three classes characterized by the different dependences of α on β: class I, H+, Li+, Na+, Rb +, Cs+, Me4N+, Cl-, Br- and I-, where αN = 1.074βN + 1.639; class II, Ag+, Cl-, Br-, I-, OAc-, SCN- and N3- where αN = 2.057βN + 2.147; and class III, Ph4As+, BPh4-, Ph4C and Ph4Ge, where αN is variable and βN is almost constant. Two main conclusions can be drawn out from the results obtained: the behaviour of ions considered as Lewis acids and bases reflects different hard-soft properties of the ions, and the behaviour of the Ph4As+ ion is different from that of BPh4-.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040706
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  • 88
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    AM1 studies on the intramolecular cyclization of ω-haloenolate anionsDetermination of reactivity by MO Theory, Part 72. For Part 71, see Ref. 1. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 449-458 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intramolecular cyclizations of ω-haloenolate anions, -CαH2—C(=O)—(CH2)n-3—CωH2—X with X = F, Cl and Br and n = 3-7, were investigated by the AM1 method. In most cases, cycloketone formation proceeds more favourably than cycloether formation, as predicted by the HSAB principle. The reactivity increases in the order X = F 〈 Br 〈 Cl for both processes, and for cycloether formation it is in the order n = 3 〈 4 〈 7 〈 6 〈 5 for all X but the relative order for n = 5 and 6 reverses in favour of n = 6 for cycloketone formation with X = Cl and Br. The softness of the acid centre, Cω, decreases for a harder X( = F) whereas it increases for a softer X( = Br). Thus the reactivity order with respect to X suggests that the softness of the base centres O and Cα belongs to the borderline class. The transition state (TS) structures indicate that the BEP principle is obeyed in all cases, and a less reactive process has a more product-like TS.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040707
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  • 89
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040101
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  • 90
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    Geometry of 2-benzopyrylium and pyrylium cations calculated by semi-empirical methods. Crystal and molecular structure of 1,3-dimethyl-6,7-dimethoxy-2-benzopyrylium perchlorate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 7-12 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: X-ray data on the crystal and molecular structure of 1,3-dimethyl-6,7- dimethoxy-2-benzopyrylium perchlorate show a good correlation with the geometry of the same cation calculated by the MINDO/3 and MNDO methods with total optimization of all geometrical parameters. The geometry of substituted pyrylium cations was determined by the MNDO and AM1 methods. On the basis of the data obtained, some effects of benzo [c] annelation are displayed for the 2-benzopyrylium cation in comparison with the pyrylium cation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040103
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  • 91
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    Micellar catalysis of the intramolecular aminolysis of the β-lactam antibiotic cephaclor (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 19-24 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate of intramolecular degradation of cephaclor, involving the attack of the amino group at C-17 (N-18) on the β-lactam carbonyl, was increased up to 50-fold by neutral (polyoxyethylene-23 lauryl ether; Brij) and zwitterionic [3-(N-dodecyl-N, N-dimethylammonium) propane 1-sulphonate; (SDP)] micelles. The rate of OH- attack on cephaclor was increased 2-3-fold by Brij and SDP micelles. In the absence of micelles the rate of intramolecular degradation of cephaclor increased by up to 2-fold by addition of organic solvents. Distance calculations, based on the crystal structure of the antibiotic, showed that the intramolecular degration can only proceed in a conformation involving a cis-amide bond (N-14 - C-15). Micellar catalysis of the intramolecular degradation process was proposed to be due to the stabilization of the reactive conformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040105
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  • 92
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    Development of a model to explain the influence of the solvent on the rate and selectivity of diels-alder reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 48-52 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvophobic and polarity parameters are used to explain the endo/exo selectivity of the reaction between cyclopentadiene and methyl acrylate. A good linear regression model with Sp and ETN is obtained. The existence of an intrinsic correlation between the Sp and ETN values, which makes the interpretation of the results difficult, is shown. A comparison of the results with other previously reported showed that the relative influence of Sp and ETN on selectivity depends on the nature of the reagents.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040108
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  • 93
