摘要:

The total lattice energy of benzene is evaluated by summation of pair interactions in the crystal. The relative contributions of the σ and π electrons to the attractive part of the energy are separated out explicitly: the π electrons contribute 40 per cent of this energy (although they represent only 20 per cent of the valence electrons). However the three component σ-σ, σ-π, and π-π dispersion energies are of the same order of magnitude. The effect of σ-π and π-π electron correlation is also investigated. The total lattice energy agrees well with the available experimental heat of sublimation data.

ISSN:0026-8976    

DOI:10.1080/00268976600101241

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The rate equations describing spin polarization in a system of three spins are derived and solved for the case of a free radical dissolved in a solvent containing two nuclear spins. Triple irradiation experiments indicate that a nuclear spin A can be effectively coupled to an electron spin C via a second nuclear spin B and measurements of both the steady state and transient Overhauser effects are in accord with the theoretical predictions for a three-spin system. The ‘three spin effect’ is found to operate only in dilute solutions of free radicals in which case the probabilities for transitions between different nuclear or electronic energy levels can be determined. It was found to be effective for fluorine nuclei—in the presence of both protons and a free radical and for carbon [13] nuclei in the presence of either protons or fluorine nuclei and a free radical. Detailed measurements have been performed for CHFCl2, para-difluorobenzene, and meta-fluorotoluene containing the tritertiary butyl phenoxyl radical.

ISSN:0026-8976    

DOI:10.1080/00268976600101251

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The magnitudes of the contributions to the magnetic shielding constant of a fluorine nucleus are discussed which are important when chemical shifts are obtained by recording the spectra of liquid samples. The chemical shifts between CFCl3, C6F12, C6F4Cl2and C6F6in various solvents have been measured, and it is concluded that an internal reference compound for fluorine should be of the same chemical type, and similar in size and shape to the molecules under investigation. The variations with solvent of the chemical shifts measured relative to C6F6as an internal reference of the polar molecules pentafluoropyridine, 4-nitrotetrafluoropyridine, pentafluorobenzene, chloropentafluorobenzene and nitropentafluorobenzene have been measured and discussed in terms of the reaction fields produced by interaction of the polar molecules with the surrounding medium. The results have been shown to be consistent with the equationδ= -AEz, and values of the constantAhave been obtained. The data of Taftet al.[7–9] on the effect of solvents on the chemical shifts of19F nuclei inparaandmetasubstituted fluorobenzenes relative to fluorobenzene has been re-examined and interpreted as arising predominantly from the reaction fields produced. It is concluded that only in the case of the fluoropyridines as solutes and alkylbenzenes as solvents is their evidence of the effect of complex formation on fluorine chemical shifts.

ISSN:0026-8976    

DOI:10.1080/00268976600101261

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The interaction of a molecule with a quantized electromagnetic field is described within the framework of formal scattering theory. It is shown that the probability of multiphoton molecular transitions may then be represented in a particularly simple way by diagrams. Rules for constructing and interpreting these diagrams are described. Two forms of interaction potential are employed, namely, the standard form of non-relativistic limit of the Dirac equation, and an alternative formulation due to Richards [12]. The advantages of the alternative form are shown to be that terms which are bilinear in the field may be neglected, and that the remaining terms represent the multipole moment interactions of the molecule with the quantized field.

ISSN:0026-8976    

DOI:10.1080/00268976600101271

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

A calculation of the energies of the dipolar and quadrupolar electric fields of a 1,2-disubstituted ethane and their dependence on the dielectric constant of the medium gave results in good agreement with experiment for the energy differences between the rotational isomers in the gas and liquid phases. The theory is used to derive the proton-proton and proton-fluorine coupling constants of the rotational isomers of 1-chloro-2-bromo, 1-chloro-2-fluoro and 1-bromo-2-fluoro ethane from the solvent dependence of the proton resonance spectra. Notable deviations from this classical theory are found with aromatic solvents and are due to specific interactions of the solvents with the more polar rotational isomer.

ISSN:0026-8976    

DOI:10.1080/00268976600101281

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

The crystal and molecular structure of B-trimethylborazole has been established. By two-dimensional methods a structure model could be derived which was subsequently subjected to three-dimensional refinement. This refinement gave the expected shape of the molecule with good accuracy.

ISSN:0026-8976    

DOI:10.1080/00268976600101291

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268976600101301

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268976600101321

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor