Principle of additivity of dipole moments: Halogen derivatives of adamantane

Abstract

Dipole moments of halogenated adamantanes II-IV were measured in two solvents using the Guggenheim-Smith method. The reliability of the method was checked on non-polar symmetrical compounds I, V. The dipole moments of 1,3-dihalogen and 1,3,5-trihalogen derivatives reveal small but real deviations from the additive behaviour: the experimental values are less than those calculated by vector addition from the moments of monoderivatives, assuming tetrahedral geometry. This fact can be explained by mutual induction of dipole rather than by angle deformation, although both effects can contribute. The deviations from the additive behaviour are qualitatively represented by CNDO/2 calculations with fixed geometry. However, even the greatest deviations observed amount only several percent in relative values and do not impair the general applicability of the bond moment approach.