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    Aggregation of amphiphilic molecules in water. I. α-phenylethylamine: 1H and 13C NMR study (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 58-66 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The concentration dependence of the 1H and 13C NMR chemical shifts in D2O and in CDCl3 solutions were determined for (±)-α-phenylethylamine (I). Aqueous solutions of (-)-I and (+)-I, 50% enantiomerically enriched in (-)- and (±)-2, 2, 2,-trifluoro-1-phenylethanol and the (+)- and (-)-N-formyl derivatives of I, were also studied. 1H nuclear Overhauser enhancements were used to check the conformations of the solutes at various concentrations and 1H T1 values were used to monitor the changes in molecular tumbling in solutions. The results are interpreted in terms of a spontaneous aggregation of solute molecules in water, with the possible determination of the critical micelle concentration. The time-dependent splittings in the 1H NMR spectra suggest further, more detailed, studies of the structures of the aggregates and the possibility of chiral recognition in water.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040110
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  • 94
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    Evaluation of solvent effects on the dissociation of aliphatic carboxylic acids in aqueous N,N-dimethylformamide mixtures according to the scaled particle theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 87-95 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The standard Gibbs energies of transfer, ΔGt° from water to water-N,N-dimethylformamide mixtures for the dissociation process of several organic acids (formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids) obtained from the pKa* values are discussed in terms of the extended Scaled Particle Theory from quantum mechanical calculations in order to estimate the cavity and electrostatic contributions. The residual energy term was correlated with the hydrogen bond acceptor density and the Kamlet-Taft β parameters. The main contribution to ΔGt° was due to dipolar and specific interactions.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040204
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  • 95
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    Electronic Resource
    The 11C/14C kinetic isotope effect method. The 11C/14C kinetic isotope effect in the SN2 reaction of N,N-dimethyl-p-toluidine with labelled methyl iodide (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 77-86 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Methodological aspects of the determination of 11C/14C kinetic isotope effects (KIEs) were investigated using the reaction of N, N-dimethyl-p-toluidine with labelled methyl iodide in methanol at 30 °C as model system. The primary 11C KIE was determined to be 1.202 ± 0.008 for this reaction. The isotope effect was determined by a one-pot technique based on liquid chromatographic fractionation of the reactant and product followed by liquid scintillation counting of the 11C and 14C radioactivity in these fractions. The KIE value obtained agrees well with the value predicted from a previously determined 12C/14C-KIE for the same reaction. Theoretical model calculations of both carbon KIEs were performed using the BEBOVIB IV program. Transition-state models ranging from reactant- to product-like were employed in the calculations, and three different reaction coordinate models with more or less pronounced Walden inversion of the methyl hydrogens were investigated.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040203
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  • 96
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    Electronic Resource
    Cross-interaction constants as a measure of the transition state structure. Part 15. Kinetic isotope effects in the SN2 reactions of 2-phenylethyl derivatives with deuterated aniline nucleophiles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 101-106 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic isotope effects (KIE) were determined for the reactions of 2-phenylethyl and 1-methyl-2-phenylethyl benzenesulphonates with deuterated aniline nucleophiles in acetonitrile at 65.0 °C. The results are in good agreement with the transition state (TS) structures proposed based on the sign and magnitude of the cross-interaction constants, pxz, between the substituents in the nucleophile (X) and the leaving group (Z). In the reactions of 2-phenylethyl derivatives, all three reaction pathways, kr, kt and kΔ, were found to be contributing competitively; the inverse secondary KIE observed with a stronger nucleophile changed into the primary KIE with a weaker nucleophile owing to the predominant contribution of the four-centre TS in the kf path. For the reactions of the 1-methyl-2-phenylethyl series, the kr path played a major role, the contribution from the front-side nucleophilic attack, kf, being negligible. In both reaction series, the aryl participation was important for the p-CH3O-substituted substrate.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040206
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  • 97
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    Addition of hydroxylamine to cyclohexanone and bicyclic ketones. Steric, electronic and hydrogen bonding effects on the general mechanism of addition of amines to carbonyl compounds (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 107-112 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three different types of pH-rate profiles were observed for the addition of amines to carbonyl compounds, depending on the relative predominance, at weakly acidic pH, of either a concerted or a stepwise mechanism. The predominant mechanism depends on the basicity of the amine and the mutual equilibrium affinity for adduct formation between the carbonyl compound and the amine. The reaction of hydroxylamine with cyclohexanone and bicyclic ketones was studied in order to examine the roles of steric and electronic effects in this mechanism. Cyclohexanone and 3-chlorobicyclo [2.2.1] heptan-2-one exhibit the profile expected for a single change in the rate-determining step with increasing pH from uncatalysed attack of the amine on the carbonyl group to hydronium ion-catalysed dehydration of the carbinolamine. In contrast, both bicyclo [2.2.1] heptan-2-one and bicyclo [2.2.2] octan-2-one show an unexpected profile with two negative breaks and five kinetically significant regions. This profile is explained by stabilization of the zwitterionic intermediate T± by intramolecular hydrogen bonding, leading to the formation of the carbinolamine by a stepwise mechanism at weakly acidic pH.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040207
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  • 98
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    Crystal and molecular structure of pyrylium salts. IV. Crystal and molecular structure of 2,6-diphenyl-4-(4-carboxyphenyl)pyrylium perchlorate. Interrelations between structural parameters due to substituent effects (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 121-124 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structure of 2,6-diphenyl-4-(4-carboxyphenyl)pyrylium perchlorate was solved by x-ray diffraction, yielding structural parameters of high precision (estimated standard deviations for bond length ≤ 0.5 pm, for bond angles ≤ 0.2°). Comparison with other 4-substituted derivatives of 2,6-diphenyl-4(4-carboxytphenylpyrylium) perchlorate shows regularities in the variations of structural parameters following classical views of substituent effects.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040209
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  • 99
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    Structure and dynamics of dicyandiamide: A theoretical study (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 125-134 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio MO methods have been used to study the structures and energetics of dicyandiamide, [(NH2)2C=N—C≡N], its isomers, protonated species, radical anions, transition structures for internal conformational change and transition structures for isomerization. Structures were optimized at the HF/STO-3G, HF/3-21G and HF/6-31G* levels; selected barrier heights for smaller analogues were also computed at the MP4SDTQ/6-31G* level. The most stable isomer of dicyandiamide has the cyano group on the imine nitrogen [1, (NH2)2C=NC≡N]; the other isomer [2, HN=C(NH2)NH—C≡N] lies 12.8 kcal mol-1 higher. Inversion at the imino nitrogen proceeds by a linear, in plane process with a barrier of 32.5 kcal mol-1. The amino rotation barriers are 19 kcal mol-1 (single NH2) and 40 kcal mol-1 (both NH2 in a conrotaory or a disrotatory fashion; if the NH2 groups are allowed to pyramidalize the disrotatory barrier drops to 20 kcal mol)-1. Protonation occurs preferentially on the imine nitrogen (PA = 219.7 kcal mol-1 for 1); the proton affinities PA of the amino nitrogens are 25-30 kcal mol-1 lower. Isomerization between 2 and 1 would go via a 1,3-sigmatropic hydrogen shift, but the barrier is high (48.3 kcal mol-1); protonation reduces the hydrogen shift barrier by ca 15 kcal mol-1. However, the most likely mechanism for isomerization involves protonation of the imine nitrogen in 2 followed by deprotonation of the cyano-substituted nitrogen to form 1, circumventing the energetically costly 1,3-sigmatropic hydrogen shift. When an electron is transferred to dicyandiamide, a sizeable fraction of the resonance stabilization of the guanidine moiety is lost.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040302
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  • 100
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    The grignard reaction of α-diketones. Radical intermediates as the determinant of carbon- and oxygen-attacked products (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 158-162 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Although carbon (normal)- and oxygen (abnormal)-attacked products are usually afforded in the Grignard reaction of α-diketones, the relative ratio of the two are strongly dependent on the structure of the Grignard reagents. The product-determining factors are discussed on the basis of the intermediate radicals formed from α-diketones and Grignard reagents.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040306
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