摘要:

The molecular orbital theory is adapted to the calculation of magnetic shielding constants in aromatic molecules. The usuallcaoperturbation theory is generalized to take account of the imaginary perturbation due to an external magnetic field. The induced field at a point is then calculated by inserting a test dipole, adopting approximations due to London, and using the perturbation theory to evaluate a coupling energy. The results differ somewhat from those obtained in a rather different manner by Pople.

ISSN:0026-8976    

DOI:10.1080/00268975800100381

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

The paramagnetic contributions to the susceptibilities of compounds of B-subgroup ions and the chemical shifts observed in their nuclear magnetic resonance spectra are shown to depend on interconfigurational mixing brought about by environments of less than cubic symmetry. Order of magnitude calculations are made for Pb2+compounds and agree reasonably well with experiment.

ISSN:0026-8976    

DOI:10.1080/00268975800100391

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

Indirect spin-spin couplings between methyl groups attached to unsaturated organic molecules and protons directly bonded to unsaturated carbon atoms have been observed in several molecules. An attempt is made to account in a qualitative way for the observed spin-spin couplings by ascribing them largely to hyperconjugation between methyl group orbitals andπ-electron orbitals. The connection of these observations with electron spin resonance spectra is mentioned.

ISSN:0026-8976    

DOI:10.1080/00268975800100401

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

High resolution hydrogen resonance spectra are given for a number of asymmetrically trisubstituted derivatives of benzene. In some cases the spectra can be analysed as AB2, ABB′ or ABX cases. The ABB′ case, in which the B nuclei have identical chemical shifts but are unequally coupled to A, is discussed and illustrated. The spin-spin coupling constants between protons (a) ortho to one another lie in the range 7 to 9 c/s, (b) meta to one another occur near 2·5 c/s and (c) para to one another are less than 1 c/s.

ISSN:0026-8976    

DOI:10.1080/00268975800100411

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

A formula is derived for the integrated intensity of pressure-induced rotational transitions in pure gases and gas mixtures at moderate pressures. This formula is applied to the pressure induced rotational spectrum of hydrogen, described in a previous article. A good agreement between the observed and the calculated intensities can be obtained if it is assumed that the induction of the transition moments is mainly caused by the quadrupole field of the hydrogen molecule. In an analogous way, the intensity of the induced simultaneous vibrational-rotational transition in mixtures of carbon monoxide and hydrogen is calculated.

ISSN:0026-8976    

DOI:10.1080/00268975800100421

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

Calculations have been performed on the probabilities of triplet-singlet transitions in benzene and acetone in connection with the decay times of the phosphorescence. The transition probability was determined from the extent to which excited singlet states are mixed with the triplet state. The assumption that in benzene the phosphorescent state has3B2uproperties—so that the1B1usinglet state is mixed with it-—yields the best agreement with the experimental data. In the case of acetone the phosphorescence was considered as a triplet-singlet transition in which only the electrons of the CO group are involved. In both cases the agreement with experiment is as satisfactory as in other calculations on transition probabilities, the figures for the decay times being 190 and 7 seconds for benzene and 7·8 and 0·6 milliseconds for acetone. The ratio of the calculated decay times is in good agreement with the experimental result (2·4×104and 1·2×1O4).

ISSN:0026-8976    

DOI:10.1080/00268975800100431

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

The observations of Dressler and Ramsay on the vibronic absorption spectrum of the NH2radical are interpreted quantitatively in terms of the Renner effect. The use of a perturbation method leads to frequency predictions which are in good accord with experiment and confirm the view of these authors that the absorption band is associated with transitions between the components of an electronic II state which are widely separated by electronic-vibrational interaction.

ISSN:0026-8976    

DOI:10.1080/00268975800100441

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

The π-electron spectra of the nitrogen heterocyclics are discussed on the basis of a perturbation applied to the spectra of the corresponding aromatic hydrocarbons. The frequency of the first π→π band in pyridine is the same as that of the corresponding band in benzene, because of the accidental cancellation of a first-order blue shift by a second-order red shift. The first-and second-order shifts are related to two perturbation parameters, and these are obtained from experiment by examining the spectra of the benzene heterocyclics. These parameters can then be satisfactorily related to one another by assuming a perturbation field of the form exp (−2ηr)/rand by allowing for the C-N bond being shorter than the C-C bond in benzene.

ISSN:0026-8976    

DOI:10.1080/00268975800100451

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

The infra-red spectra of KH2PO4, NH4H2PO4, NaH2PO4, KH2AsO4, NH2H2AsO4, Ag2H3IO6and (NH4)2H3IO6and of their deuterated analogues have been recorded at room temperature and some of them also at low temperature in the ferroelectric phase. The interpretation of the particularly interesting spectral region between 3000 and 1500 cm−1, containing several OH bands, has been made in terms of the tunnelling of the protons between two minima of potential energy. These were taken to be of equal depth in the non-ferroelectric phase and unsymmetrical in the ferroelectric form. A quantum-mechanical treatment of the vibrational problem of the latter type has been carried out and is presented in the Appendix. Good agreement has been found between the theoretically predicted energy levels and the experimental data.

ISSN:0026-8976    

DOI:10.1080/00268975800100461

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor

摘要:

Carbon-13 hyperfine splittings equal to 41±3 gauss have been observed in the paramagnetic resonance of a mixture of C12H3and C13H3radicals produced by x-irradiation of CH3I at 77°k. The observed splitting provides strong evidence that CH3is a planar molecule.

ISSN:0026-8976    

DOI:10.1080/00268975800100471

出版商:Taylor & Francis Group    

年代:1958

数据来源: Taylor