Molecular polarisability. The anisotropic electron polarisability of aliphatic C–C and C–H bonds

Abstract

Previous determinations of the anisotropic polarisability of aliphatic C–C and C–H bonds are reviewed. Kerr-effect measurements of several alicyclic hydrocarbons in solution and as pure liquids are reported, and previous measurements are reconsidered. The parameter Γ_CC≡(b_L^CC–b_T^CC)–2(b_L^CH–b_T^CH) is evaluated from eight independent determinations in solution as 0·71 ± 0·3 ų, and from five determinations for liquids as 0·80 ± 0·15 ų, in good agreement with recent light-scattering results. Methods of obtaining C–C and C–H bond polarisabilities separately are discussed, and consideration given to the effect of small deviations from tetrahedral bond angles on the determinable polarisability parameters of aliphatic molecules. The conformation of the cyclooctane ring is investigated, but results are inconclusive.