摘要:

An independent electron molecular orbital theory of diamagnetism is used to calculate carbon chemical shifts for some simple molecules characteristic of important organic groups. The molecules considered are ethane, ethylene, acetylene, allene, carbon disulphide, carbonate and formaldehyde. The theory predicts (1) a low field shift for molecules with low electronic excitation energies, (2) a high field shift if the carbon atom has high electron density, and (3) a multiple bond effect which may be estimated from molecular orbital bond orders between neighbouring atoms. It is shown that reasonable quantitative assumptions about these three effects in the molecules considered lead to calculated chemical shifts in satisfactory agreement with experimental data.

ISSN:0026-8976    

DOI:10.1080/00268976300101061

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

The1H and19F resonance spectra of 1-fluoro-2,4-dinitrobenzene in pure liquid and in 5 mole per cent solutions in benzene and acetone were obtained and analysed by an iterative computer calculation. The results for the pure liquid are in good agreement with perturbation calculations performed on this spectrum earlier. It is shown that the deviation between the values of coupling constants obtained earlier in benzene solution, acetone solution and pure liquid are not due to the method of analysis.

ISSN:0026-8976    

DOI:10.1080/00268976300101071

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

Methods introduced in a previous paper are used to calculate thegtensors of aromatic hydrocarbons. For even-alternant molecules made up of six-membered rings, it is predicted that the axes of thegtensor are the same for both ions, and that (gxx-gyy) is equal in magnitude and opposite in sign for the two ions, where thezaxis is perpendicular to the molecular plane. Such molecules in their lowest triplet states, and all neutral odd-alternant radicals, are predicted to havegxx=gyy= 2·0027,gzz= 2·0024.

ISSN:0026-8976    

DOI:10.1080/00268976300101081

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

It is shown that the nitrogen hyperfine coupling parameters for nitric oxide radicals depend on the solvent. An equilibrium constant is calculated for the interaction of diphenyl nitric oxide andp-p′-dianisyl nitric oxide with di-tert-butyl peroxide andtert-butyl hydroperoxide in a mixture of the two solvents. By plotting the nitrogen splitting found in the peroxide against that in the hydroperoxide for a series of nitric oxide radicals a straight line is obtained and a tentative theoretical treatment is given to account for this based on the equation of Karplus and Fraenkel. Similar results are shown to hold for thepara-substituted nitrobenzene anions.

ISSN:0026-8976    

DOI:10.1080/00268976300101091

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

In dealing theoretically with the effects of vibronic interactions in substituted benzene mononegative radical-ions it is useful to know the spin density distributions in the degenerate ground level of unsubstituted benzene anions. A configuration interaction theory is developed for hydrocarbon anions with degenerate ground states and applied to the benzene anion problem. The results show negative spin densities on atoms having zero spin density in the Hückel approximation.

ISSN:0026-8976    

DOI:10.1080/00268976300101101

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

It is shown that the splitting constants observed for methylenic protons in π-electron radicals can be accounted for by hyperconjugation only. The theory predicts correctly both magnitude and the ratio of the splittings in the positive and negative ion of pyracene. Application of the method to the negative ion of acenaphthene and the cyclohexadienyl radical also yields satisfactory results.

ISSN:0026-8976    

DOI:10.1080/00268976300101111

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

An equation of state is obtained in closed form for a gas composed of molecules with Lennard-Jones (n,1/2n) potentials. It is useful at temperatures above about 12 (ε/k), where -εis the minimum energy of interaction and at all densities at which the equilibrium state is a fluid. It is derived by summing over all the cluster integrals of the virial expansion that occur in the approximation for the pair distribution function proposed by Percus and Yevick. Each cluster integral is represented correctly to terms of the order ofn-1.

ISSN:0026-8976    

DOI:10.1080/00268976300101121

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

The changes of the electronic transition energies which occur on dimerization of naphthalene, anthracene, pyrene and perylene, have been calculated. It has been found that the observed spectral changes cannot be understood unless the overlap of orbitals of the two monomers is included in the calculation. Good agreement between the observed and calculated fluorescence spectrum is obtained if it is assumed that in the fluorescent state of the dimer the interplanar separation of the monomers is approximately 3å.

ISSN:0026-8976    

DOI:10.1080/00268976300101131

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

The theory of electrical images is used to derive Van der Waals forces at the surface of a solid, which is treated as a continuous dielectric medium. The theory gives the attraction between a single atom and the surface, between two atoms which are both close to the surface and between two bodies separated by a gap. The forces come out in terms of the dielectric constant of the solid and the electric polarizability of the atom at imaginary frequencies. The method of images breaks down at distances greater than about 500å, and an exact treatment of the electromagnetic field fluctuations near the surface leads to the same force as Lifshitz's general theory.

ISSN:0026-8976    

DOI:10.1080/00268976300101141

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor

摘要:

The transition complex method is used for calculating the rate constant of non-adiabatic vibrational deactivation of diatomic molecules in the2II electronic state upon collisions with inert gas atoms. The main contribution to the rate constant comes from vibronic transition caused by spin-orbital and orbital-rotational couplings. The two-dimensional Landau-Zener approximation is considered in connection with calculation of the nonadiabatic transition near the crossing line of two potential surfaces, and the limitations of ideas concerning the activated complex are discussed. The general expression for the rate constant derived from the diatomic molecule-atom collision is correlated with that for the atomic collision.

ISSN:0026-8976    

DOI:10.1080/00268976300101151

出版商:Taylor & Francis Group    

年代:1964

数据来源: Taylor