摘要:

It is well known that in the fragment XHC1-HC2-HC3-HC4the vicinal coupling constant between a proton on C1and a proton on C2,J1v, decreases as the electronegativity,Ex, of the substituent atom, X, increases, and this has been explained in terms of the effects of rehybridization and induction which should vary monotonically down the fragment. However, fromJvtaken from the literature for a series of substituted hydrocarbons, it is apparent thatJ2vincreases withExwhileJ3vagain decreases asExincreases.

ISSN:0026-8976    

DOI:10.1080/00268976600100291

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The effect of stretching due to rotations and vibrations on the intermolecular potentials of diatomic molecules has been considered. The calculations for nitrogen and oxygen on the Lennard-Jones (12:6) model show that the effect is significant. Consequently, for polyatomic molecules the effect of stretching must be considered for a correct representation of the intermolecular potential.

ISSN:0026-8976    

DOI:10.1080/00268976600100301

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The θ-method, as applied to unsaturated hydrocarbons, is reformulated in terms of the iteration scheme used by McWeeny for solving the molecular self-consistent field equations. Results are given for the allyl and benzyl cations, fulvene and azulene. In all cases, the self-consistent charge densities are obtained without difficulty from a rapidly converging sequence of iterations. The calculations are further extended, using theory of Longuet-Higgins and Salem, to obtain self-consistency with respect to bond lengths.

ISSN:0026-8976    

DOI:10.1080/00268976600100311

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

Two formulae have been derived relating the E.S.R. hyperfine coupling constant of methyl and methylene group protons in aromatic radicals to the pi-electronic structure of the radical. The derivation of these formulae assumes that the principal coupling mechanism is hyperconjugation but includes a small spin polarization term. The formulae have been used to calculate theoretical methyl and methylene coupling constants in several radicals whose E.S.R. spectra have been measured.

ISSN:0026-8976    

DOI:10.1080/00268976600100321

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

Magnetic resonance spectra were recorded of glassy solutions of a number of positive aromatic ions in their triplet state, which theory predicts to be orbitally degenerate.

ISSN:0026-8976    

DOI:10.1080/00268976600100331

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The conditions under which N.M.R. spectra of organic free radicals can be observed are discussed. The N.M.R. spectra of several radicals are shown and compared with the E.S.R. spectra of the same radicals. The N.M.R. spectra are particularly useful to determine small coupling constants which are below the limit of resolvability of E.S.R. and ENDOR. Futhermore, N.M.R. renders the sign as well as the magnitude of the interaction between the unpaired electron and the nucleus investigated; it can contribute to the understanding of the mechanism of this interaction.

ISSN:0026-8976    

DOI:10.1080/00268976600100341

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

An approximate unrestricted Hartree-Fock method is used to calculate spin densities in the odd alternant radicals cyclohexadienyl, benzyl, perinaphthenyl and triphenylmethyl and the linear polyene radicals from allyl to C19H21. The results agree quite well with the exact calculations and with empirical estimates as well as with experimental data on hyperfine splitting constants and E.S.R. second moments.

ISSN:0026-8976    

DOI:10.1080/00268976600100351

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

An analysis is presented of the14N nuclear quadrupole coupling constants of pyridine,γ-picoline, pyrazine, tetramethylpyrazine, phenazine ands-triazine in terms of the populations of the sigma and pi bonding orbitals around the nitrogen atom. The limitations inherent in the interpretation of the quadrupole coupling data are discussed and it is shown that it is best used to determine the difference between the sigma and pi orbital populations. By assuming that the sigma orbital population remains constant for all these compounds values of the pi orbital populations are obtained and compared with the predictions of molecular orbital theories of various degrees of sophistication.

ISSN:0026-8976    

DOI:10.1080/00268976600100361

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

It is shown that the total collision cross section between two alkali atoms at a thermal velocityvis not given simply by the Massey-Mohr equation:

ISSN:0026-8976    

DOI:10.1080/00268976600100371

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The semi-empirical method due to Pariser and Parr [1] is extended to make it applicable to an axially symmetrical molecule. Wave functions are expressed in terms of atomic orbitals before deriving expressions for the matrix elements of the effective Hamiltonian, instead of the more usual method of first expressing the matrix elements in terms of integrals involving molecular orbitals; this is found to facilitate the treatment, in that it enables us to make more direct use of atomic valence-state energies. An empirical formula is derived for a one-centre integral which does not occur in the more usual applications of the Pariser-Parr method.

ISSN:0026-8976    

DOI:10.1080/00268976600100381

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor