摘要:

AbstractThe energies of hydrogenation of a series of alkenes have been calculated using both the 4‐31G and 6‐31G* basis sets. The inclusion of polarization functions leads to only a small change in calculated energy for simple alkenes but a large change is found with the more highly strained compounds. The calculated enthalpies of hydrogenation have been compared with experimental values and show that the error in the calculation is essentially constant (6 ± 2 kcal/mol). This makes it possible to estimate the enthalpies of formation and strain energies of the small ring alkenes for which experimental data are not available. The calculated structures of the compounds also are discu

ISSN:0021-2148    

DOI:10.1002/ijch.198300011

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe electronic structure of the lowest singlet and triplet states of cyclopropyne have been investigated usingab initiomolecular quantum mechanics. Both double zeta (DZ) and double zeta plus carbondfunction (DZ +d) basis sets have been used in conjunction with self‐consistent‐field (SCF), multiconfiguration (MC) SCF, and configuration interaction (CI) methods. Singlet cyclopropyne is predicted to be a transition state for the degenerate rearrangement of propadienylidene (H2C=C=C:). However, triplet cyclopropyne is a minimum on the C3H2potential energy hypersurface and vibrational frequencies are predicted at two levels of theory. Structures and vibrational frequencies are compared with those of the relatively stable cyclopropene molec

ISSN:0021-2148    

DOI:10.1002/ijch.198300012

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractFully optimized STO‐3G SCF MO calculations were conducted on a series of methyl substituted ethylene radical cations. The stabilizing effect of a methyl group is found to be 14 kcal/mol using ethylene as a reference. Analysis of the orbital make‐up of the radical cations and their calculated geometry suggests that hyperconjugative 1‐, 2‐, and 3‐electron interactions between the alkyl groups and the π‐system is largely responsible for the stabilization. Analysis of hyperconjugation in propene suggests that 2‐electron stabilization outweighs 4‐electron destabilization energetically but that effects of the 2‐electron stabilization are manifested in a low‐l

ISSN:0021-2148    

DOI:10.1002/ijch.198300013

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractAb initioconfiguration interaction (CI) calculations have been carried out in order to determine the energy difference between3Aî2trimethylenemethane (TMM) and1Agbutadiene. The pi CI value of 38.3 kcal/mol is very similar to the CI values obtained when excitations of the sigma electrons are permitted. This finding suggests that correlation effects involving sigma orbitals make at most a small contribution to the energy differences between non‐Kekulé hydrocarbon diradicals and their closed‐shell isomers. Possible complications in the experimental measurement of this energy difference are discussed. It is pointed out that methylenecyclopropane might be formed in attempts to deprotonate the 2‐methallyl cation, without the involvement of TMM. From the experimental heats of formation of methylenecyclopropane and butadiene, an energy difference of 14–16 kcal/mol between3Aî2TMM and methylenecyclopropane is estimated. This is in excellent agreement with a previous energy difference obtained by direct c

ISSN:0021-2148    

DOI:10.1002/ijch.198300014

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe preferred ground state conformation of β‐substituted ethyl radicals, with the Cβheteroatom substituent group being PH2, SH and CI1have been determined byab initiospin‐unrestricted self‐consistent field gradient optimization techniques. All the ground state geometries are found to have the Cβ‐heteroatom bond coplanar with the Cα‐centered radical orbital. No tendency towards heteroatom group bridging between Cαand Cβis found in the systems studied here. The radical centers are calculated to be non‐planar, with the Cαhydrogen atoms tilting towards the Cβsubstituent group. Calculated rotation energy profiles about the Cα‐Cβand Cβ‐heteroatoms bonds, as well as the atomic orbital spin population distributions, are interpreted in terms of possible interactions between the Cα‐centered radical orbital and the Cβ‐heteroatom σ bond orbitals (hyperconjugation, type I) or the heteroatom 3d(type II) or lone pair (type III) atomic orbitals. Type I is the only significant stabilizing interaction found in these systems, whereas the type III (two orbital, three electron) interaction is a

ISSN:0021-2148    

DOI:10.1002/ijch.198300015

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractNatural correlation diagrams have been established to describe hydrogen photoabstraction in ketones and thiones for three different reaction paths (nx, πxand πcapproaches). Their conclusions have been confirmed byab initioSCF‐CI calculations. This procedure leads to the following conclusions: Energy barriers exist on the potential energy surfaces of all the potentially reactive excited states. The height of these barriers is strongly dependent on the distance separating the hydrogen acceptor and hydrogen donor atoms in the transition state. For thenapproach, the reactive channel only involvesnπ* excited states while, for the π approach,nπ* (hydrogen capture by the carbon atom) and ππ* (hydrogen capture by the oxygen or the carbon atom) excited states must also be taken into consideration. A proposal for resolving the ketone‐thione dichotomy is presented on the basis of the

ISSN:0021-2148    

DOI:10.1002/ijch.198300016

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe spectrum of rotations about single bonds has been divided into two different groups of processes, termed TAand TC. These describe interconversion of planar ground state conformations (as in amides), and interconversion of enantiomers (as in sulfenamides and hydroxylamines), respectively. A frontier molecular orbital analysis of the hydrazyl cation and anion reveals that a change in electron occupancy alone can bring about a change from one torsional process to the other. Thus, the four‐electron hydrazyl anion undergoes a TCprocess, while the corresponding two‐electron cation undergoes a TArotation. Nonempirical SCF‐MO calculations of the model cation and anion with geometry optimization at the 4‐31G level confirm the results of the PMO analysis. The calculations also reveal a preference for an inversion (IA) mechanism for the topomerization of the cation system over a torsional

ISSN:0021-2148    

DOI:10.1002/ijch.198300017

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractAb initiocalculations at the minimal, split valence and extended basis set levels, both with and without electron correlation corrections, were used to study the insertion of singlet silylene into ethylene to form silacyclopropane. The least motion C2vpath is symmetry forbidden and an artificial barrier of about 36 kcal/mol is found within C2vsymmetry. Relaxation of symmetry to C, eliminates the symmetry forbiddenness of the reaction. The 3‐21G and 6‐31G* SCF calculations still predict a small barrier along this symmetry allowed path; however, the addition of second order correlation corrections results in the prediction of an insertion process with no barrier. The overall ΔEfor the reaction is predicted by MP2/6‐31G*//3‐21G to be 47.9

ISSN:0021-2148    

DOI:10.1002/ijch.198300018

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe electronic structures of metal phthalocyanine polymers PcMX and MPc were examined by performing tight‐binding band calculations on PcMX (MX = SiO, GeO, AlF, GaF, CrF) and MPc (M = Ni, Co, Fe) chains. The present band structure study suggests that the electrical conductivities of halogen‐doped PcMX and MPc chains are governed by their valence bandsacomposed of the HOMOa1Mof each Pc ring. It is the valence bandathat becomes partially empty upon halogen‐doping. The Pc ring π‐orbitala1Mis made up of only the carbonporbitals. By symmetry, none of thes, panddorbitals of a metal atom M can mix into thea1Morbital. Consequently, the width of the valence bandais solely determined by such factors as the inter‐ring separation and the inter‐ring rotation. It was noted that there should be one, two and three unpaired electrons on each metal atom of CoPc, FePc and PcCrF chains, respectively. Thus halogen‐doped CoPc, FePc and PcCrF are expected to have magnetic properties associated with the unpa

ISSN:0021-2148    

DOI:10.1002/ijch.198300019

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractA number of ML4Lî complexes exist where Lî contains an electropositive atom connected to the transition metal. The structures of these compounds are very distorted; they do not correspond to a trigonal bipyramid, square pyramid or somewhere between these two extremes. An electronic rationale for these alternative structures is presented with the aid of molecular orbital calculations of the extended Hückel type. It is shown that in these compounds the M‐Lî bond is quite ionic in the sense of Lî+ML−4. The deformation is then due, in part, to the tendency of ML−4to adopt a tetrahedral arrangement. Furthermore, it is shown that an electrophile (Lî+) may attack a three‐fold face, two‐fold edge, or somewhere intermediate at the tetrahedral ML−4group yielding an alternative structure for these five‐c

ISSN:0021-2148    

DOI:10.1002/ijch.198300020

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY