摘要:

Information about14N relaxation times and (N, F) coupling constants is obtained for three fluoropyridines from (a) a detailed band-shape analysis of the broad19F resonance bands assigned toortho-fluorine nuclei, (b)14N resonance bands, and (c)15N satellites in19F resonance. The effects of medium and of temperature were investigated, and activation energies for rotational diffusion are given. Double resonance experiments show that themeta(F, F) coupling constants for 3-chloro-2,4,5,6-tetrafluoropyridine vary in sign.

ISSN:0026-8976    

DOI:10.1080/00268977000101121

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A theoretical expression for the high-resolution nuclear resonance band shape of a group of magnetically equivalent spin-½ nuclei weakly coupled to other magnetically equivalent groups of spin-½ nuclei and to one quadrupolar nucleus is derived using Redfield's relaxation theory. The detailed treatment is carried out with the assumption that molecular reorientation is sufficiently rapid for the extreme narrowing approximation to be applicable. It is found that the overall band shape is expressible as a sum of identical functions centred at the resonant frequencies calculated in the absence of the quadrupolar nucleus.

ISSN:0026-8976    

DOI:10.1080/00268977000101131

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The effect of fluorosubstitution on the π-electron energy levels of benzene has been explained in terms of a two-parameter inductive model. One parameter is associated with a long-range perturbation which depends on the electric field of the C-F dipole moment, the other is associated with a short-range perturbation which depends on this field together with an exchange energy arising from the fluorine lone-pair electrons. The two parameters are calculated from the first IP of the fluorobenzenes and are then used to predict the shift in the second π IP and theu.v.(2600å) band of benzene on fluorosubstitution. There is good agreement between the calculated and observed results, and it is concluded that the second π IP of benzene is at 12·0 ev.

ISSN:0026-8976    

DOI:10.1080/00268977000101141

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Relaxation times,T1andT2, of deuterium in C6D6dissolved in the nematic phase of 4,4′-n-hexyloxyazoxybenzene at 75·3°c are reported. Relaxation times were calculated in terms of a correlation time τcusing the Redfield theory adapted for a partially ordered molecule. Values of τcderived fromT1andT2are similar.

ISSN:0026-8976    

DOI:10.1080/00268977000101151

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Calculations of lattice properties of argon, krypton and nitrogen are reported. For the rare gas crystals the aim has been to use a procedure that could reasonably be extended to more complicated molecular crystals. A pair potential of the Kihara type is used with constants deduced from gas phase measurements. A range of thermodynamic properties is calculated and compared with experiment. For crystalline nitrogen a preliminary investigation shows that an atom-atom interaction may be made the basis of a suitable potential function. Results for two specific forms of this type are given: in one, atom-atom potentials of the Lennard-Jones form are used and in the second a simple point charge distribution consistent with the measured quadrupole moment is added. Comparison is made with experimental infra-red and Raman frequencies.

ISSN:0026-8976    

DOI:10.1080/00268977000101161

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The equations which describe scattering of electrons by polar molecules are discussed. The criterion for the existence of a critical dipole moment which can bind an electron is introduced. The critical moments for a freely rotating dipole are shown to coincide with those already known for a fixed dipole, and a level-crossing scheme is developed. Finally the existence of well-behaved scattering solutions, corresponding physically to virtual inelastic transitions, even at supercritical moments, is demonstrated.

ISSN:0026-8976    

DOI:10.1080/00268977000101171

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The absolute displacements of the proton resonance signal for each of a number of non-polar molecules on going from gas phase to infinite dilution in a series of solvents, have been measured. An earlier conclusion relating the magnitude of the van der Waals shift to the degree of ‘solute proton exposure’ has been confirmed by employing the symmetrically substituted methylbenzenes as solutes. A significant intermolecular magnetic field is experienced by any solute dissolved in tetranitromethane even though the molecular properties of the latter are isotropic. Conversely, the highly anisotropic CS2molecule appears to produce an insignificant intermolecular magnetic field acting on any solute dissolved in carbon disulphide. Cyclohexane and cyclopentane only exert van der Waals forces on non-polar solutes and there is no effect on the solvent shift of their magnetic anisotropy, in sharp contrast to the case of non-polar solutes dissolved in benzene. The existence of weak hydrogen bonding between the hydrogen atoms of the methyl groups in dimethylacetylene and toluene and the oxygen atoms of alkoxy groups, underlines the sensitivity of proton chemical shifts to very weak specific interactions.

ISSN:0026-8976    

DOI:10.1080/00268977000101181

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

We have measured the anisotropic component of infra-red Rayleigh light scattered by some liquid alkanes and three aromatic compounds (benzene, naphthalene and azulene). There is an important dispersion in the anisotropy of benzene. The anisotropy of azulene and naphthalene are found to be of similar magnitude.

ISSN:0026-8976    

DOI:10.1080/00268977000101201

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Previous indications that the solvent-induced chemical shifts of the P.M.R. spectrum of pyridine were dominated by reaction field effects have been tested on a quantitative basis. The results show that, while this is indeed the case, the assumption that the reaction field is homogeneous over the dimensions of the solute molecule is a poor approximation in this instance.

ISSN:0026-8976    

DOI:10.1080/00268977000101211

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The electron resonance spectra of some fluorobenzyl radicals and fluorobenzaldehyde radical anions are reported. The observed hyperfine coupling constants are discussed in terms of π-electron spin densities estimated from semi-empirical molecular orbital calculations. Only one isomer is observed in the spectrum of theo-fluorobenzaldehyde radical anion, whereas two isomers are observed in the meta compound.

ISSN:0026-8976    

DOI:10.1080/00268977000101221

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor