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  • 1985-1989
  • 1980-1984  (84)
  • 1915-1919
  • 1982  (84)
  • Biochemistry  (84)
  • 1
    Electronic Resource
    Electronic Resource
    Glycosaminoglycans (GASs) in human cerebral tumors (1982)
    Springer
    Acta neuropathologica 58 (1982), S. 115-119 
    Details
    ISSN: 1432-0533
    Keywords: Biochemistry ; Cerebral tumours ; Electrophoresis ; Glycosaminoglycans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary GAG electrophoretic pattern and concentration have been studied in 38 human cerebral tumors and in specimens of normal nervous tissue. Gray matter had higher total GAG concentration and higher CA to HA ratio than white matter. In both, DS was present in very small amount whereas HS represented 15% of GAGs. All benign gliomas displayed the same electrophoretic pattern and contained more GAGs than normal nervous tissue. Dermatan sulfate was detected in malignant gliomas, as well as in other oncotypes, due to their mesodermic component. Ependymomas were particularly rich in HS and meningiomas were poor in HA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00691651
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of aromatic retinoid on non-keratinizing (intestinal) epithelium: Biochemical and morphological studies (1982)
    Springer
    Archives of dermatological research 273 (1982), S. 85-90 
    Details
    ISSN: 1432-069X
    Keywords: Aromatic retinoid ; Intestinal epithelium ; Morphology ; Biochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Doses of 3 mg/kg Ro 10-9359 (in arachis oil) were daily administered to adult female Wistar rats by gastric tube for a period of 10 days. Control animals received corresponding quantities of arachis oil only. The body weight of all rats was registered daily. Samples of jejunum and ileum were processed for quantitative histochemical analysis of neutral α-glucosidase kinetics and for three-dimensional evaluation of the mucosal architecture. In addition, mucosal scrapings were prepared from these intestinal segments, and the specific sucrase activity was determined. For each animal data were pooled and analyzed by Wilcoxon (Wn) test. Body weight and all registered parameters in the jejunum of treated animals remained unchanged as compared to the controls. In the ileum, however, we found under aromatic retinoid an increase of sucrase activity (P=0.02) and of mucosal surface per unit serosal area (P〈0.05). The hydrolytic activity of neutral α-glucosidase (V max) showed a clear trend to increase at both the villus base and apex, whereas the apparent substrate affinity (K m ) remained unaltered. Our results show that, in closes of 3 mg/kg/day, aromatic retinoid induces (1) an increase in mucosal surface area, apparently due to hyperproliferation of the absorptive epithelium in ileum, which could facilitate its absorptive capacity and (2) an increase of specific sucrase activity, which could result in an enhanced carbohydrate assimilation. These findings indicate that Ro 10-9359 in addition to its effects on keratinizing epithelia exerts a distinct influence on the structure and function of the intestinal epithelium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00509030
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  • 3
    Electronic Resource
    Electronic Resource
    Theory of lone pairs. IV. Molecular ion hole states of ten-electron hydrides. Molecular ionization potentials and proton affinities by direct SCF calculations (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 14-22 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Closed-shell SCF calculations on the ground states and direct SCF calculations on the ionized doublet states were carried out for a series of ten-electron hydrides. The correlation of ionization potentials with the degree of protonation and the nuclear charge has been studied for hole states derived from excitation out of both the core and valence molecular orbitals. Calculated proton affinities of the ground states and hole states derived from a given symmetry orbital show a similar trend to that of the ionization potentials.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030104
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  • 4
    Electronic Resource
    Electronic Resource
    Pitfalls in the use of the torsion angle driving method for the calculation of conformational interconversions (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 40-46 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Several deficiencies and potential sources of error in the torsion angle driving method, the approach employed most frequently for the simulation of conformational interconversions, have been studied. A general explanation of the observed effects is given in terms of the energy surface and of the effects brought about by “side valleys.” Several examples of molecular mechanics calculations of conformational interconversions, among them the cyclohexane ring inversion, illustrate the problems.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030108
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  • 5
    Electronic Resource
    Electronic Resource
    An Ab initio study on the conformations of protonated, neutral, and deprotonated amidine (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 62-68 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio SCF molecular orbital calculations have been performed to ascertain the conformational preferences of protonated, neutral, and deprotonated amidine [HC(=NH)NH2], using the 3-21G split valence basis set. The states of eight stable species, eight transition states, and four higher-order saddle points have been determined by complete geometry optimization utilizing analytic energy gradient techniques. Protonation at the amidine =NH is preferred over the -NH2 site by 37.1 kcal/mol. Neutral amidine has rotational barriers of 9.6 and 11.7 kcal/mol for the HN=CN cis and trans isomers, respectively, while all the stable HC(NH2)2+ and HC(NH)2- species possess torsional barriers larger than 23 kcal/mol. There is, however, essentially free C - N single-bond rotation in HC(=NH)NH3+, the calculated barriers being 0.7 and 1.8 kcal/mol for the cis and trans HN=CN isomers, respectively.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030111
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  • 6
    Electronic Resource
    Electronic Resource
    Three-Electron bonds. II. SS and SCL three-electron bonds (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 112-116 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio molecular orbital calculations are reported for the H2SSH· and H2SCl· radicals and for the H2SClH+· radical cation. The two neutral species are found to be very weakly bound van der Waals' complexes, whereas the H2SClH+· radical cation is bound by 11.9 kcal mol-1 at MP2/4-31G. The importance of charge in σ* radicals is discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030116
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  • 7
    Electronic Resource
    Electronic Resource
    A quantum mechanical test of diophantine methods (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 117-124 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A blend of Haselgrove's method and the biased selection method for evaluating multidimensional integrals was tested. The results were mixed. The error estimate varied from being proportional to 1/N when N was less than ca. 60,000 to being proportional to 1/√N when N was greater than 60,000. Also, for N greater than 60,000, the error estimate was one-half the error estimate given by biased selection alone. These numbers should be compared with the 10,000 points used to find an optimum set of Haselgrove's parameters. It is reasonable to expect that if 100,000 points were used in the optimization of Haselgrove's parameters that the above results would be found with 60,000 replaced by 600,000.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030117
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  • 8
    Electronic Resource
    Electronic Resource
    Spherically symmetric axial Gaussian lobe 3d and 4f orbitals (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 130-134 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The axial Gaussian lobe orbital (AGLO) representations of 3d and 4f orbitals proposed by LeRouzo and Silvi have been angularly optimized to ensure spherical symmetry of filled 3d and 4f shells. The functions have been tested on the hydrogen atom in the presence of high quality s and p basis sets and found to provide excellent minimal Gaussian representations of polarization functions. Exact orbital degeneracy is not obtained within each shell, however. Tabulated values are given to allow arbitrary scaling of the 3d and 4f lobe mimic orbitals.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030203
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  • 9
    Electronic Resource
    Electronic Resource
    Thermochemical data from ab initio calculations. I. Estimation of SCF energies for augmented basis sets and Hartree-Fock limit energies (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 154-164 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A procedure is outlined which allows an estimation of molecular energies both for a finite basis set including polarization functions and for the Hartree-Fock limit. It is shown that the orbital error of a given minimal basis is covered to a certain relatively constant percentage by an augmented basis set calculation. Thus an improvement factor Qav can be determined by analyzing the corresponding results of small molecules where reasonable estimates of HF limit energies can be taken from the literature. For a combination of Pople's STO-3G and 6-31G* basis sets Qav turns out to be 0.955.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030206
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  • 10
    Electronic Resource
    Electronic Resource
    MINDO/3 Calculation of carbocation heats of formation (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 208-213 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Heats of formation calculated by MINDO/3 are reported for 42 carbocations for which experimental heats of formation have been published. Errors associated with these calculations can be large, with an overall range of ±13 kcal/mol. Correction of systematic errors in the MINDO/3 calculations by means of hydrocarbon models and isodesmic relationships results in a reduction in the range of errors to ±8 kcal/mol. Comparison with experimental heats of reaction of hydride transfer equilibria minimizes experimental errors and gives an average absolute error of 2 kcal/mol with a range of ±3 kcal/mol.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030211
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  • 11
    Electronic Resource
    Electronic Resource
    Fast semiempirical calculations (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 227-228 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Most quantum chemists regard semiempirical methods as ephemeral and computationally cost efficient. For this reason, an article dealing with computational efficiency of semiempirical methods is probably very unfashionable. However, experience at a big computer installation, shared by ab-initio and semiempirical quantum chemists shows that the second group actually consumes more computer time than the first. Obviously, the greater size of the molecules in semiempirical calculations outweighs the inherent efficiency of these methods. The present article describes a simple method for accelerating SCF-type semiempirical methods.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030214
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  • 12
    Electronic Resource
    Electronic Resource
    An open-ended self-consistent field method. A simulation of a molecular orbital technique for small memory computers (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 260-264 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The steps in a nonconventional algorithm for self-consistent field calculations are outlined, and calculations on cumulenes are given to demonstrate the convergence properties of the method. The approach is essentially open ended and is likely to be cost effective on computer systems with minimal core.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030218
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  • 13
    Electronic Resource
    Electronic Resource
    An introduction to PASCAL for scientists, James W. Cooper (wiley-interscience, New York, 1981) (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 273-273 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030221
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  • 14
    Electronic Resource
    Electronic Resource
    MNDO Calculations of silicon-containing molecules (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 445-450 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A comparison is made of MNDO and MINDO/3 calculations for saturated silicon-containing molecules, and with experimental values, for heats of formation, molecular geometries, charge distributions, and ionization potentials. Except for bond angles, it is found that with the published parameter values the MINDO/3 program gives more reliable results than MNDO. For unsaturated molecules, a comparison of bond lengths and stabilities of Si multiple bonds as given by the two programs and ab initio methods is made, and large discrepancies between predicted structures are pointed out. Some reasons for the dicrepancies are discussed.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030320
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  • 15
    Electronic Resource
    Electronic Resource
    The structure and stability of the acetylene dication (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 468-470 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The dication C2H22+ has been investigated by ab initio molecular orbital theory. It is found to have a linear (D∞h), structure with a triplet (3σ-g) ground state. Deprotonation to C2H+ is exothermic by 9.8 kcal/mol, but this process is hindered by a large barrier of 65 kcal/mol.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030403
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  • 16
    Electronic Resource
    Electronic Resource
    Conformational study of protonated, neutral, and deprotonated formamide (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 477-485 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Neutral, protonated, and deprotonated formamide isomers were studied at the 3-21G SCF level with complete geometry optimization. Ten stable structures, ten first-order saddle points, and three second-order saddle points (conformational maxima) are reported. [Total energies are reported in hartrees (1 hartree = 627.51 kcal/mol = 2625.5 kJ/mol) and energy differences are reported in kJ/mol (1 kJ/mol = 0.239 kcal/mol).] Rotational barriers and proton affinities are discussed and compared to isoelectronic amidine species.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030405
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  • 17
    Electronic Resource
    Electronic Resource
    The structure and acid-base properties of methyl and silyl amines and phosphines: An ab-initio SCF study (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 495-506 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The structures of the methyl and silyl amines and phosphines and their ions have been calculated using ab-initio SCF theory and the 3-21G basis set. The computed structures give excellent agreement with the available experiment data without the inclusion of d functions, with the exception of (SiH3)2N- and the isoelectronic molecules (SiH3)2O and (SiH3)2C2- where d functions are essential. The observed trends in computed basicities and acidities are reproduced by the calculations.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030407
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  • 18
    Electronic Resource
    Electronic Resource
    A nonelectrocyclic path from the cyclobutene cation radical to the 1,3-butadiene cation radical (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 548-551 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conversion of the cyclobutene cation radical to the 1,3-butadiene cation radical has been studied using MINDO/3 and ab initio SCF MO methods. Not only smooth electrocyclic but also stepwise, non-electrocyclic routes were considered. Both calculational methods agree that the preferred reaction path is a novel nonelectrocyclic one proceeding through an intermediate “cyclopropylcarbinyl cation radical.” The quantitative agreement in the activation parameters calculated by the two methods is excellent. The proposed intermediate also provides an attractive explanation for the mass spectrometric fragmentation patterns of the cyclobutene and butadiene cation radicals.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030411
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  • 19
    Electronic Resource
    Electronic Resource
    Masthead (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030401
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  • 20
    Electronic Resource
    Electronic Resource
    Orbital topology. III. Orbital mapping of unsymmetrical molecules. A survey of the thermal ring opening of isoelectronically substituted cyclobutenes and benzocyclobutenesA brief discussion of these results has been presented at the American Chemical Society, 180th National Meeting, Las Vegas, August 25, 1980, abstract ORGN 043. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 436-444 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Orbital mapping analysis based on CNDO/2 molecular orbitals has been used to survey the thermal ring-opening isomerizations of cyclobutenes and benzocyclobutenes. Isoelectronic substitutions within the molecular framework of cyclobutene (e.g., CH2 replaced by CH-, OH+, NH, NH2+) result in ground-state orbital correlations via both conrotatory and disrotatory pathways in several cases, in contrast to the parent hydrocarbon conrotatory stereochemistry. The results substantiate the heteroatom effects previously revealed by orbital mapping for the disrotatory thermal isomerizations of isoelectronic Dewar benzenes. Qualitative patterns, such as nodal shifts in the butadiene π orbital, are discussed in relation to the mapping correlations. The isoelectronic benzocyclobutenes give ground-state orbital correlations via conrotatory pathways only, which suggests that delocalization may reduce the heteroatom perturbation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030319
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  • 21
    Electronic Resource
    Electronic Resource
    Conformational analysis by energy embedding (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 471-476 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The distance geometry approach to conformational calculation has been shown to be very effective at producing large molecular structures satisfying many given, long-range constraints on the interatomic distances. I now present a significant extension of the method that handles strictly geometric constraints as well as before while also locating conformers of very low energy. The main feature of the algorithm is a projection of the molecule from a low energy conformation in a high dimensional space to three dimensions in such a way as to perturb the energy as little as possible. Tests of the method on very small systems with simple energy functions completely explored by independent means show that the global minimum of energy is sometimes attained. In every case the final energy is very low, and geometric constraints are completely satisfied.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030404
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  • 22
    Electronic Resource
    Electronic Resource
    Thermodynamical properties and structural data of radicals calculated by MNDO-UHF (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 486-494 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The MNDO-UHF method has been applied to a large number of organic and inorganic radical species. The obtained results demonstrate that thermodynamical data as well as their equilibrium structures are in reasonable agreement with experimental findings.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030406
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  • 23
    Electronic Resource
    Electronic Resource
    An ab initio study of the relationship between the O—H bond length and the harmonic and anharmonic stretching force constants for planar molecules containing C—OH, N—OH, and O—OH groups (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 512-524 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The O—H bond length and the quadratic, cubic, and quartic stretching force constants, calculated ab initio using the unscaled 4-31G basis set with full geometry optimization, are reported for 30 planar conformers of ten molecules contaning either the C—OH, N—OH, or O—OH group. The data are analyzed in terms of the general form of Clark's equation, and the power functions and exponential functions proposed by Herschbach and Laurie. In the case of the quadratic constants, significant trends are found in the values of the parameters depending on whether the O—H group is bonded to carbon, nitrogen, or oxygen, and whether it is non-hydrogen-bonded or involved in intramolecular hydrogen bond formation in four-, five-, or six-membered rings. Using data for diatomic molecules, O—H, and C—H bonds, and the C=O and C—C bonds in planar monosubstituted carbonyl compounds, the parameter dij in the power function equation for quadratic constants, which can be regarded as the distance of closest approach of the two nuclei, is shown to increase progressively along the series (i) diatomic molecule; (ii) similar bond in a polyatomic environment with one of the two atoms covalently bonded to a neighboring atom; (iii) as in (ii) but with the second atom hydrogen bonded; and (iv) with both atoms covalently bonded to neighboring atoms.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030409
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  • 24
    Electronic Resource
    Electronic Resource
    Improved SCF convergence acceleration (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 556-560 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An improved version of the direct inversion in the iterative subspace algorithm is developed. The method is significantly more efficient than the previous version, and is applicable to intrinsically divergent or slowly convergent cases. Comparisons indicate that the method is superior to the recently proposed quadratically convergent (QC-SCF) method of Bacskay.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/jcc.540030413
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    Electronic states and barriers to internal rotation in silaallenes (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 571-579 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The electronic states and barriers to internal rotation in allene (1a), 1-silaallene (2a), and 2-silaallene (3a) are investigated computationally using ab-initio molecular orbital methods. Planar geometries with two-, three-, and four-π-electron configurations have been considered as possible transition states (1b-3d). Structures have been optimized at the Hartree-Fock level with a small split valence basis set (3-21G) and higher level calculations with basis sets of split valence (6-31G) and split valence plus polarization function (6-31G*) quality include correlation energy estimates from Møller-Plesset second-and third-order perturbation theory. The electronic barrier to internal rotation in allene is estimated near 53 kcal/mol whereas the corresponding barriers in 1-silaallene and 2-silaallene are considerably smaller, ca. 35 and 20 kcal/mol, respectively. The transition states are predicted to possess bent geometries in all three molecules with open-shell singlet, three-π-electron configurations in 1 and 2 (1c, 2c) but a closed-shell singlet, two-π-electron configuration in 3 (3d).
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030416
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  • 26
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    Distance geometry and conformational calculations, G. M. Crippen. Research Studies Press, Chichester, New York, 1981, 58 pp. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 603-603 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030420
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  • 27
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    Masthead (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030101
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  • 28
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    On the OCS2 Singlet potential energy surfaceOxathiiranes Part VIII; for Part VII see ref. 1. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 23-27 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The reaction between atomic oxygen and carbon disulfide is predicted to lead to at least two primary products, which are the dithiiranone (1) and the oxathiirane-thione (2) and/or the carbon disulfide S-oxide (4). The possible intramolecular equilibria 1 ⇄ 2, 1 ⇄ 3, 2 ⇄ 4, and 2 ⇄ 5 as well as the fragmentations of the possible intermediates 1-5 have been studied theoretically within the semiempirical CNDO/B framework as conceivable ground-state reactions. On the basis of MO correlations and potential energy changes along the reaction paths, supplementary with previously reported experimental data, the single molecular transformations and the eventual product formations are discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030105
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  • 29
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    On computation of the topological resonance energy (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 28-36 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The topological resonance energy (TRE) model was introduced independently by the Zagreb Group (in 1975) and by Aihara (in 1976). Several practical obstacles arise in the computation of TRE. Ways to surmount them are pointed out. Descriptions of algorithms, optimizations, and the efficient computer program are presented. Possible numerical instability is discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030106
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  • 30
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    Ab initio studies of structural features not easily amenable to experiment. 17. The molecular structures of some strained cyclic hydrocarbons and estimates of their strain energies (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 53-61 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The molecular structures of tricyclohexane, norbornane, quadricyclane, and cubane were completely refined by standard ab initio force relaxation on the 4-21G level. The results can be used as a basis to interpret some contradictory experimental reports found in the literature and to establish some hitherto unobserved structural trends involving the C—C and C—H bond distances of the cases studied. Group Delta;E values for C—(H)3(C), C—(H)2(C)2, and C—(H)(C)3 (Benson's notation) derived from the total energies of the completely relaxed 4-21G geometries of a number of unstrained hydrocarbons are also listed. The values are used to estimate the strain energies of the systems studied and of the optimized 4-21G geometries of cyclopropane, cyclobutane, cyclohexane, and bicyclo (2.1.0)pentane. Cooperative effects in the strain energies are discussed.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030110
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  • 31
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    Computer generation of nuclear spin species and nuclear spin statistical weights (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 75-88 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article develops computer programs for computer generation of nuclear spin species and nuclear spin statistical weights of rovibronic levels. The programs developed here generate nuclear spin species and statistical weights from the group structures known as generalized character cycle indices (GCCIs) which are computed easily from the character table of the PI group of the molecule under consideration. Procedures are illustrated with examples.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030113
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  • 32
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    Masthead (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030201
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  • 33
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    Selectivity effects and hydrocarbon-chain growth during Fischer-Tropsch synthesis (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 135-139 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: It is well known that if the formation of hydrocarbons during Fischer-Tropsch synthesis occurs via the condensation polymerization mechanism, there is little hope for selectivity enhancement in the desired range of products. Recent data on low surface area model catalysts, where readsorption is unlikely, have shown that at low conversions, the product distribution obeys the condensation polymerization mechanism and the distribution of products is shifted to lower-molecular-weight hydrocarbons. We have used a computer simulation of the growth of hydrocarbon chains to obtain a picture of the catalyst surface under synthesis conditions. Such an approach could prove useful in distinguishing between various theoretical models. We have applied the simulation to compare the changes in selectivity when readsorption occurs and when it does not. The dynamic behavior of the reacting system which is obtained from the computer results has shown that selectivity to lower-molecular-weight hydrocarbons is a stronger function of the extent of reaction than the incorporation of readsorption into the chain growth mechanism.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030204
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    Thermochemical data from ab initio calculations. II. Total correlation energies, Schrödinger energies, and theoretical heats of formationFor Part I, see the preceding article in this issue. Abbreviations are used in the same manner as in Part I. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 165-177 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Bond correlation energies ∊(XY) have been derived by partitioning second-order Rayleigh-Schrödinger-Møller-Plesset (RSMP) correlation energies. Values of ∊(XY) depend on the type of bonding between atoms X and Y. They can be considered as comprising correlation energies of bond, lone, and inner-shell electron pairs of the group XY. Once a set of appropriate increments ∊(XY) has been obtained, it is possible to estimate unknown RSMP energies of larger molecules. This concept also can be used when estimating total correlation energies E(CORR). For this purpose e(XY) values have been derived from known E(CORR) energies of small molecules. It is shown that ∣∊(XY)∣ increments increase linearly with the number n of electron pairs of the group XY. The function ∊(n) becomes zero for n = 1/2 (one uncorrelated electron) and passes through -0.042 for n = 1, which is approximately the correlation energy of the bonding electron pair of H2 or a 1s inner-shell pair. With the aid of estimated E(CORR) and HF limit energies, Schrödinger energies and theoretical heats of formation of relatively large molecules are obtained.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030207
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  • 35
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    Configuration interaction (CI): Approximate inclusion of fourfold and threefold excitations, an application of knowledge engineering (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 191-207 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: It is shown that even the CPMET approximation for the contributions of fourfold excitations can be replaced by a more sophisticated method. Furthermore, an approximation is presented for the contributions of threefold excitations which are neglected in CPMET. Finally, it is described how the advantages of different CEPA methods can be united in a single CEPA scheme (called CEPA-U). The various approximations are discussed in terms of Slater determinants, and it is shown how the relatively large amount of details can be handled with the help of computer programs, i.e., how knowledge engineering can be successfully applied here.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030210
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  • 36
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    Evaluation of MINDO/3 calculated structures. III. Saturated acyclic compounds with chlorine, nitrogen, oxygen, or sulfurFor Part II see ref. 1. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 229-233 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Fifty-one structures have been calculated by the MINDO/3 method to evaluate the errors introduced by branching and by the presence of the heteroatom. The structures are evaluated by comparisons which reveal that the calculated ΔHf values reflect a bias because of the presence of the heteroatom. With two carbons or more in a chain attached to a heteroatom group, a linear relationship exists which makes possible the calculation of reasonably accurate ΔHf values for unbranched alcohols, primary or secondary amines, ethers, thioethers, thiols, and alkyl chlorides. Branching errors do not seem to be linearly related among the systems. Some errors in calculations of geometries are also discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030215
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  • 37
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    Effect of electron correlation on theoretical vibrational frequencies (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 234-250 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Theoretical HF/6-31G* (Hartree-Fock, 6-31G* basis set) and MP2/6-31G* (second-order Møller-Plesset, 6-31G* basis set) vibrational frequencies based on complete quadratic force fields have been obtained for a set of 36 one- and two-heavy-atom molecules comprising first-row elements for which experimental spectroscopic data are available. Frequencies calculated at the HF/6-31G* level are an average of 12.6% higher than experimental values. Partial treatment of electron correlation via the perturbation method of Møller and Plesset, terminated at second order, leads to a significant reduction in this error, although theoretical MP2/6-31G* frequencies are still larger than the experimental quantities by 7.3%. Part of the difference may be traced to the restriction of quadratic force fields, as comparison with experimental harmonic frequencies shows deviations of only 9.5% and 4.7% for the two levels, respectively. The calculated frequencies are used in conjunction with the corresponding theoretical equilibrium structures to obtain absolute molecular entropies, which may in turn be used to yield entropies of reaction. These latter quantities are generally in good accord with entropies derived using experimental structures and frequencies.
    Additional Material: 11 Tab.
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    URL: http://dx.doi.org/10.1002/jcc.540030216
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    Personal computers in chemistry, Peter Lykos, ed., Wiley, New York, 1981, 262 pp. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 273-273 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030222
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  • 39
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    Ab initio studies of structural features not easily amenable to experiment. 22. Structural aspects of a long-chain hydrocarbon (n-nonane) and a study of the transferability of electronic effects through C—C single bonds (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 269-272 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The molecular structure of the stretched form of n-nonane, as a typical long-chain hydrocarbon, was refined by geometrically unconstrained ab initio force relaxation on the 4-21G level. The C—C bonds and C—H bond distances in the interior of the hydrocarbon chain are found to be longer (by about 0.001 Å and 0.002 Å, respectively) than those near the end of the chain. Similarly, interior C—C—C bond angles are 0.4° larger than the terminal angles. The variation of structural parameters with distance from the molecular ends levels off after the second carbon atom, and the geometry of methylene is practically constant from C3 on. However, if one end of the system is perturbed by moving the inplane methyl hydrogen away from equilibrium, the resulting destabilizing electronic effects are transmitted through the C—C bond distance chain in such a way that significant perturbations are still experienced at C5. Molecular mechanics (MM2) gives a structure in which the small changes in bond lengths and angles with chain location are well reproduced.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030220
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    Planar and nonplanar vibrations of cytosineThis work was supported in part by NIH grant No. GM24443, NSF grant no. DMR-74-14367, and American Cancer Society grant No. IN17Q. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 305-316 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The formalism developed in the preceding article is used in a normal coordinate analysis of the pyrimidine base cytosine. The results of both planar and nonplanar vibrations are reported. The model yields 66 frequencies with an average error of about 6.5 cm-1 (ca. 0.5%). The vibrational modes are compared with experimental data and discussed in terms of potential energy distributions and Cartesian displacements. Two isolated low-frequency (near 200 cm-1) out-of-plane modes are predicted in the vicinity of where two such modes are believed to occur. In addition, the model has taken into account the observed coalescence of the torsional and wagging modes of the amino group upon deuteration of the amino group. Recent data from sulfur-substituted cytosine (2-thiocytosine) were useful in making assignments.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030305
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    A semiempirical formulation for the study of molecular interactions (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 329-334 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The coefficients of a 1/R expansion (containing long-range electrostatic interaction, medium-range electrostatic-induced dipole attraction, short-range dispersive attraction, and very short overlap interaction terms) have been determined, within a semiempirical approach, from the results of a priori calculations. The formulation has been applied to the study of the stable conformations of benzene complexes.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030307
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  • 42
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    Coupled calculations of vibrational frequencies and intensities. III. IR and Raman spectra of ethylene oxide and ethylene sulfide (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 354-362 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The experimental IR and Raman spectra of ethylene oxide have been reinvestigated with particular attention to the intensities. The absolute IR intensities have been measured for the gaseous state. The spectra have been simulated by using a normal coordinate analysis coupled with a CNDO determination of the intensities. The intensity calculation using polarization functions appears to be more reliable than the standard version. Furthermore, the force field has been extended for ethylene sulfide.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030310
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    Principles for a direct SCF approach to LICAO-MOab-initio calculations (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 385-399 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The principles and structure of an LCAO-MO ab-initio computer program which recalculates all two-electron integrals needed in each SCF iteration are formulated and discussed. This approach - termed “direct SCF” - is found to be particularly efficient for calculations on very large systems, and also for calcuations on small and medium-sized molecules with modern minicomputers. The time requirements for a number of sample calculations are listed, and the distribution of two-electron integrals according to magnitude is investigated for model systems.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030314
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    Strain energies of some bridgehead olefins as calculated with the MM2 force field (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 417-420 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The MM2 force field has been used to calculate the strain energies of a representative series of bridgehead alkenes, and the results compared to similar previous calculations using the MM1 force field. The new results roughly parallel the old ones, although the strain energy of a given compound is normally higher with MM2 than MM1. These differences are largely negated, however, when the OS (olefinic strain) value is considered.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/jcc.540030317
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    Mechanisms of conformational chirality inversion in bicyclo[4.2.1]nonan-9-one and bicyclo[4.2.2]decane as studied in two-parametric torsional energy surfacesPart 14 of a series, “Application of Potential Energy Calculations to Organic Chemistry.” part 13: E. Ōsawa and H. Musso, Top. Stereochem., 13, 117 (1982). (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 400-406 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: With the purpose of deciphering conformational inversion processes of typical mobile bicyclic molecules, torsional energy surfaces near the enantiomers of bicyclo[4.2.1]nonan-9-one (1) and bicyclo-[4.2.2]decane (2) were prepared using molecular mechanics with an improved two-bond drive technique. Inversion of 1 takes place most favorably via a Cs transition state with the tetramethylene chain over the ethano bridge [1B, ΔH± 6.1 (calculated) vs. 6.8 (observed) kcal/mol]. An alternative pathway involving a Cs local energy minimum (1C), in which the tetramethylene chain is bent over the carbonyl, has a barrier 2.4 kcal higher than 1B. The global energy minimum conformation of 2 has boat-chair cyclooctane and twist-boat cyclohexane rings (BCTB), and enantiomerizes into its mirror image (BCTB') via three intermediates: TCTB, CB, and TCTB'. The highest point in the proposed pathway, a saddlepoint CB, is calculated to lie 8.0 kcal/mol above BCTB (observed ΔH± 7.8 kcal/mol). The advantage of the two-parametric over the one-parametric torsional energy surface is discussed.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030315
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    On evaluation of the characteristic polynomial for large moleculesDedicated to the memory of Charles A. Coulson who appreciated the role of graph theory in chemistry and made contribution to the field at the time most of us were unaware of graph theory. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 421-435 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Existing schemes for evaluation of the characteristic polynomial of a graph suffer from limited practicality. Their application to large molecules inordinately increases the amount of labor. Here a procedure is outlined which is useful even for large molecules. It is based on a not widely known property of the collection of characteristic polynomials for Ulam's subgraphs, which, when added, give the derivative of the characteristic polynomial of the initial graph. The characteristic polynomials for Ulam's subgraphs are, as a rule, easier to derive due to the presence of many pending bonds in graphs of chemical interest. The last step requires an integration of a polynomial (which is a straightforward step) and determining the constant of integration, which represents the determinant of the adjacency matrix. The available methods for determing the additive constant (the determinant) are combinatorially much simpler than the initial task of finding all of the coefficients of the characteristic polynomial. The approach is illustrated on selected benzenoid hydrocarbons, nonbenzenoid, and nonalternant systems. Construction of the characteristic polynomials can be accelerated by considering auxiliary fragments and irreducible subgraphs separately and combining them in the final expression. Many auxiliary fragments allow their characteristic polynomials to be expressed in a closed form using recursive relations. The results for complex molecules can thus be written in a relatively compact form. Finally, the derivative of the characteristic polynomial, expressed in terms of selected auxiliary functions and irreducible components, can be integrated directly to give the result in terms of contributions signifying various fragments rather than as an explicit function of x.
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    URL: http://dx.doi.org/10.1002/jcc.540030318
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  • 47
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    Electronic Resource
    Quasi-one-dimensional systems and localized defects: Some results of the Green's matrix formalism (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 451-467 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The application of the self-consistent field (SCF) local-impurity formalism to quasi-one-dimensional systems is discussed. We describe a general procedure for an accurate numerical determination of the Green's function matrix elements of the unperturbed system. An application to a local impurity in a model chain with two orbitals per unit cell is reported. The changes in the charge-bond-order matrix and in local and total density of states due to the impurity are discussed with special emphasis on the changes at the critical points (van Hove singularities) at the band edges. The Green's matrix approach is used to reexamine long-range Friedel oscillations caused by an impurity in a strictly one-dimensional metal. The extent of the long-range tail of the perturbed charge density is in an inverse relation to the localization length of the impurity state: the stronger the perturbation the more localized is the bound state and the more extended are the oscillations in the charge distribution. The results for the model chain with two orbitals per unit cell indicate that the impurity-induced change in charge distribution may be locally screened by redistribution of the population of the on-site orbitals, therefore damping possible oscillations and leading to a faster decay than in strictly one-dimensional systems.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030402
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  • 48
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    Electronic Resource
    An improved description of lone pairs by a modified PCILO method (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 507-511 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The inadequate description of molecular systems involving lone pairs by the original PCILO method is analyzed on some examples. A modified PCILO version for the lone-pair description is proposed. The success of this method is represented in the same examples.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030408
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  • 49
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    Localized molecular orbital energies within the CNDO/BW formulation (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 552-555 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Localized molecular orbital (LMO) energies obtained from the canonical molecular orbital (CMO) energies and unitary transformation or from the matrix of the Fock operator and the LMOs are described. The results for water and ethylene are given, and compared with earlier work of Wilhite and Whitten.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030412
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  • 50
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    Electronic Resource
    Acceleration of convergence in Monte Carlo simulations of aqueous solutions using the metropolis algorithm. Hydrophobic hydration of methane (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 525-547 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Convergence problems encountered in the computer simulations of aqueous solutions are discussed. Solute-solvent radial distribution functions are shown to converge very poorly when the standard Metropolis Monte Carlo procedure is applied. To overcome this difficulty, several modifications are made in the Metropolis method. Optimum maximum step sizes are determined for simulations of liquid water. A scheme is employed for preferential sampling of both the solvent and the solute molecules. To test these modifications, a simulation is carried out for pure liquid water, treating a single water molecule as a “solute.” The convergence of the radial distribution functions is found to be accelerated significantly. A further test is made by simulating an aqueous solution of methane, consisting of one methane molecule (using the EPEN/2 potential for methane-water interactions) and 124 water molecules (using the MCY potential for water-water interactions). Again, the convergence of solute-solvent radial distribution functions is found to be accelerated. The computation of partial molar thermodynamic quantities, however, still suffers from convergence difficulties. This problem is discussed in detail. The EPEN/2 potential is found to yield structural and thermodynamic features of hydrophobic hydration that are consistent with available experimental and theoretical results for aqueous solutions of methane.
