摘要:

An analysis of the NMR spectra of I, I-difluoroethylene and tetrafluoroethylene in a nematic solvent is given. The results are compared with previous findings on ethylene itself. The geometrical structures of the fluorine substituted molecules, as determined from NMR data neglecting the anisotropy of the electron coupled spin-spin interaction, deviate considerably from structural data obtained by other methods. It is concluded that there is a strong anisotropy in the electron coupled interactions between the19Fnuclei.

ISSN:0369-1152    

DOI:10.1080/15421407008083467

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Photoeletron emission from various aromatic hydrocarbon crystals has been studied and some of the factors (space charge, sample preparation) which might influence the phtoelectric threshold have been investigated. The longstanding problem of determining the “true” photoelectric threshold is re-examined, and a semi-empirical expression is derived which adequately accounts for the spectral dependence of the photoelectron emission yield, and at the same time determines the threshold. New photoelectric thresholds for a number of anthracene derivatives are also reported.

ISSN:0369-1152    

DOI:10.1080/15421407008083468

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Cycloartenyl palmitate has been isolated from banana peel (Mus sapientum) and from the seeds ofStrychnos nux-vomica. This ester forms a cholesteric mesophase. The ester was carefully purified from each of these sources and identified by comparison of chemical, physical and mass spectral properties with an authentic sample of cycloartenyl palmitate. The isolation of this cholesteric ester is of interest since such substances have not been reported in plants and have been found only rarely in animal tissue

ISSN:0369-1152    

DOI:10.1080/15421407008083469

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Since a thermally induced helical inversion has been observed in cholesteryl 2-(2 ethoxyethoxy) ethyl carbonate (CEC), it has been the view that compensation of the helical structure of cholesteric liquid crystals does not require the presence of two compounds which separately form a right and a left handed helix. The present investigation demonstrates that the material used in the previous investigation was probably a compensated mixture because it contained an impurity in a rather high concentration. Pure CEC forms a right handed helix with a pitch of 6000 Å at room temperature, and with no indication of a thermally induced helical inversion. It is further shown that in general the sense of the helical screw is not necessarily identical with the sign of the optical rotation of the constituent molecules.

ISSN:0369-1152    

DOI:10.1080/15421407008083470

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

The lattic energy (U) of naphthalene and anthracene crystals as a function of the unit cell volume (v) has been calculated by the atomatom potential method. The experimental thermal expansion tensor has been used in this calculation. The first and the second derivatives of the lattice energy with respect to the unit cell volume have been obotained from the curveU(v>. Methods of comparison of these values with experimental data on the crystal internal energy and its volum, e derivatives and also ways of calculating the vibrational part of the crystal internal energy have been discussed. It has been shown that vibrational corrections to the lattice energy and its volume derivatives are small.

ISSN:0369-1152    

DOI:10.1080/15421407008083471

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Experiments are reported on the production, and annealing kinetics of free radicals in irradiated organic crystals. Both processes are shown to be well reproducible for nominally identical crystals although the annealing rate may be much slower in crystals damaged by previous irradiation and annealing. Free radical destruction was found in numerous instances to proceed by second-order kinetics, the only exception being crystals of acetylglycine where the reaction is third-order. Activation energies of the reactions are reported together with experimental investigation of the deuterium isotope effect. The significance of these results is discussed in relation to the existence of hydrogen atom jumping of “Kenon diffusion” as and annealing mechanism.

ISSN:0369-1152    

DOI:10.1080/15421407008083472

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Heretofore, ethanol has been the most widely used solvent for the recrystallization of cholesteryl esters. In this study of some solubility characteristics of cholestery1 esters,n-pentanol is shown to be a more effective solvent than ethanol in which to remove impurities and/or crystalline structural defects from cholesteryl esters that can cause additional transitions on initial heating.n-Pentanol is shown to be a regular solvent for cholestetryl esters, whereas ethanol is not. This could be a major reason whyn-pentanol is better able to discriminate between compound and impurity than ethanol. Contrary to previous reports, after crystallization fromn-pentanol, in contrast to ethanol, cholesteryl acetate and cholesteryl laurate have only one transition on first heating. A detailed study of cholesteryl benzoate recrystallized fromn-pentanol has confirmed that there are two transitions, one at 146.0 °C. the secpond at 179.6 °C. The heats of transitions are found to be 14.7 cal./gm. and 0.26 cal./gm. respectively.

ISSN:0369-1152    

DOI:10.1080/15421407008083473

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

A combined Fermi-Davydov resonance in solid molecular solutions is considered. It is shown that migration of the energy of vibrational excitation can lead to an abnormal redistribution of intensities of the components of Fermi-doublet when higher order harmonics are dominant. The concentrational dependence of the ratio of the intensities of doublet components is investigated. At a certain value of the concentration, determined by parameters of the solvent and the dissolved substance, a sharp increase in the intensity of one of the doublet components can be observed. The basic conclusions of the theory are in agreement with the experiment.

ISSN:0369-1152    

DOI:10.1080/15421407008083474

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

The proton magnetic resonance absorption inn-butyl stearate has been investigated for the range −196° to 24 °C. The second moment data are discussed and the amplitudes of molecular rotations at different temperatures are calculated.

ISSN:0369-1152    

DOI:10.1080/15421407008083475

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

In a preivous publication1we reported on the photoconductivity of polystyrene for excitation in the vacuum ultraviolet. The threshold for the onset of this photoelectric effect was interpreted as indicating that photon energies which are close to the ionization energy of the free molecules (in this case, benzene) were necessary for the process to occur. In order to investigate whether this requirement holds in general we investigated the effect for a variety of other organic solids; polyuethylene, anthracene, naphthalene, paraffin wax (m.p. 48 °C and m.p. 52 °C), cellulose and glucose. The results are shown in Fig. I Which describes the variation of the photocurrent with excitation wavelength for the various materials. The curves have been normalized to the value 100 for excitation at 584 Å. The intensity of the exciting radiation was normalized by the fluroescence of sodium salicylate. It shall be pointed out that in order to obtain comparative current intensities the applied voltage for cellulose was 10 Volt, for glucose 1 Volt, while the necessary voltage for the other matrerials varied between 200–300 Volts. At 200 Volts, the dark current for glucose and cellulose was already greater than the photocurrent.

ISSN:0369-1152    

DOI:10.1080/15421407008083476

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor