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  • 1985-1989  (469)
  • 1920-1924
  • 1988  (469)
  • Computational Chemistry and Molecular Modeling  (332)
  • Physical Chemistry  (137)
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Years
  • 1985-1989  (469)
  • 1920-1924
Year
  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 115-117 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A novel oxygen induced reduction of α,β-unsaturated carbonyl compounds is discovered. The reduction of the carbon-carbon double bond of α,β-unsaturated carbonyl compounds by benzeneselenol was caused by an introduction of molecular oxygen into the reaction system. This reduction is likely to proceed via a radical chain pathway involving an SH2 type reaction between a phenylseleno radical and a 1,2-adduct of benzeneselenol to the carbonyl group of the α,β-unsaturated carbonyl compound to give an allylic radical which absracts a hydrogen atom from benzeneselenol to form the reduction product.
    Additional Material: 1 Tab.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 191-195 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photochemical reaction of MAQO with various aromatic amines were studied by ESR. The results show that nitroxide radicals are stable productrs of the photooxidation of both diphenylamines and phenylamines. The photolyzed phenothiazine does not yield nitroxide as the final product, instead it gives the neutral radical as the stable final product.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 333-349 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New series of platinum complexes of cyclopropenylidenes of the types of PtX2(CP)2 and trans-PtX(PBu3)2(CP) have been synthesized, where CP is di-t-butylcyclopropenylidene (BCP) or bis(diisopropylamino)cyclopropenylidene (ACP). The 13C-NMR chemical shifts, and 13C-195Pt coupling constants (1JPtC) for the complexes are discussed in comparison with those values derived from closely related series of compounds, trans-PtCl(PR3)2L; L — —CH3, —C6H5 and —C≡CBu-t. An excellent linear relationship through the origin was obtained between 1JPtC and the formal ‘s’ % character of the carbon directly bonded to Pt for the series trans-PtCl(PR3)2L in which the Pt—C bond is regarded as a pure σ-linkage, whereas 1JPtC deviates largely from this relationship when pπ—dπ bonding interaction possibly exists in the Pt—C bond. The NMR data suggest the strong nmr trans-influence of the cyclopropenylidenes and that in the Pt—CP bond the σ-interaction is appreciable but the π-interaction is negligible.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 123-131 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of N-alkyl-N-(3-aryl-3-butenyl) ureas (1) in acetonitrile gave cyclization products, 3-aryl-3-methyl-pyrrolidines, in good yields, whereas irradiation of 1 in methanol afforded methanol adducts as well as the cyclization products. Both the reactions are singlet reactions, and the cyclization is presumed to proceed via 1,6-hydrogen transfer from exciplexes with charge transfer character.
    Additional Material: 2 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 143-151 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dependence of the catalytic efficiencies of sodium carboxymethylamylose (NaCMA) for the hydrolysis of N-lauryl-3-acetoxypyridinium iodide (1) and p-nitrophenyl dodecanoate (3) on its degree of substitution (D. S. = 0·00, 0·12, 0·18, 0·24, 0·29 and 0·35) and on the pH values of the solutions (pH = 7·32, 7·80, 8·10 and 9·30) have been studied. At fixed D. S. values, the observed hydrolysis rates of 1 and 3 increase with increasing concentrations of NaCMA and follow saturation kinetics. At fixed concentration of NaCMA, the rates increase with decreasing D. S. values until they reach maxima at D. S. = 0·00. Furthermore, at any D. S. value the catalytic efficiency increases with increasing pH values of the solutions. All these results indicate that the hydroxyl groups are actually the principal catalyzing groups.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 169-178 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The development of positive charge β to silicon in a saturated five-membered ring has been studied in the cis- and trans-2-(trimethylsilyl)cyclopentyl trifluoroacetates. The cis substrate solvolyzes in 97% trifluoroethanol at 25° C about 5 times faster than the analogous six-membered ring, after correction for differences in ring strain. The trans substrate solvolyzes about 360 times more slowly than the analogous six-membered ring. These changes are in agreement with a hyperconjugative mechanism for interaction between the silyl group and the developing positive charge. The expected cosine-squared dependence of hyperconjugation on the Si—C—C—X dihedral angle suggests that the cis dihedral angle is reduced somewhat from the 60° in the six-membered ring, and the trans dihedral angle is reduced substantially from the 180° in the six-membered ring.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 209-223 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The equilibrium acidities of phenylacetonitrile, and 20 of its m- and p-substituted derivatives have been measured in Me2SO solution. Their pKa′s plot linearly with those of the corresponding anilines. Combination of the pKa′s of these acids with their oxidation potentials, Eox(HA), and those of their conjugate bases, Eox(A-), provide an estimate of the acidities of the corresponding radical cations. The pKHA+ values for ArCH2CN+., where Ar is Ph, 1- and 2-naphthyl, and 9-anthryl, are -32, -18·5, -17·5, and -11, respectively, compared to 21·9, 20·85, 20·65, and 19·8 for the corresponding ArCH2CN acids. Acidities of PhCH(Me)CN+., Ph2CHCN+., 9-CN-FlH+., and 9-CN-XnH+. are -33, -35, -25, and -27, respectively, compared to 23·0, 17·5, 8·3, and 13·6 for the corresponding acids from which they were derived. The homolytic bond dissociation energies (BDEs) for the benzylic C—H bonds in these arylacetonitriles, estimated by combining pKHA with Eox(A-), fall in the range of 69 kcal/mol for 9-CN-XnH to 82 kcal/mol for PhCH2CN. For GC6H4CH2CN+. radical cations the acidities are decreased, relative to G=H, when G is an electron donor substituent and increased when G is an acceptor. The BDEs of the benzylic C—H bonds in GC6H4CH2CN are weakened by up to 4 kcal/mol by para donors and strengthened by up to 1·2 kcal/mol by m- or p-acceptors. The significance of these changes in BDEs with regard to the use of σ. scales and the ΔAOP method for estimating substituent effects on radical stabilities is discussed.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 259-265 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1-(Phenylazo)-1-(2-pyridyl)ethyl hydroperoxide, 1, 1-(phenylazo)-1-(2-furyl)ethyl hydroperoxide, 2, phenylazo(2-furyl)methyl hydroperoxide, 3, 1-(phenylazo)-1-(4-anisyl)ethyl hydroperoxide, 4, were synthesized in moderate yield by autoxidation of the phenylhydrazones in benzene. The ionic oxidation of benzyl methyl sulfide in benzene by 1-4 yielded the sulfoxide and the metastable α-azo hydroxides in essentially quantitative yield. The reaction was of the first order in α-azo hydroperoxide and sulfide, respectively. The relative reactivity series found was: 1(1.0) 〈4(1.4) 〈 phenylazo(4-anisyl)methyl hydroperoxide 5 (2·9) 〈2 (3·8) 〈 3 (9·6). α-Methyl substitution was found to slow the rate of oxygen-atom trasfer by a factor of 2 to 2.5. The low relative reactivity of 1 was opposite that expected based on electronic effects. Competitive intramolecular hydrogen bonding of the hydroperoxy proton to the pyridyl nitrogen in 1 accounted for the observed result.
    Additional Material: 2 Tab.
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  • 11
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 281-285 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal and photochemical decompositions of 5 have been studied. Both reactions lead to CBr2 transfer in good to high yields. With the 2-pentenes as substrates, CBr2 transfer is stereospecific in the classical singlet carbene manner.
    Additional Material: 3 Tab.
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  • 12
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 305-308 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Decomposition of the tosylhydrazone salts formed from cubyl carboxaldehyde and homocubanone, potential precursors of cubylcarbene (5) and homocubanylidene (6), leads in each case to products derived from 6. It is suggested that homocub-1(9)-ene (7) is the active ingredient in the formation of 6 from both precursors. The hydrazones formed from N-aziridylamines are useful photochemical sources of 6, and presumably other carbenes. Flash vacuum pyrolysis of the tosyl hydrazone salts and hydrazones at 600°C leads to indene.
    Additional Material: 1 Tab.
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  • 13
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 317-332 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Light- and heat-induced decompositions and reactions with nucleophiles of 6,6,8,8-tetramethyl-2-selena-3,4-diaza-7-oxabicyclo[3.3.0]octa- 1(5),3-diene have been studied. In contrast with the conversion to the cyclopentyne derivative (9), selenium containing intermediates (6a, 6b, and 7) were efficiently trapped using several reagents to give various kinds of organoselenium compounds. Of particular note is the isolation of a stable selenirane derivative (16) obtained by the cycloaddition of the photochemically generated selenirene intermediate (7) with furan. The character and reactivity of the intermediates are also discussed.
    Additional Material: 3 Tab.
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  • 14
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 359-362 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction rates for solvolysis of a mustard analogue are accurately correlated by the solvatochromic equation without inclusion of a nucleophilicity term, and thus the equation is shown to reveal mechanistically significant information.
    Additional Material: 1 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 247-257 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate of hydrolysis of the aromatic vinyl ether o-carboxy-α-methoxy-β,β-dimethylstyrene was found to be accelerated 25-fold by ionization of its carboxylic acid group, but the effective molarity which may be calculated if all of this rate acceleration is ascribed to intramolecular general acid catalysis is only EM = 1 · 1 m. This is similar to the small effective molarities found before for intramolecular catalysis by carboxylic acid groups of aliphatic vinyl ethers, which shows that, unlike the situation in other intramolecular reactions, e.g. ketone enolization, the extra rigidity of aromatic over aliphatic systems does not improve the efficiency of intramolecular catalysis in vinyl ether hydrolysis.It is suggested that this behaviour is the result of reduced conjugation between the vinyl ether group and the aromatic ring in the transition state of the vinyl ether hydrolysis reaction, which retards the rate and offsets any improvement effected by increased rigidity of the aromatic system.
    Additional Material: 2 Ill.
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  • 17
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2,2′-Diselenocyanato-1,1′-binaphthyl(1), the first selenium-containing binaphthyl derivative, has been synthesized in optically active form the corresponding diamine by diazotization followed by the reaction with potassium selenocyanate. Its molecular structure is determined by X-ray diffraction method. It is revealed that selenium atoms have hypervalent penta-coordination in the crystal.
    Additional Material: 4 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 287-298 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio STO-3G and 6-31G minimized geometries of 5-oxo- (9), 6-oxo-7-oxabicyclo[2.2.1]hept-2-yl cation (12) and 7-oxabicyclo[2.2.1]hept-2-yl cation (15) were obtained. The energy barriers for their Wagner-Meerwein rearrangements to the more stable 5-oxo- (11), 6-oxo-3-oxabicyclo[2.2.1]hept-2-yl (13) and 3-oxabicyclo[2.2.1]hept-2-yl (17) cations, respectively, have been evaluated and compared with those calculated for the rearrangement of the 5-oxo (18) and 6-oxobicyclo[2.2.1]hept-2-yl cations (20). In agreement with experimental data, the ‘true migratory aptitude’ of an acyl group is higher than that of β-oxoalkyl group in competitive Wagner-Meerwein rearrangments that are ‘energetically unbiased’. The ease of the acyl group 1,2-shift toward an electron-deficient center is related to the electron-donating ability of the carbonyl group due to favorable n(CO) ↔ σ σ ↔ p(C+) hyperconjugative interaction.
    Additional Material: 1 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 299-303 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Iodide ion promotes the free radical reaction of isopropylmercury idide with bromotrichloromethane to yield isopropyl bromide with rate enhancement in the order of 104. The reaction involves electron transfer from i-PrHgI2- to the trichloromethyl radical in a long kinetic chain process. Iodide ion also promotes the free radical chain conjugate addition of tert-butylmercury chloride to α,β-unsaturated ketones, esters, phosphonate esters and sulfones. Competitive reactivity studies indicate that lithium di-tert-butylcuprates or tri-tert-butylzincates react with 2-cycloalkenones by a mechanism involving attack by tert-butyl radicals. No evidence for radical attack is observed for the corresponding n-butyl ate complexes of copper or zinc.
    Additional Material: 1 Tab.
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  • 20
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 103-114 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of solvent additives on the course of TiO2 photocatalyzed oxygenation of α-methylstyrene has been studied. While the addition of small amounts of nonhalogenated alcohols to TiO2 powders suspended in acetonitrile was found to decrease the rate of photooxygenation, added halogenated alcohols increase the rate of reaction. In addition, the solvent additives affect the observed product distribution.
    Additional Material: 4 Tab.
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  • 21
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 119-121 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reduction of aromatic aldehydes by benzeneselenol is found to be promoted by molecular oxygen to give corresponding alcohols in good yields. No reduction took place without oxygen.A free radical process involving SH2 reaction at the selenium atom is proposed where the phenylseleno radical attacks the selenium atom of selenohemiacetal, the adduct of benzeneselenol to aldehyde, to give the ketyl radical which then abstracts hydrogen from benzeneselenol. The intermediacy of selenohemiacetal is supported by a quantitative reduction of α-methoxybenzyl phenyl selenide, which is used as a model compound of the intermediate.
    Additional Material: 1 Tab.
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  • 22
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dependency of the wrapping-up capability of sodium carboxymethylamylose (NaCMA) on its degree of substitution (D. S. = 0·00, 0·12, 0·18, 0·24, 0·29, 0·35 and 0·41) have been studied, using two guest species, iodine and cetyl-trimethylammonium bromide (CTAB). The λmax values of NaCMA-iodine helical inclusion complexes decrease with increasing D. S. values and the amounts of encapsulated iodine by NaCMA as measured by amperometric titrations also decrease with increasing D. S. values. With CTAB as the substrate, the largest number of binding sites, n, and the dissociation constants Kd have been determined by the method of surface tension versus the CTAB concentration plots. The results show that n decreases while Kd increases with increasing D. S. values. All these observations point to the fact that the wrapping-up capability of NaCMA decreases with increasing degrees of substitution. The results are discussed in terms of host-guest and host-solvent hydrophobic-lipophilic interactions as well as intramolecular hydrogen-bonding.
    Additional Material: 6 Ill.
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  • 23
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 161-167 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature-dependence of the kinetic isotope effects for branched reactions proceeding via a common intermediate has been simulated by calculations. It is shown that, under certain conditions, anomalously small isotope effects on the Arrhenius preexponential factors, as well as unusually large observed isotope effects, may originate from the branching.
    Additional Material: 2 Ill.
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  • 24
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 153-160 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of the allyl anion (1) and two fluoro-substituted derivatives, perfluoro (2) and 1,1-difluoro (3) have been calculated by ab inito molecular orbital theory. Geometries were gradient optimized, and force fields and an MP-2 correlation correction were determined at stationary points. The calculations were done with a double zeta basis set augmented by d functions on carbon (DZ + Dc). Final self-consistent field (SCF) and MP-2 energy calculations were done with the DZ + Dc basis set augmented by diffuse functions. The ground state of 1 is the planar allyl anion (C2v). The rotation barrier in 1 is 21·1 kcal/mol at the MP-2 level. The cyclopropyl carbanion is 27·0 kcal/mol higher in energy at the MP-2 level. The perfluoroallyl anion is not planar, and the rotated structure is 25·7 kcal/mol more stable than the C2v structure at the MP-2 level. The lowest energy structure on the potential energy surface for 2 is the perfluorocyclopropyl carbanion which is 27·8 kcal/mol more stable than the C2v structure at the MP-2 level. The 1,1-difluoroallyl anion is also not planar. Here the most stable structure on the potential energy surface is the rotated allyl anion which is 8·3 kcal/mol more stable than the all-planar allyl anion structure.
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  • 25
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 241-245 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of solvolysis of l-aryl-l-phenyl-2,2-dimethylpropyl(1) p-nitrobenzoates and of aryldiphenylmethyl-p-nitrobenzoates (2) were measured in 80% acetone. An inverse order of reactivity, kp-CF3/km- CF3 〉 l was observed for 1 but not for 2. The X-ray crystallogoraphic study of the parent compounds, l,l-diphenyl-2,2-dimethylpropyl-p-nitrobenzoate (1b) and triphenylemethyl benzoate (3b), and of 2-phenyl-2-propyl-p-nitrobenzoate (4) indicated that in the highly congested system 1 both phenyl rings were nonplanar, whereas the phenyl rings in 3 and 4 were essentially planar.
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  • 26
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 185-190 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: From the 1H-NMR spectra of the various pyrrole compounds, 1-substituted 2,5-dimethylpyrroles having two substituent groups on the carbon adjacent to the nitrogen atom were found to be very much hindered compounds. 1-[(1-Substituted)-2-phenylethyl]-2,5-dimethylpyrroles showed the restricted rotation, and the phenyl group of the most stable conformer was in close proximity to the pyrrole group due to dipole interaction. These NMR observations were supported by force field conformational analysis.
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  • 27
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988), S. 197-207 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: ESR spectra of l-cyano-2-(trimethylsilyl)ethyl and related radicals were recorded. Temperature dependent ESR spectra of these radicals revealed that electron-releasing trimethylsilylmethyl and electron-withdrawing cyano groups synergetically functioned to stabilize the radical centers due to σ-π captodative effects.
    Additional Material: 10 Ill.
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  • 28
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The excellent linearity (R2 = 0·997) of a plot of pKa values for 17 m- and p-substituted benzyl phenyl sulfones, GC6H4CH2SO2Ph, vs. those for the corresponding arylacetonitrile, GC6H4CH2CN, demonstrates that substituent solvation and substituent solvation assisted resonance (SSAR) effects for p-CN, p-COPh, and p-SPh are nearly identical in these two substrates. The PhSO2 group in PhCH2SO2Ph increases the BDE of the α-C—H bond by 2 kcal/mol, relative to toluene. The α-C—H bonds in GC6H4CH2SO2Ph sulfones are stabilized by 1-2 kcal/mol by acceptor G′s (m-CN, p-CN, m-CF3, p-CF3), but weakened by 1 and 5 kcal/mol, respectively, by donors (p-OMe and p-NMe2). The GC6H4CH2SO2Ph+. radical cation with G = H has a pKHA+. = -25. Its acidity is increased when G is an acceptor by as much as 9 to 10 kcal/mol (G = 3-CN, 3-CF3, 4-CF3, 4-NO2), but is decreased when G is a donor by as much as 33 kcal/mol (G = NMe2). When G = 4-SPh the radical cation is stabilized, relative to G = H, by a larger amount (25 kcal/mol) than when G = 4-OMe (18 kcal/mol). Structural changes along the series PhCH2SO2Ph, 2-naphthyl-CH2SO2Ph, 9-anthryl CH2SO2Ph cause negligible changes in the acidities of these acids, but sizable decreases in the acidities of the corresponding radical cations. Introduction of a phenylsulfonyl group into the methyl group of 9-methylanthracene or the 9-position of fluorene or xanthene increase the BDEs by 3, 2, and 7 kcal/mol, respectively. These effects of PhSO2 groups are compared and contrasted with those of CN groups.
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  • 29
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    Journal of Physical Organic Chemistry 1 (1988), S. 267-273 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The PE spectra of four stable bicyclic triaziridines with trifluoromethyl, methyl, phenyl, spirocyclopentane and spirocyclohexane substituents are measured. From a comparison of these experimental data with MNDO calculations the energies and the interactions of the nitrogen lone-pair orbitals were obtained. The trifluoromethyl group may be reliably simulated by a fluorine atom. The ionization potentials are unexpectedly high and so are the cyclovoltammetric anodic potentials. The MNDO valence electron densities are in agreement with the comparatively small differences in the chemical shifts of the differently substituted nitrogens of the triaziridine rings.
    Additional Material: 2 Ill.
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  • 30
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    Journal of Physical Organic Chemistry 1 (1988), S. 275-280 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In order to examine the substituent effect of ethylenedithio and trimethylenedithio groups on electron acceptors, the two title compounds were prepared in one step from the corresponding quinones. These species behave as weak π-electron acceptors owing to the electronic and sterical effects of the fused groups. Only the bis(ethylenedithio) derivative formed a charge-transfer complex with tetrathiotetracene, which showed a moderate electric conductivity of 2·0 × 10-2 S cm-1. In addition, both species oxidized copper, sodium, and potassium iodides to give the corresponding deeply colored metal salts, most of which were semiconductive. The naphtho analogs were similarly studied, but hardly served as electron acceptors.
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  • 31
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 32
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photoresponse of the poly(vinyl chloride) membranes, which contain spirobenzopyran and crown ether, covered with a urease layer was studied in the presence and absence of urea. In the absence of urea, UV light irradiation induced more than 160 mV of membrane potential change, whereas the photoresponse decreased with an increase in the concentration of urea in the solution. The effects of such operating variables as crown loading and pH and ionic strength in the aqueous phase on the potentiometric response were also elucidated in the presence of urea. The results were explicated using the fact that the local concentration on NH4+ and H+ ions changed as a result of the urease-catalyzed decomposition reaction of urea.
    Additional Material: 8 Ill.
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  • 33
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    Journal of Physical Organic Chemistry 1 (1988), S. 351-357 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The title reaction is an instance of a simple nucleophilic attack of neutral nitrogen on aromatic sp2 carbon. The kinetic data (obtained in dimethyl sulphoxide) are compared to the results reported by the literature for the same reaction of aliphatic amines. Some possible interactions (substrate/nucleophile, substrate/salt) preceding the attack of the nucleophile are discussed.
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  • 34
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    Journal of Physical Organic Chemistry 1 (1988), S. 21-27 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structure of radical intermediates appearing in the reactions of MeMgBr with aromatic monoketones was investigated by using ESR and visible spectroscopy. Stable radical intermediates in the reacting solutions were assigned to the dimeric radical ion pairs.
    Additional Material: 3 Ill.
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  • 35
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    Journal of Physical Organic Chemistry 1 (1988), S. 33-38 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Several Cotton effects are developed within absorption bands of trinuclear organotransitionmetal complexes in the presence of acids, diols, amines and aminoalcohols even in the case of bulky substituents on nitrogen; with monohydroxy compounds no circular dichroism could be detected.
    Additional Material: 4 Ill.
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  • 36
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    Journal of Physical Organic Chemistry 1 (1988), S. 29-31 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Disparity reaction proposed in a recent application of Marcus-Grunwald theory to nitroalkane ionization is shown to put the reaction's transition state in an energy-diagram region where electronic rearrangement leads proton transfer, contrary to experimental evidence; it is suggested that addition of solvent reorganization to electronic rearrangement as the second reaction progress variable would remedy this situation.
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  • 37
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    Journal of Physical Organic Chemistry 1 (1988), S. 39-46 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Triethylsilyl radical was generated by laser flash photolysis of a 1:1 (v/v) solution of triethylsilane and di-tert-butyl peroxide. The silicon centered radical was reacted with sulfides to give carbon centered radicals by displacement at sulfur. The carbon radicals were readily detected by their transient absorption spectra. The absolute rate of reaction of triethylsilyl radical with 9-fluorenylphenylsulfide, di-n-butylsulfide, di-sec-butyl sulfide, di-tert-butyl sulfide and di-n-butyl disulfide are 2.40 ± 0.12 × 108 M-1S-1, 1.1 × 107±0.89×106M-1S-1, 8.79± 0.73×106M-1S-1, 3.29±0.18×106 M-1S-1, and 3.41±0.09×108 M-1S-1, respectively.
    Additional Material: 8 Ill.
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  • 38
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    Journal of Physical Organic Chemistry 1 (1988), S. ii 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 39
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 1 (1988) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 40
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    Journal of Physical Organic Chemistry 1 (1988), S. 1-20 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Substrates with neutral leaving groups undergo unimolecular solvolysis in nonpolar solvents. Whereas t-alkyl substrates invariably solvolyze by a unimolecular mechanism, s-alkyl and primary alkyl substrates can undergo both uni and bimolecular reactions, and the bimolecular step can take place on either the substrate itself or on an intimate ion-molecule pair formed in either a pre-equilibrium or in a rate determining step. Study of reactions at borderlines indicates that the individual reaction types remain distinct and do not merge.
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  • 41
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    Journal of Physical Organic Chemistry 1 (1988), S. 59-61 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Treatment of α, α′ -diketo selenides, which recently became readily obtainable, with base affords α-oxo selenoaldehydes and ketones. The seleno-carbonyl compounds thus formed are reactive transient species, but can be trapped by Diels-Alder reaction to give 3,6-dihydro-2H-selenapyran derivatives in moderate to good yields.
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  • 42
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    Journal of Physical Organic Chemistry 1 (1988), S. 47-51 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This paper describes the synthesis and electrochemical behavior of dicationic salts of ethenediylidene-2,2′ -bis(1,3-dithiole) (3) and butatriene-1,4-diylidene-2,2′ -bis(1,3-dithiole) (4). These are expected as donor components for developing organic conducting and superconducting materials, on the grounds of high electron donating ability and of rigid skeletal structure with two and four cumulenic carbons inserted between two 1,3-dithioles. These salts were obtained in good overall yields by several steps starting from (2-morpholino-4,5-dimethyl or -diphenyl)-1,3-dithiolylium salt. From the 1H and 13C NMR, and electronic spectra it is suggested that the π conjugation between two 1,3-dithiolylium ions through an acetylenic bond is less effective than that through an olefinic bond of the corresponding salts of ethanediylidene-2,2′ -bis(1,3-dithiole) (1) and 2-butene-1,4-diylidene-2,2′-bis(1,3-dithiole) (2). The cyclic voltammetric study shows that the corresponding radical cations, and in particular 3 and 4, are less stable even at -40°C, thus providing reasons for our current lack of success in isolation of 3 and 4. From comparison of the first redox potentials of neutral species, it is deduced that the donating ability increases in the order of TTF 〈 1 ⋍ 2 ≲ 3 ≪ 4.
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  • 43
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    Journal of Physical Organic Chemistry 1 (1988), S. 53-57 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of sulfur ylides with elemental sulfur or selenium initially affords thio- or seleno-carbonyl compounds, which then react with starting ylides to give episulfides or episelenides from which the heteroatom (sulfur or selenium) is extruded to give olefins as the final product. In the case of carbonyl-stabilized ylides, the resulting thio- or seleno-carbonyl compounds react with starting ylides to afford 1,3-oxathioles or 1,3-oxaselenoles as previously reported. Supporting evidence for the intermediacy of thio(seleno)-carbonyl compounds and episulfides (episelenides) is presented.
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  • 44
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    Journal of Physical Organic Chemistry 1 (1988) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 45
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    Journal of Physical Organic Chemistry 1 (1988), S. 63-73 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Novel structural features of 5, 15-dialkylporphyrins in solution are described. The 1H-NMR spectra of these compounds showed broad signals at room temperature, which split into two sets of signals at lower temperatures. This unusual phenomenon was ascribed to a dynamic interconversion between tow distorted structures. The 5, 15-dialkylporphyrin has a distorted ring due to the steric hindrance between the 5(or 15)-alkyl group and the 3, 7(or 13, 17)-alkyl groups and, depending on the position of the 5, 15-alkyl groups relative to the average ring plane, can exist in two conformations; syn (where the two alkyl groups are on the same side of the ring plane) and anti (on the opposite sides). Preliminary kinetic study of this interconversion using the NMR line shape analyses is also reported.
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  • 46
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    Journal of Physical Organic Chemistry 1 (1988), S. 75-81 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Highly sterically demanding 2,4,6-tri-t-butylphenyllithium (1) reacts with carbon disulfide to give 1,2-dibutylthio-1,2-bis(2,4,6-tri-t-butylphenylthio) ethene (3), l-butylthio-1-(2,4,6-tri-t-butylphenylthio)pent-l-ene (4), and 2-butylthio-3-(2,4,6-tri-t-butylphenylthio)-1,3-dithiole-2-thione (5) when 1 is prepared by the reaction of 1-bromo-2,4,6-tri-t-butylbenzene with n-butyllithium. When the reaction is carried out using 1 prepared from 2 and t-butyllithium and then quenched with l-iodoethane, 2-ethylthio-3-(2,4,6-tri-butylphenylthio)-1,3-dithiole-2-thione and 1,2-diethylthio-1,2-bis(2,4,6-tri-t-butylphenylthio) ethene are produced. The formation of all these products can be explained in terms of initial thiophilic attack of 1 on the sulfur of carbon disulfide and an intermediate with a dual property of carbanion and carbene (i.e., ArSC(Li)(=S) ⇌ ArSC̈SLi) is suggested. The reaction of 1 with thiophosgene affords 1,2-dichloro-1,2-bis(2,4,6-tri-t-butylphenylthio) ethene, bis(2,4,6-tri-t-butylphenylthio)acetylene, and 1-chloro 2,4,6-tri-t-butylbenzene, the first two of which are explained to be formed by thiophilic attack of 1 with thiophosgene.
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  • 47
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    Journal of Physical Organic Chemistry 1 (1988), S. 91-102 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photolysis of benzoinalkylethers 1-5 solubilized in detergents show a significant deviation from the course of reaction in isotropic organic solvents. Remarkable difference in photobehaviour is noticed between the short chain (1-3) and the long chain (4 and 5) benzoinalkylethers in the micellar media. However, the influence of the micellar media on the photobehaviour of alkyldeoxybenzoins 6 and 7 was small. The importance of ‘cage effect’ in controlling the product distribution was evident from its dependence on the micellar size and on the occupancy number. More importantly, a comparative analysis of the photobehaviour of the ketone 1-7 reveals that the micellar interface can be used to control the conformations of organic molecules.
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  • 48
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    Journal of Physical Organic Chemistry 1 (1988), S. 83-90 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Theoretical studies on the reactions of ammonia with ketene and dimethylketene using the MNDO method are reported. The single step addition of ammonia to the olefinic bond of ketenes was found to provide a lower energy-barrier path than the two step carbonyl addition mechanism. The barrier height was lower in the reaction of keten compared with that of dimethylketene in support of the faster rate of solution phase reactions of aniline and ketenes. The deformation energies of reactants had an overwhelming influence in determining the activation barriers in all the reactions investigated.
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  • 49
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    International Journal of Quantum Chemistry 33 (1988) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 50
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    International Journal of Quantum Chemistry 33 (1988), S. 19-26 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A completely analytic method for evaluating three-center nuclear attraction integrals for STOS is presented. The method exploits a separation of the STO into an ‘evenly loaded’ solid harmonic and a OS STO. The harmonics are translated to the molecular center of mass in closed finite terms. The OS STO is translated using the Gegenbauer addition theorem; 1s STOS are translated using a single parametric differentiation of the OS formula. Explicit formulas for the integrals are presented for arbitrarily located atoms. A numerical example is given to illustrate the method.
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  • 51
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    International Journal of Quantum Chemistry 33 (1988) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 52
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    International Journal of Quantum Chemistry 33 (1988), S. 87-113 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two three-dimensional numerical schemes are presented for molecular integrands such as matrix alements of one-electron operators occuring in the Fock operator and expectation values of one-electron operators describing molecular properties. The schemes are based on a judicious partitioning of space so that product-Gauss integration rules can be used in each region. Convergence with the number of integration points is such that very high accuracy (8-10 digits) may be obtained with obtained with a modest number of points. The use of point group symmetry to reduce the required number of points is discussed. Examples are given for overlap, nuclear potential, and electric field gradient integrals.
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  • 53
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new definition of a canonical set of bonded functions has been introduced. For a given configuration with r singly occupied orbitals and given multiplicity, the set exhibits symmetry properties of a group of order r. It simplifies the evaluation of the energy matrix H as well as the orthogonalization procedure.
    Additional Material: 2 Ill.
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  • 54
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    International Journal of Quantum Chemistry 33 (1988), S. 369-369 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 55
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    International Journal of Quantum Chemistry 33 (1988) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 56
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    International Journal of Quantum Chemistry 33 (1988), S. 373-394 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine various perturbation-variational approximations for molecular electronic energy when the fifth-order perturbational energies are available. Such theories require very little additional computation once the sequence of perturbation energies are known yet supply a bound even when the peturbation sequence is poorly convergent. We choose for computational examples results obtained very rapidly from a zeroth order wave function consisting of doubly occupied localized bonds and examine polarization within these bonds, delocalization, and bond breaking. In general, we find that the fifth-order energy itself, and especially the [2, 1] Padé approximant on this sequence, are especially accurate in estimating the total energy and more accurate than any variational scheme when the zeroth order localized wave function is a good description of the electronic structure. The variational results, however, are nearly as accurate, and a [1, 0] Padé on the sequence of variational results is remarkably robust, even in those cases where the perturbation sequence is poorly defined.We also examine several scaling techniques, or partitionings of the Hamiltonian. Although these scaling techniques do accelerate convergence of the perturbation sequence, none that we examine give better results, than the [2, 1] padé, which is independent of any scaling.
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  • 57
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    International Journal of Quantum Chemistry 33 (1988) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 58
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    International Journal of Quantum Chemistry 34 (1988), S. 1-8 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new MO-LCAO description of the nephelauxetic effect is proposed based on the concept of the topological atom and on the method of reduced density matrices. This approach allows one to overcome some conceptual difficulties of ligand-field theory and to derive effective parameters of d-d electron repulsion of a bound transition-metal in a proper way. The two ligand-field mechanisms of the nephelauxetic effect - the central field covalency and the symmetry-restricted covalency - are clarified and generalized. In addition, a new factor, important for the nephelauxetic effect is found: its size-dependence on the region of the topological atom.
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  • 59
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    International Journal of Quantum Chemistry 34 (1988), S. 47-71 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Hartree-Fock (HF) self-consistent field (SCF) crystal orbital (CO) formalism for two- and three-dimensional (2D/3D) solids on the basis of semiempirical CNDO/INDO (complete neglect of differential overlap; intermediate neglect of differential overlap) Hamiltonians is presented. The employed SCF variants allow for the treatment of atomic species up to bromine under the inclusion of the first (i.e., 3d) transition metal series. Band structure investigations of 2D and 3D materials containing more than 30 atoms per unit cell are feasible by the present SCF HF CO formalism. The theoretical background of the computational scheme is given in this contribution. Special emphasis is placed on physically reliable truncation criteria for the lattice sums, the adaptation of the crystal symmetry in k space, as well as the suitable choice of domains in Brillouin zone (BZ) integrations required in the determination of charge-density matrices. The capability and limitations of the semiempirical SCF HF CO approach is demonstrated for some simpler solids by comparing the present computational results with those of ab initio CO schemes as well as conventional numerical methods in soid-state theory. The employed model solids are graphite and BN (2D and 3D networks for both solids) as well as diamond, silicon, germanium, and TiS2.
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  • 60
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    International Journal of Quantum Chemistry 34 (1988), S. 143-160 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamics of a model triatomic hydrogen bond are analyzed through classical mechanics. The approximate separability of the equations of motion induces the existence of an adiabatic invariant for the intramolecular mode motion. This mode is governed by a Mathieu equation, a feature already present for the antisymmetric mode in symmetric triatomics. The corresponding spectrum readily obtained as the Fourier transform of a classical trajectory shows that the fundamental frequency is shifted to lower values owing to the anharmonicity of the potential. We observe also a substructure of combination lines generated by a nonlinear resonance with the intermolecular mode. These properties are consistent with experimental observation. In a four-atoms model, the lines are split when intramolecular Fermi resonance occurs. When the intermolecular mode becomes chaotic there is no vibrational heating of the intramolecular neighboring mode which tends to behave like a local isolated oscillator.
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  • 61
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    International Journal of Quantum Chemistry 34 (1988), S. 85-86 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 62
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    International Journal of Quantum Chemistry 34 (1988), S. 87-87 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 63
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    International Journal of Quantum Chemistry 34 (1988) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 64
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    International Journal of Quantum Chemistry 34 (1988), S. 121-131 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new and very simple one-range expansion of the 0s function is derived and employed as the starting point of three recurrence relations which allow the expansion of arbitrary Slater functions over displaced centers. Convergence of the expansions, both pointwise and in norm, are analyzed, and three-center nuclear attraction integrals are chosen for a further test of the formal developments and the numerical behavior of these expansions.
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  • 65
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    International Journal of Quantum Chemistry 34 (1988), S. 193-193 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 66
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    International Journal of Quantum Chemistry 34 (1988), S. 207-216 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two molecular charge similarity index (CSI) methods are further evaluated for practical application: one method based on a simple CNDO-type approximation to the electron density function and the other based on an ab initio pseudo total charge density function. The test system consists of isosteric analogues of dimethyl ether and methoxy acetic acid. The effects of differences in skeletal structure on the CSI measure of electron density similarity about corresponding atoms is estimated, and two new developments are presented for application of the ab initio-based method: (1) an INDO-type approximation which improves the efficiency of the CSI calculation; and (2) a FOCUS feature which enables comparisons of local molecule regions.
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  • 67
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    International Journal of Quantum Chemistry 34 (1988), S. 247-266 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The distribution of energy levels of an N-identical-particle system among the irreducible representations of the permutation group is examined for a “spin-free” problem. There are calculated the sums of powers of the eigenenergies obtained from the original N!-fold degenerate energy level when the interaction between the particles is switched on. The first-order perturbation theory is applied. Some results of the present approach are shown to be equivalent to the results of the Weyl's theory of the permutation group. The distribution of energy levels is found to be symmetric with respect to the average energy level belonging to a self-conjugate representation. For a special case of the Coulomb interaction the wave function of the highest level is fully symmetric, whereas that of the lowest level is fully antisymmetric with respect to the interchange of the coordinates of any two particles. The average energy and the dispersion of the levels belonging to a given representation are calculated for some N.
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  • 68
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    International Journal of Quantum Chemistry 34 (1988), S. 289-300 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown how the properties of the one-particle Green's function lead naturally to the definition of the so-called natural energy orbitals. These orbitals allow the fully correlated total energy of a system to be written in Hartree-Fock-like fashion and might therefore provide a bridge between sophisticated correlated wave functions and approximate theories of chemical structure and reactivity based on a Hartree-Fock-like energy expression. Moreover these orbitals form the basis for a self-consistent scheme to calculate the one-particle Green's function. The relation between these natural energy orbitals and the extended Koopmans' theorem is considered. Finally it is shown that the exactness of the lowest extended Koopmans' ionization potential implies the linear independence of the corresponding Dyson orbital from all other Dyson orbitals.
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  • 69
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    International Journal of Quantum Chemistry 34 (1988), S. 309-323 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The shape wave u(r) is defined in such a way that the square of its absolute value gives the shape of the electron charge density for a nonrelativistic many-electron system: |u(r)|2 = ρ(r)/∫ρ(r) dr, where ρ(r) is the total electron charge density. The u(r) is treated as the probability amplitude for the shape of the electron charge density in the real three-dimensional space. The secular equation of the u(r) is given as L(r)u(r) = λu(r), where L(r) and λ are a real Hermitean operator and the eigenvalue, respectively. This equation has the form of the spinless one-particle Schrödinger equation. The potential is local and is a functional of ρ(r), and so we need a self-consistent field procedure to solve it. For equilibrium state shape wave u = ueq, which is temperature-dependent, and for stationary state shape wave u = u0, respectively, Leq(r)ueq(r) = λequeq(r) and L0(r)u0(r) = λ0u0(r). For one-electron systems, the latter equation reduces to the Schrödinger equation for a stationary state, with the usual eigenvalue λ0 = E0. In general, λ is identified with the Gibbs chemical potential μG. Boundary conditions such as the cusp condition at a nucleus and exponential decay at an infinitely large distance from the nucleus are easily implemented. In case L(r) allows complex eigenfunctions, u(r) = A(r)eiS(r), the hydrodynamical potential appears in the secular equation for the real amplitude A(r). The real phase S(r) satisfies the equation of continuity. By introducing «apparatus» operators [16], the excited state shape wave is also obtained. Comparisons are made with a recent discussion of Levy, Perdew, and Sahni [3].
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    International Journal of Quantum Chemistry 34 (1988), S. 401-406 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 71
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    International Journal of Quantum Chemistry 34 (1988), S. 67-84 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A class of thromboxane antagonists exists where the prostaglandin side chain containing the C16 hydroxyl moiety is replaced by a phenyl ring, and the bridged six-membered pyranose moiety by cyclohexane, pyranose and dioxane ring systems. Analysis of antagonist potency data in terms of a binding constant model previously used for membrane bound receptor-drug interactions shows that the major patterns of antagonist potency are governed as much by axial/equatorial conformer preference of the phenyl moiety and its orientation as by electrostatic effects of the aliphatic ring oxygen atoms. The conformational restriction of the two substituted side chains of the σ-bonded 6-membered ring is shown to be a primary requirement for binding to thromboxane receptors, and a quantitative separation of electrostatic and conformational components in the potency data is attempted.
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  • 72
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    International Journal of Quantum Chemistry 34 (1988), S. 119-135 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations have been performed to investigate hydrogen bonding and ion-molecule association in complexes of H2O with the neutral, protonated, and Li+ complexes of N-formylformaldehyde and N-formylformamidine. In the complexes with the neutral bases, H2O assumes an in-plane bridging position in the amide and amidine regions. The most stable complex is the bridging N-formylformamidine-H2O complex in the amidine region, which has an MP2/6-31 + G(d,p) binding energy of -9 kcal/mol. Hydrogen bonded complexes of H2O with the oxygen-protonated bases have open structures with the protonated bases as proton donors, and binding energies ranging from -16 to -24 kcal/mol. Nitrogen protonation of N-formylformamidine leads to an equilibrium chelated hydrogen bonded structure with a stabilization energy of -21 kcal/mol. When Li+ associates with these bases at a carbonyl oxygen, hydrogen-bonded bridging structures with H2O reappear, and wobble complexes exist in the amide and amidine regions of N-formylformaldehyde and N-formylformamidine. These complexes have binding energies of -13 to -14 kcal/mol. However, the most stable comples has H2O directly bonded to Li+, with an MP2 binding energy of -30 kcal/mol. No hydrogen bonded structures of H2O with N-formylformamidine exist in the amide region when Li+ associates with this base at the C=N group. Hydrogen bond energies computed at the single-determinant Hartree-Fock level with the 6-31G(d) basis set approximate correlated MP2/6-31 + G(d, p) energies to within 1 kcal/mol for all of the neutral and charged complexes. However, when H2O is bonded to Li+, HF6-31G(d) association energies overestimate MP2/6-31 + G(d, p) energies by 3 kcal/mol.
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  • 73
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    International Journal of Quantum Chemistry 34 (1988), S. 301-304 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of the boundary conditions is emphasized in determining the relation between the counting problem, posed by Coulson and solved by the number theorists, and the physical problem from which it arises. The surface energy term, which Coulson sought, does exist, but only when the periodic boundary conditions, which he used, are replaced by the finite box conditions.
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  • 74
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    International Journal of Quantum Chemistry 34 (1988), S. 325-332 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The graph theory of molecular orbitals including second neighbor interactions (η) is considered here. Graphical methods of getting the characteristic polynomial for the π system of a conjugated molecule are given. It is shown that the characteristic polynomial can be factorized if there are symmetries in the molecule.
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  • 75
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    International Journal of Quantum Chemistry 34 (1988), S. 375-383 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calculations have been made at the minima of the X1A1 ground state of the ozone molecule. The equilibrium geometries have been obtained by means of CID calculations. The criterion adopted for the choice of configurations gives realistic results. CIPSI calculations at the two minima lead to an estimated gap of 0.92 eV between them.Our results agree with the analysis of previous theoretical works on the relative stability of open and cyclic zone structures, showing that the D3h minimum is stable relative to the ground state dissociation limit.
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  • 76
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    International Journal of Quantum Chemistry 34 (1988), S. 407-415 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ground state energies of finite Hubbard molecules are calculated by numerically solving the Lieb-Wu equations for a complex Hubbard repulsion parameter U. From the positions of the singular points located in the complex plane, the radii of convergence of the perturbation expansions for the ground state energies are determined.
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  • 77
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    International Journal of Quantum Chemistry 34 (1988), S. 445-455 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple procedure has been created for indexing the spin-free configurations of an N-electron system in spin state S. This indexing has been linked to a procedure for generating the matrix representations of the generators of the unitary group U(n) to enable a direct configuration study to be undertaken.
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  • 78
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    International Journal of Quantum Chemistry 34 (1988), S. 485-486 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 79
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    International Journal of Quantum Chemistry 34 (1988), S. 509-515 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A perturbation expansion which connects the hydrogenic limit energy density functional to the Thomas-Fermi functional is discussed. This perturbation series, where the Coulomb energy density functional is treated as the perturbation to the hydrogenic limit functional, is, in fact, the q = (N/Z) expansion of Thomas-Fermi theory. A truncated form of the first-order correction to the functional provides further insight into the model which treats the ground state energy as a local functional of the electron density.
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  • 80
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    International Journal of Quantum Chemistry 34 (1988), S. 103-118 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A formalism for a computational treatment of the polarization of a solvent and polar solutes immersed in it is presented. The solvent is modeled as a continuum dielectric. Polarization effects are represented by a polarization charge density at the dielectric boundaries and by induced dipoles at the polarizable atoms. Applications of this formalism with nonpolarizable atoms have led to excellent agreement between the calculated and experimental hydration enthalpies of a variety of polar molecules. A problem of the choice of the charge distribution of the solute is addressed in calculations of the solution dipole moment and hydration enthalpy of polarizable molecule of water in solution. Experimental values of these properties were well reproduced in calculations starting with point charges fitted to the vacuum dipole moment of the water molecule. Tests calculations for spherical models and for a 13-residue peptide show good convergence of the computational method. It is shown in calculations on simplified models that a change in the exposure of a charged side chain can lead to large changes in the potential inside protein measured at a fixed distance from the charge and at the same depth from the protein surface. Calculations performed for the C-peptide of the ribonuclease suggest that the differential screening of partial charges can reverse the sign of the vacuum potential of the helix dipole.
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  • 81
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    International Journal of Quantum Chemistry 34 (1988), S. 167-178 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present models for the interaction of glucocorticoids: dexamethasone (DEX), dexamethasone-21-mesylate (DEXM) and deacylcortivazol (DAC) with the hexanucleotide sequence d(TGTTCT)2 (CORE sequence) found in the long terminal repeat of MMTV. These models are obtained by computer-aided geometry simulation with energy minimization technique, making use of the empirical potential energy functions. We have considered both intercalative and nonintercalative binding. Differences in the glucocorticoid activity of these steroids are explained on the basis of stereochemical and energetic differences. A model is proposed for interaction of the steroid-receptor complex with the hormone-responsive element (HRE).
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  • 82
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    International Journal of Quantum Chemistry 34 (1988), S. 191-199 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently, one of the members of this group (Fritz) has observed some unusual properties of rouleaugenic polymer solutions. It was found that the diffusion coefficient of polystyrene spheres in these solutions displayed an expected fall followed by an unexpected rise in values when the radii of these particles are changed. In this paper we present some of these experiments and provide a thermodynamic interpretation of the rise in the values of the diffusion coefficient.
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  • 83
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    International Journal of Quantum Chemistry 34 (1988), S. 235-245 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Data and analyses are presented on the first synthetic polypeptide system to exhibit mechanochemical coupling; the mechanochemical coupling can also be demonstrated to be both polymer-based and solvent-based with respect to where the result of the change in the chemical potential is focused. Both polymer-based and solvent-based processes are the result of chemomechanical transduction in which the change in chemical potential results in a change in the temperature at which an inverse temperature transition occurs. In the polymer-based process, the contraction/relaxation occurs due to a change in the chemical nature of the polypeptide; in the solvent-based process there is no change in the chemical nature of the polypeptide on contraction or relaxation, but rather the change in chemical potential changes the state of hydration of the polypeptide. The new mechanochemical system provides an experimental system with which to clarify and to quantitate what may be called aqueous mediated apolar-polar interaction energies in polypeptides and proteins with hydrophobic groups that may be variously exposed to the aqueous solution or buried within the folded polypeptide or protein. Furthermore, it is noted that any conformational change exhibited by a polypeptide or protein that is the result of a binding of a chemical moiety, the change in chemical nature of a bound moiety or the change in chemical potential of the medium can be viewed in terms of mechanochemical coupling or chemomechanical transduction.
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  • 84
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    International Journal of Quantum Chemistry 34 (1988), S. 275-285 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modified cluster approach for modeling local chemisorption phenomena is suggested on the basis of the linear combination of Gaussian-type orbitals (LCGTO) Xα method. Contractions of the fitting bases are employed to take into account the reduced polarizability of a surface cluster and to access larger cluster sizes. Furthermore, embedding of a cluster in the surface is mimicked by Gaussian broadening of the one-electron levels leading to fractional occupation numbers via a self-consistently determined Fermi energy of the cluster. As a first application results are presented for the clusters NinNa (n = 5, 9, 17) modeling the low coverage limit of the chemisorption system Ni(100)/Na. Calculated bond length, binding energy, and induced “surface” dipole moment show fair agreement with experimental values, indicating a substantial covalent character of alkali bonding on transition metal surfaces even in the zero coverage limit.
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    International Journal of Quantum Chemistry 34 (1988), S. 319-328 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectra and characteristic polynomials of polyhedral cluster graphs containing 4-120 vertices are obtained. Some of the polyhedral graphs considered such as icosahedron, Archimedene etc., are models for some interesting clusters such as C120. For the Archimedene the spectra and delocalization energies are obtained with and without bond alternations. The characteristic polynomials and spectra of all the polyhedral clusters considered in this investigation are unique.
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  • 86
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    International Journal of Quantum Chemistry 34 (1988), S. 383-405 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The multireference many-body perturbation theory (MBPT) method is presented pedagogically. The distinctions between complete and incomplete model spaces are discussed. All second- and third-order diagrams for the diagonal and off-diagonal elements of the effective Hamiltonian matrix are presented in a compact form for complete and incomplete model spaces, including a new treatment of the renormalization diagrams. Illustrative numerical results are presented for the excitation energies of C2H4 using an incomplete single excitation model space, and for a study of FH potential energy surfaces with several different sizes of reference space.
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  • 87
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    International Journal of Quantum Chemistry 34 (1988), S. 457-463 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dirac-Fock balanced Gaussian basis calculations that employ an extended nucleus model (see Ref. 11) have been performed on Be and Ne atoms by systematically enlarging the basis set. As expansion size increases, the total energy smoothly converges toward the numerical Dirac-Fock limit from above. The balanced expansion method does not introduce any of the variational instabilities that have plagued the early Dirac-Fock basis expansion calculations.
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  • 88
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    International Journal of Quantum Chemistry 34 (1988), S. 481-490 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Generator Coordinate Approximation (GCA) is the general approximation scheme for molecular systems devised to improve the Adiabatic Approximation (AA). This is achieved by replacing the familiar product-type molecular wave function by a convolution product-like state. One can demonstrate via Born-Oppenheimer perturbation theory that for vibration-rotation levels near potential energy minima the GCA results are bracketted by the exact and adiabatic values, subject to the use of good quality electronic states as input (e.g., the Hellman-Feynman theorem needs to be satisfied accurately). We investigate the relevance of the GCA for energy levels near avoided crossing regions using a system modeled on the EF 1Σ+g state of hydrogen. The results of numerical experiments on this system are very encouraging (80-90%) of the nonadiabatic effects is recovered. This numerical success awaits theoretical explanation.
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    International Journal of Quantum Chemistry 33 (1988), S. 279-300 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We analyze the theoretical basis of a procedure to determine an unknown normalization factor in discretized wave functions, which we have successfully used in a series of calculations of resonance widths for atomic and molecular systems. By reducing this determination to that of a suitable interpolation function for the energy eigenvalues, the problem is easily solved when atomic basis sets are chosen according to simple rules. Illustrations of our procedure are presented for atomic, molecular, and model systems; renormalized wave functions are compared with the exact ones for these model systems. The resulting method of renormalized continuum wave functions has a wide range of application in the study of long-lived quasibound states (predissociation, autoionization, photoionization, unimolecular reactions, etc.).
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  • 90
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    International Journal of Quantum Chemistry 33 (1988), S. 349-367 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transmission of vibrational excitation energy conserved in cis-conformation of retinal to the outlet proton channel is considered from the perspective of quantum theory. A distribution of vibrational excitations in the channel is found; it allowed to calculate the magnitude of the directed drift proton current. The differences between velocities of proton movement in active and passive channels are considered. A transition of retinal from cis- to all -trans- conformation with the subsequent capture of proton by Schiff base out of the inlet channel is described. The lack of proton in this channel, i.e., in the H-bonded chain, is eliminated at the expense of the capture of a proton out of the cytoplasmic water enviroment. The correspondence between theoretically established states and spectroscopically identified forms of bacteriorhodopsin (inter-mediates L, M, N, and O) is proposed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 91
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 395-401 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparison of different many-body perturbation theory (MBPT) calculations of the ground state rotational and vibrational constants of SiS is made. The calculations are performed up to the complete fourth-order MBPT level, and in all cases two basis sets are utilized. The results of the third-order and some incomplete fourth-order calculations are in good agreement, but the complete fourth-order is among the worst as compared with the experimental data. Analysis of the different contributions to the calculated correlation eneriges points towards the necessity of including even higher-order terms of the(MBPT) expansion.
    Additional Material: 1 Ill.
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  • 92
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 403-443 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The partitioning of the vibrational-electronic Hamiltonian is presented. This partitioning is based on a new quasiparticle transformation that is constructed in such a way that the adiabatic approximation is included into the unperturbed Hamiltonian; nonadiabacity, anharmonicity, and electron correlation are treated as perturbations. We also present the second quantization treatment for bosons. The many body perturbation theory expansion for the vibrational-electronic Hamiltonian is suggested. A comparison of this approach is made with gradient techniques.
    Type of Medium: Electronic Resource
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  • 93
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 479-479 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 94
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 73-84 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two-dimensional (2D) band structure of (polyphthalocyaninato)Ni(II), Ni(ppc), has been analyzed by a self-consistent field (SCF) Hartree-Fock (HF) crystal orbital (CO) formalism based on an INDO (intermediate neglect of differential overlap) type Hamiltonian. The calculated HF band gap of Ni(ppc) amounts to 0.24 eV. The highest filled band is a ringlike a1u combination (D4h symmetry label) localized at the carbon sites of the organic fragment. Remarkable hybridization in the valence band leads to the considerable band width Δ∊v of 2.92 eV. This value is close to the Δ∊v numbers which are conventionally encountered in one-dimensional metallomacrocycles. The effective width of the states in Ni(ppc) is 13.8 eV. In graphite a net π interval of 13.0 eV is predicted by the present CO formalism; i.e., the energetic distribution of the π electrons is roughly comparable in both 2D solids. The Ni 3d states in Ni(ppc) are far below the Fermi level which is calculated at -4.9 eV; they are predicted between -12.2 and -16.4 eV in the mean-field approximation. Quasi-particle corrections lead to a significant shift of these strongly metal-centered states. Important electronic structure properties of Ni(ppc) are compared with those of 1D metallomacrocycles with similar molecular stoichiometry. The total density of states distribution of Ni(ppc) has been fragmented into projected (ligand π and σ, Ni 3d) contributions in order to allow for a transparent interpretation of the 2D band structure.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 95
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A set of 20 nitropolycyclic aromatic hydrocarbons, whose mutagenicity has been determined in the Ames test, has been studied using octanol-water partition coefficients (P) as a measure of relative hydrophobicity and molecular orbital energies to account for variation in their electronic characteristics. A good structure-activity relationship was found using log P and ∊LUMO. The latter were taken from the results of ab initio calculations performed by Maynard, Pedersen, Posner, and McKinney [7] and were also calculated by the MNDO method. The dependence of mutagenicity on hydrophobicity was found to be similar to that observed for triazenes [2]. ∊LUMO values calculated by MNDO and STO-3G were found to be strongly correlated, and the role of hydrophobicity in correlating mutagenicity was not significantly affected by the molecular orbital model employed.
    Additional Material: 4 Tab.
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  • 96
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 103-106 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Finiteness is usually imposed as a condition for physical admissibility of a wave function. Examination of this condition in both position- and momentum-space shows that finiteness of the wave function at the origin in one space implies “linear” integrability in the reciprocal space, except in some pathological cases. Some implications of this result are discussed.
    Type of Medium: Electronic Resource
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  • 97
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 217-224 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The theory of the Baker-Gammel approximants is applied to the spectral density function associated with the adjacency matrix. As a result, various upper and lower bounds to topological invariants are obtained in a systematic manner. In particular, the (N, M)-type lower bound to the total π-electron energy of benzenoid hydrocarbons is derived for the first time.
    Additional Material: 3 Tab.
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  • 98
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 179-190 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydration-free energy, energy, and entropy of monovalent ions are calculated using the extended RISM integral equation theory and computer simulations. Plots of these thermodynamic quantities against 1/R, where R is the Lennard-Jones radius, lie on two distinct curves corresponding to cations and anions. This result is attributed to differences in the microscopic structure of solvent surrounding the ions. Charge distribution functions are used to analyze solvent structure. It is found that the modified Born formula proposed by the Latimer et al. gives good agreement with the RISM results for the energy and the free energy, but not for the entropy. A microscopic interpretation of Latimer formula is attempted in light of the statistical mechanical theory.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 99
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Since the introduction of dynamical simulated annealing (DSA) by Car and Parrinello in 1985, there has been growing interest in the use of nonlinear optimization to perform electronic structure calculations. We review here the complementary method of steepest descents (SD), a first-order treatment designed for local optimization. Modifications are discussed to adapt SD to a supercell treatment of metallic systems using a plane wave basis. An application to the Zintl phase compound NaTl is presented. The application of separable nonlocal pseudopotentials to improve this momentum space formalism is discussed.
    Additional Material: 1 Ill.
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  • 100
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 245-255 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural and energetic results are reported from a series of ab initio calculations on ground state CuCl2-4 in D2d and D4h conformations. All-electron Hartree-Fock calculations including geometry optimization have been carried out with large basis sets reaching triple-zeta valence plus f-function quality. Several ab initio effective core potentials and valence basis sets for Cu and Cl have been tested and evaluated based on comparisons of calculated results obtained at the Hartree-Fock or correlated (Moller-Plesset perturbation theory) levels with the all-electron and experimental data. The optimized structural parameters provided by all-electron or effective core potential methods are very similar, but they differ from averaged experimental data. Thus, the calculated CuCl bond lengths are typically 0.15-0.20 Å too large, and the ClCuCl bond angle (D2d) is 10-15° too small. The square planar (D4h) conformation represents a transition state and not a structural minimum for CuCl2-4. The energy difference between the two conformations (D4h - D2d) is consistently 16-18 kcal/mol at the Hartree-Fock level but approaches 10-12 kcal/mol at the highest levels of theory applied (UMP4(SDTQ)).
    Additional Material: 3 Tab.
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