J. Phys. Chem. 1994, 98, 4842-4844
4842
The Polarizability of Some Deuterated Hydrocarbons D. G . LeGrand' General Electric Research and Development Center, Schenectady, New York 12301
G. L. Caines, Jr. Chemistry Department, Rensselaer Polytechnic Institute, Troy, New York 12180-3590 Received: March 9, 1994"
The refractive indices of perdeuterated hydrocarbons n-hexane-dlr, heptane-d16, and octane-dl8, benzene-da, toluene-d8, and ethylbenzene-dlo have been measured a t room temperature at five different wavelengths. The polarizabilities of these compounds have been computed as a function of wavelength using the Lorentz-Lorenz equation and a t infinite wavelength using the Cauchy equation. In all cases, the polarizabilities of the deuterated compounds are less than the corresponding nondeuterated compounds.
Refractive indices of perdeuterated and protonated hexane as function of wavelength.
Introduction The effects of molecular weight and end groups on the surface and interfacial tension of low molecular weight oligomeric hydrocarbons and on polymers have been reported by a number of investigators.'" More recently, the effects of deuteration on the mixing and surface activity of isotopic polymers and the surface tension of low molecular weight hydrocarbons have been discussed.7-9 It has been argued that the nonideality of mixing and the surface activity in isotopic blends are a consequence of differences in the Flory-Huggins's x parameter.' This difference in the segment-segment interaction has been attributed to differences in the segmental volume and thevan der Waals forces between the deuterated and protonated polymer liquids. In the case of the van der Waals forces, this term has been estimated by the use of the London formula and from the difference in the segment polarizabilities on the basis of the work of Bell.Io A careful examination of Bell's work indicates that the polarizabilities were computed from data on substances in the gaseous state. In view of this circumstance, it seemed appropriate to determine the polarizabilities of a series of simple hydrocarbons in the liquid state and to compare them to those computed from the work of Bell. Although this comparison was the primary objective of the work, it was also of interest to determine if the same simple correlation between surface tension and molecular weight existed for the perdeuterated alkanes as for protonated alkanes and if empirical equations such as the parachor or the MacLeod equation could be used to predict the surface tension of deuterated hydrocarbons on the basis of nondeuterated materials.
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