    Additional Material: 20 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030410
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    Ab-Initio studies on π-nonbonded and through-bonds interactions in n-alkanes, n-alkyl radicals, and polymethylene diradicalsPart 14 of the series, “MO Studies of Configuration and Conformation.” (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 565-570 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab-initio studies were conducted on quantitative aspects of π-nonbonded, σ-σ*, n-σ*, and throughbond interactions in R1CH2(CH2)N-1 CH2 R2, where R1 and R2 are H and/or nonbonding AO, n, and N = 2, 3, and 4. Geometrical preferences were found to depend both on π-nonbonding and bond-antibonding interactions, the latter being more important. Level orderings and energy splittings involved in the through-bond interactions of diradicals can be qualitatively predicted by examining the signs of the overlap between the n orbitals and a common vicinal σ* bond orbital, using simple orbital patterns and paying special attention to the “backside” tails of bond orbitals.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030415
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  • 52
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    A molecular packing analysis of some ferrous porphyrin complexes (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 588-592 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An analysis has been made of the applicability of various sets of nonbonded interaction potential parameters which do not consider hydrogen atoms explicitly, to represent molecular packing interactions in crystals of ferrous porphyrin complexes, which are models for deoxyhemoglobin. Ordered regions of the structures are well described, but disordered solvent or ligands cause difficulty.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030418
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  • 53
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    Computational study on the interaction of water with 2- and 3-hydroxypyridine and the corresponding pyridones (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 593-602 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: SCF-MO-LCAO ab-initio computations were carried out for the four tautomers 2-pyridone, 2-hydroxypyridine, 3-pyridone, and 3-hydroxypyridine interacting with a water molecule placed at different positions and orientations around each of them. The computed interaction energies were fitted by an analytical potential consisting of a 6-12 Lennard-Jones term plus a Coulombic one. The root-mean-square deviation of the fit is 2.5 kJ/mol. We report isoenergy contour maps for some important cross sections and obtain a qualitative trend of the solvation entropy, in agreement with available experimental data. The obtained potentials were used for Monte Carlo simulation of four clusters consisting of a tautomer molecule as solute and 50 water molecules, at 300 K. The problem of the transferability of fitting constants is also examined.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030419
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  • 54
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    An ab initioCI calculation of the triplet-triplet absorption spectrum of naphthalenePresented at the 16th Symposium for Theoretical Chemistry, Wildhaus, Switzerland, 7-11 September 1980 (Abstract A14). (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 1-5 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The triplet-triplet absorption spectrum of naphthalene (3B1g ← 3B2u; 3Ag ← 3B2u) was calculated using an ab initio method with a STO-3G basis set and moderately large configuration interaction. Eight bands were found in the region 18,000-45,000 cm-1 and compared with those of the experimental spectrum. The strongest band observed at about 44,000 cm-1 was assigned to a 3Ag ← 3B2u tansition. The excited triplet and singlet ground-state electronic charge distributions are compared.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030102
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  • 55
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    A systematic preparation of new contracted Gaussian-type orbital sets. VIII. MINI-1 and MIDI-1 sets for Ga through Cd (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 6-13 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Minimal contracted Gaussian basis sets are presented for Ga through Cd. Characteristically these Gaussian-based minimal sets give far better d orbital energies than those by minimal STO basis sets. These new basis sets were tested on Br2 for which a new benchmark calculation was also performed. The test result is satisfactory in that these basis sets produce good general agreement with the near Hartree-Fock calculation with respect to the molecular spectroscopic constants.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030103
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  • 56
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    The imposition of linear constraints upon eigenvalue problems (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 37-39 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A simple method of imposing linear constraints upon an eigenvalue problem is described that reduces the dimension of the problem by the number of constraints imposed. Several applications are outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030107
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  • 57
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    Studies in hydrogen bonding: Association within mixed dimers of water, methanol, ammonia, and methylamine using the empirical potential EPEN (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 47-52 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An empirical potential EPEN has been used to find the stable geometries and approximate hydrogenbond energies of the mixed dimers formed between molecules of water, methanol, ammonia, and methylamine. These results are compared with results in the literature obtained using ab initio methods.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030109
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  • 58
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    An algorithm for the generation of nuclear spin species and nuclear spin statistical weights (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 69-74 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article develops a set of algorithms for the computer generation of nuclear spin species and nuclear spin statistical weights potentially useful in molecular spectroscopy. These algorithms generate the nuclear spin species from group structures known as generalized character cycle indices (GCCIs). Thus the required input for these algorithms is just the set of all GCCIs for the symmetry group of the molecule which can be computed easily from the character table. The algorithms are executed and illustrated with examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030112
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  • 59
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    Electronic Resource
    The conformation of malformin A (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 89-94 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conformation of the cyclic pentapeptide malformin A has been deduced by systematically generating possible models for the molecule, and minimizing the conformation energy of each. Only one of the low-energy solutions is fully consistent with the reported CD and NMR spectra, and this is the proposed model. The disulfide ring linking adjacent cystine residues is highly strained, as has been predicted from the S—S vibration frequency. The conformation of the backbone, but not that of the disulfide ring, is similar to a model previously proposed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030114
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  • 60
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    Electronic Resource
    Graph theoretical classification and coding of chemical reactions with a linear mechanism (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 95-111 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Linear mechanisms of catalytic and noncatalytic chemical reactions which are theoretically feasible have been classified and coded using a detailed procedure for the unique numbering of cycles, edges, and vertices in the kinetic graphs. The following classification criteria are used in a hierarchical order: number of cycles and vertices, mutual connectivity of the cycles, manner of linking any pair of cycles, number of elements linking two cycles, mutual position of two cycles joined to a third one, orientation of edges, and presence of pendant vertices. All the types and classes of mechanisms are presented for reactions having up to five and four routes, respectively.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030115
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  • 61
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    Iterative calculation of eigenvalues and eigenvectors of large, real matrix systems with overlap (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 127-129 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An improved method for obtaining a few eigenvalues and eigenvectors of the symmetric matrix system is presented: \documentclass{article}\pagestyle{empty}\begin{document}$$(A - \lambda S)c = 0$$\end{document} where S ≠ I. The method allows us to handle larger systems more easily than any other known to the author. It requires the inversion of S, and N3 step, but thereafter each eigenvector and eigenvalue is obtained in a length of time proportional to N2. The relation of this method to the MOR and MMOR methods developed recently for handling the case, S = I, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030202
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  • 62
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    Koopmans' defects in metal group VIII carbonyls - a many-body approachPart 16 in the series: “Electronic Structure of Organometallic Compounds.” Part 15: M. C. Böhm and R. Gleiter, J. Organomet. Chem., to appear. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 140-153 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The ionization potentials of iron pentacarbonyl (1), ethylene-iron tetracarbonyl (2), cobalt tetracarbonylhydride (3), and nickel tetracarbonyl (4) have been calculated using a Green's function perturbation method based on the INDO approximation. It is shown that the deviations from Koopmans' theorem are largest in the Co complex, while the smallest reorganization energies of strongly localized MOs with predominant metal 3d character are found in the Fe carbonyls 1 and 2. The calculated Koopmans' defects are analyzed by an investigation of the relaxation terms of the self-energy part and are compared with previous INDO results for Cr, Mn, and Fe tricarbonyl derivatives. Additionally, orbital energies, bond indices, and net charges for the ground states of 1-4 are calculated and compared with experimental data.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/jcc.540030205
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    Theoretical studies on “acetylenic zipper” reaction intermediates (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 185-190 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Nonempirical molecular orbital studies on a series of isomeric octyn-1-ols indicated that the anomalous stability of the alkoxide of 3-octyn-1-ol isomer is probably related to stereochemical and polarization properties of the molecule. The calculations correlated with the experimental observation that the least stable isomer should be the terminal alkyne, 7-octyn-1-ol.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030209
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  • 64
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    Geometry and energy of overcrowded ethylenes. II. Bornanylidene, fenchylidene, and bifluorenylidene derivatives (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 178-184 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometry and energy of some bornanylidene, fenchylidene, and bifluorenylidene derivatives have been determined by the molecular mechanics method. Low twisting of the double bond was found for the compounds of the first two series. The difficulties found in the synthesis of 2-di-tert-butylmethylenefenchane can be related to a remarkable strain energy which is only slightly lower than that of tetra-tert-butylethylene. A twisted conformation is the preferred one in bifluorenylidene and its 1,1′-dimethyl derivative (E isomer) in agreement with experimental data. Conformational inversion and E-Z interconversion paths are discussed for the latter compound and theoretical results are compared with dynamic NMR data.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030208
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    Optimization of equilibrium geometries and transition structures (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 214-218 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A modified conjugate gradient algorithm for geometry optimization is outlined for use with ab initio MO methods. Since the computation time for analytical energy gradients is approximately the same as for the energy, the optimization algorithm evaluates and utilizes the gradients each time the energy is computed. The second derivative matrix, rather than its inverse, is updated employing the gradients. At each step, a one-dimensional minimization using a quartic polynomial is carried out, followed by an n-dimensional search using the second derivative matrix. By suitably controlling the number of negative eigenvalues of the second derivative matrix, the algorithm can also be used to locate transition structures. Representative timing data for optimizations of equilibrium geometries and transition structures are reported for ab initio SCF-MO calculations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030212
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    Studies in hydrogen bonding: Association within small clusters of water, methanol, and ammonia molecules using Jorgensen's intermolecular pair potentials (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 219-226 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometries of the dimer, trimer, and tetramer hydrogen-bonded clusters of water, methanol, and ammonia molecules have been derived using previously published intermolecular pair potentials containing constants optimized from ab initio calculations. The lowest energy forms for the dimers of all three types of molecules have an open structure, while the trimers and tetramers have cyclic structures. The results are compared with those previously described using another empirical potential, EPEN.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030213
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    The calculated structures of the C4H8NO+ cations resulting from the unimolecular gas-phase dissociation (CH3)2NCOCH2X·+ → C4H8NO+ + X· (X = CL, NO2) (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 251-259 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The structures and rearrangements of various cyclic and acyclic C4H8NO+ cations resulting from the title reaction have been investigated by means of semiempirical (MNDO) and ab initio (4-31G) calculations.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030217
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    Empirical penetration functions and two-center electron repulsion integrals for semiempirical calculations of electronic structure (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 265-268 
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    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Explicit functional forms for both the two-electron Coulomb integral, (aa∣bb), and the one-center core-orbital integrals, ZA-1 (aa∣ZA), are derived which permit the penetration integrals to be fully derived and calculated. With these forms the 3Σu+ of the H2 molecule is unstable. These forms are generalized so that they are suitable for optimizing semiempirical predictions of experimental one-electron properties.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030219
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    Announcement (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 274-274 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030223
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    Masthead (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982) 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030301
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    Calculation of macromolecular force constantsThis work was supported in part by NIH grant No. GM24443, NSF grant no. DMR-74-14367, and the American Cancer Society, grant No. IN17Q. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 297-304 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Force constant refinement may be carried under a system of constraints imposed on well characterized modes as the refinement proceeds. Resulting stability permits the accurate calculation of many independent macromolecular force constants. A useful formalism for this technique is developed. Prediction of initially poorly characterized modes can emerge from this stability. A brief discussion of currently used refinement schemes has been included. We show that the standard least-squares procedure is a special case of our present more general method, the former being useful when the molecule is not too large.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030304
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    Electronic Resource
    An ab initio study of the geometry, energy, and selected force constants for the three planar conformers of carbonic acid, and the bicarbonate ion; and of the energy for the reaction H2O + CO2 → H2CO3 (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 283-296 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio calculations using the unscaled 4-31G basis set have been carried out on the cc, tc, and tt conformers of carbonic acid and the bicarbonate ion, with full geometry optimization assuming the structures to be planar. The complete harmonic force field is reported for the (most stable) tt conformer and for the bicarbonate ion, also selected quadratic force constants for the cc and tc conformers. The changes in certain bond lengths and stretching force constants in the cc → tc, tc → tt, and cc → tt conformer conversion reactions are indicative of intramolecular hydrogen bonding, C=O…H—O and H—O…H—O, which is examined in greater detail by partitioning the overall conformer conversion energy into distortion and bonding energy components. The fundamental vibration frequencies for the tt conformer and the bicarbonate ion are calculated from the force constant matrices, and hence, using a scaling factor based on a comparison of calculated and experimental values for the bicarbonate ion and trans-formic acid, a value is predicted for the zero-point energy of the tt conformer. A new estimate of ΔH˚ for the hydration reaction, H2O + CO2 → H2CO3, at 298 K in the gas phase; is made from thermochemical data, +20.2 ± 3.4 kJ mol-1, which, together with estimates of (H298˚ - H0˚) and the zero-point energy for H2CO3, gives +8.1 ± 7.0 kJ mol-1 for ΔET(expt). ΔET calculated from the 4-31G basis set data is -29.1 kJ mol-1. Comparison of the experimental value, the Hartree-Fock limit value, and values calculated with a variety of basis sets for the bond separation reaction, CO2 + CH4 → 2H2CO, suggests that the differences, ΔET(expt) minus ΔET(SCF), are due mainly to basis set limitations and not substantial correlation energy contributions.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030303
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  • 73
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    Electronic Resource
    Structures of some fluorinated benzenes determined by ab initio computation (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 344-353 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The structures of fluorobenzene, 1,3-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,3-trifluorobenzene, pentafluorobenzene, and hexafluorobenzene have been determined by the ab initio gradient method with a 4-21 basis set. Approximate corrections have been developed to yield re and r0 structures so that comparison can be made with the available experimental information. The C—F bond distance decreases in a uniform manner with increasing fluorination of the ring, either on adjacent or on meta sites. The ring structure also shows systematic deformation, with a decrease of about 0.01 Å in the C—C bond length adjacent to the point of substitution and an increase of about 2.5˚ in the ring angle at the substitution site in those cases where the requirement of ring closure permits.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030309
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  • 74
    Electronic Resource
    Electronic Resource
    The conformation of pithomycolide (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 381-384 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conformation of the depsipeptide pithomycolide has been deduced by systematically generating possible models for the molecule, and minimizing their conformation energy. Only one of low-energy solutions is consistent with the reported NMR data.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030313
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  • 75
    Electronic Resource
    Electronic Resource
    Approaches to charge calculations in molecular mechanics (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 407-416 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Alternative methods of estimating atomic charges in haloalkanes are presented, derived from quantum mechanical and classical treatments. A scheme based on a breakdown of the transmission of charge by polar atoms into one-bond, two-bond, and three-bond additive contributions is given, in which the one-bond effect is proportional to the difference in the electronegativities of the bonded atoms, and the two- and three-bond effects functions of the atomic electronegativity and polarizability. Suitable developments of the basic scheme, including an iterative self-consistent process, give calculated dipole moments for a variety of haloalkanes in good agreement with the observed values. The atomic charges obtained by this scheme are compared with other estimates of these charges. They are similar to those derived from a simple LCAO-MO scheme but differ from those obtained by population analysis of more refined quantum mechanical calculations.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030316
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  • 76
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    Electronic Resource
    An improved method for the evaluation of transition states (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 277-282 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A simple but efficient coupled iteration procedure is proposed for searching saddle points and extrema along the line of constrained minimum energy paths by (analytical) calculation of the derivatives, i.e., the reduced forces and reduced force constants. The advantage of the method is shown with analytical potentials as well as a calculation of HCH—HNC rearrangement, as working examples.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030302
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  • 77
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    Electronic Resource
    Calculation of the average properties of atoms in molecules. II (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 317-328 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: This article describes an algorithm for the calculation of the average properties of an atom in a molecule. The atom is defined within the topological theory of molecular structure, a theory which defines atoms, bonds, structure, and structural stability in terms of the topological properties of a system's charge distribution. The average properties of the atom so defined are uniquely determined by quantum mechanics. Results for a number of hydrocarbon molecules, obtained by the program PROAIM (properties of atoms in molecules) which implements this algorithm, are given. In general, this program enables one to calculate the average energy of an atom in a molecule to an accuracy of ±1 kcal/mol.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030306
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  • 78
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    Electronic Resource
    Dynamics of ethyl radical decomposition. II. Applicability of classical mechanics to large-molecule unimolecular reaction dynamics (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 335-343 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The classical trajectory method is used to investigate the unimolecular dynamics of ethyl radical dissociation. It is found that chaotic trajectories need not be backward integrable to yield accurate lifetime, and product energy and angular momenta distributions. This allows the use of large numerical integration step sizes in trajectory calculations. The product energy and angular momenta distributions are independent of the ethyl radical lifetime, and are obtained after only 50 dissociation events. Differences between classical and quantal unimolecular dynamics are discussed, and a prognosis for future trajectory studies of large-molecule unimolecular decompositions is given.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030308
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  • 79
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    Electronic Resource
    Stabilization of methyl anions by first-row substituents. The superiority of diffuse function-augmented basis sets for anion calculations (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 363-371 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The entire set of methyl anions, XCH2-, substituted by first-row substituents, Li, BeH, BH2, CH3, NH2, OH, and F, was examined at various ab initio levels. Diffuse orbital-augmented basis sets, such as 4-31+G and 6-31+G*, are needed to describe the energies of these anions adequately. Estimates of proton affinities are further improved by second-order Møller-Plesset (MP2) electron correlation corrections, but relative energies are less affected. The methyl group in the ethyl anion is destabilizing, the amino substituent is borderline, but all other groups are stabilizing. Very large π effects are exhibited by BH2 and BeH groups; inductive stabilization by the electronegative F and OH groups is less effective. Lithium also is stabilizing, but the best singlet geometry of CH2Li- is not planar. A planar CH2Li- triplet with a π1 configuration may be lower in energy.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030311
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  • 80
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    Electronic Resource
    Spin-orbit and dispersion energy effects in XeF (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 372-380 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Spin-orbit and dispersion energy contributions to the energy curves of XeF are examined. A rapid variation in the spin-orbit coupling with internuclear separation is found for both the ground and excited states. This result can explain the experimentally observed ordering of the ionic excited states when the spin-orbit perturbation couples 2σ and 2π energy curves obtained by both all-electron and effective core potential (ECP) calculations at the first-order configuration interaction (FOCI) level of accuracy. Damped dispersion energy contributions to the ground-state energy curve are shown to be comparable to the charge transfer contribution. The energy curve for XeF is in reasonable agreement with experimental results and a calculation of the analogous XeCl curve confirms the qualitative correctness of the calculation. The energy curves and transition moments were then applied to two problems related to the efficiency of the XeF laser. Photodissociation of the X state provides a means of removing a bottlenecked vibrational level but a calculation of the radiative transition probability between the X and A states finds the cross section is too small to yield rates competitive with collisional deactivation. The bottlenecked state may also be removed by electron dissociative attachment but the calculated energy curves for the X states of XeF and XeF- do not cross at a low energy indicating a small cross section.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030312
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  • 81
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    Electronic Resource
    The 6-31G++ basis set: An economical basis set for correlated wavefunctions (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 561-564 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The 6-31G++ basis set is described. This basis set is very similar to the existing 6-31G** set but is somewhat smaller through the use of five (rather than six) second-order Gaussians (d functions) and has polarization function exponents optimized for correlated rather than Hartree-Fock wavefunctions. The performance of 6-31G++ is compared with that of the 6-31G** and 6-31G** basis sets through calculation of the geometries and atomization energies for the set of molecules LiH, FH, H2O, NH3, CH4, N2, CO, HCN, and HCCH.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030414
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  • 82
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    Electronic Resource
    Conformation analysis of small molecules with PCILO methods (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 580-587 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conformational potential of n-butane, ethyl methyl ether, n-propanol, methyl propyl ether, and 1,2-dimethoxyethane was calculated with different PCILO algorithms as well as with ab-initio SCF-LCAO-MO computations. Compared with ab-initio calculations, the conformational potentials obtained by PCILO methods on the same geometries are too flat. In particular, the barrier at 0˚ (synperiplanar conformation) is much too low at the second- and third-order level. This is mainly a consequence of the second-order delocalization corrections. Since the PCILO algorithms are not capable of reproducing conformational potentials obtained from ab-initio calculations, only qualitative predictions are possible.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030417
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    Computational chemistry, An introduction to numerical analysis, A. C. Norris, Wiley, New York, 1981, 454 pp. Price: $46.95. (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 604-604 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030421
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    Electronic Resource
    Announcements (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 605-605 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540030422
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