Kerr effect studies of the conformations of mono- and di-carboxylic aliphatic esters

Abstract

The dipole moments and molar Kerr constants of dimethyl and diethyl malonate in carbon tetrachloride at 25°C are recorded. Details of the equipment and procedures are given. A re-examination of polarity and polarizability of –CO₂Me group and the C(sp₂)–O bond indicates that the CO₂Me group is planar. The CNDO/2 method has been used to deduce the preferred gas-phase conformations of dimethyl malonate. The preferred solution-state conformations of dimethyl and diethyl malonate, indicated by the analysis of experimental and calculated dipole moments and by molar Kerr constants, are shown to be consistent with the theoretical predictions. The experimental data for the investigated dicarboxylic esters may be well interpreted in terms of two rotamer populations centred on two energy minima separated by a barrier of 2–3 kcal mol^–1(τ₁= 90°; τ₂= 90°, and τ₁= 90°; τ₂= 270°).