摘要:

Allyl type radicals have been observed as the final irradiation products of both cyclohexene and cycloheptane included in thiourea. In the cyclohexene adduct the cyclohexenyl radical appears to be formed straight away, whilst in the cycloheptane adduct the cycloheptyl radical is formed first and, except at low temperatures where it is stabilized, changes to an allyl type radical without further irradiation.

ISSN:0026-8976    

DOI:10.1080/00268977000100011

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A frequency sweep proton-proton double-resonance study of spin relaxation is made in strongly coupled two spin systems (AB) formed by the protons in 2-bromothiazole (sample I) and in 2,3,4-trichloronitrobenzene (sample II). The single-resonance transitions of both these molecules exhibit broadening due to scalar coupling with nearby14N nuclei modulated by the rapid quadrupolar relaxation of the latter. A density-matrix analysis of double-resonance spectra obtained over a wide range of irradiation strengths coupled with a determination of14N resonance linewidths and approximate measurements of proton relaxation times leads to a determination of the spin-spin coupling constants of14N with the two protons, and the parameters describing the other mechanisms of proton relaxation in these molecules. It has been shown that a study of relaxation by double resonance is, in general, capable of yielding the relative signs of the coupling constants involving the14N nucleus. The results obtained may be summarized as follows:

ISSN:0026-8976    

DOI:10.1080/00268977000100021

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Literature data forδ(13C),δ(17O) andλn→π*maxfor carbonyl groups in various compounds are reviewed. In a wide variety of carbonyl compounds there is a linear relation betweenδ(17O) andgln→π*max. However, deviations from this general relationship occur for a group of ketones. The explanation is found in differences in electron-donating properties of the substituents at the carbonyl group, which cause changes in the electron density and in the polarity of the carbonyl group.

ISSN:0026-8976    

DOI:10.1080/00268977000100031

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A semi-empirical SCF molecular orbital method is developed in order to calculate rotational barriers and equilibrium conformations in the excited states of conjugated molecules. The new theory differs from the Pariser-Parr-Pople treatment in that differential overlap is neglected only when the atomic orbitals involved are not bonded to each other. Heats of formation and singlet excitation energies calculated with the modified theory agree well with the experimental values for a series of hydrocarbons and carbonyl compounds. The activation energy required for cis-trans isomerization in ethylenes is calculated as 62·3 kcal/mole, in excellent agreement with the experimental result of 65·0. Similarly, the energies of the planar and twisted forms of the lowest triplet of ethylene agree well with those obtained by the non-empirical calculations of Kaldor and Shavitt.

ISSN:0026-8976    

DOI:10.1080/00268977000100041

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

It is shown that in organic molecular crystals the fluctuations of the intermolecular electron jump frequencies resulting from the lattice vibrations may produce a considerable increase of the total electric current. An expression for the current density operator, which takes into account the electron-phonon interactions, is derived and the corresponding linear response theory of the electrical conductivity is formulated. The phonon-assisted current can be partially accounted for by the proper corrections of the electron velocities used in a simple band theory calculation. These corrections are explicitly calculated for a three-dimensional parabolic and a one-dimensional narrow electron energy band.

ISSN:0026-8976    

DOI:10.1080/00268977000100051

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A calculation is presented of the radiative lifetimes of theππ′phosphorescent state of quinoxaline and a number of aromatic hydrocarbons. For the matrix elements of the spin-orbit hamiltonian an ‘atoms in molecules’ approach is used and only the one-electron one-centre terms in the expansion of these matrix elements in integrals over AO's are retained. This approach is similar to that used by Goodman and Krishna for thenπ′states of some aza-aromatics. For quinoxaline a lifetimeτ=0·33 s is obtained.

ISSN:0026-8976    

DOI:10.1080/00268977000100061

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

(1 -σ)gIis the shielded nucleargvalue,g⊥, andg∥are the moleculargvalues perpendicular and parallel to the molecular symmetry axis;x⊥,x∥, σ⊥and σ∥are similarly defined elements of the magnetic susceptibility and the chemical shift tensors.

ISSN:0026-8976    

DOI:10.1080/00268977000100071

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A previously developed theory of the angular distribution and intensity of photoelectrons ejected from diatomic molecules is used to consider the potential information contained in rotational fine structure in molecular photoelectron spectroscopy. It is shown that resolution of such structure would permit the evaluation of contributions corresponding to the terms in a one-centre expansion of the molecular orbital from which the photoelectron is ejected. The case of H2is analysed in detail, and the analysis compared with that of Tully, Berry and Dalton.

ISSN:0026-8976    

DOI:10.1080/00268977000100081

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The origin band of the 2700 Å system of chlorobenzene has been rotationally analysed by the asymmetric rotor band contour method. It is shown to be a typeBband of a prolate asymmetric top which requires the electronic assignment of the system to be1B2-1A1. The excited state rotational constants are:A′=0·1797 ± 0·0001 cm-1,B′=0·05230 ± 0.00002 cm-1,C′=0.040512 ± 0.000007 cm-1. These can be interpreted in terms of a contraction of the C-Cl bond of about 0·04 Å and an expansion of the benzene ring similar to that in the1B2uexcited state of benzene. The origin of the 2700 Å band is shown to be at 37 048·2 ± 0·2 cm−1. Strong typeAbands involving theb2vibrationv29are also assigned from their rotational contours. The 291level is shown to be in Fermi resonance with the 141201level. Of the eight prominent sequence intervals associated with the origin band, five are interpreted with considerable certainty.

ISSN:0026-8976    

DOI:10.1080/00268977000100091

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The contact contribution to13C-H,13C-13C and to geminal and vicinal coupling constants is calculated according to Pople and Santry's theory using molecular orbital wave functions developed by Newtonet al.(NEMO wave functions). The calculated13C-H and13C-13C coupling constants are in better agreement with experiment than those obtained by the EHT or CNDO method. This must be due to the inclusion of carbon 1sorbitals in the LCAO basis set of the NEMO wave function.

ISSN:0026-8976    

DOI:10.1080/00268977000100101

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor