Molecular polarisability. The dipole moments and molar Kerr constants of 1,3- and 1,4-diacetylbenzenes and their polymethylated derivatives

Abstract

Dipole moments and molar Kerr constants (× 10¹²) at 25° are recorded for 1,4-diacetylbenzene (3·03 D, +64·0), 1,3-diacetylbenzene (3·19 D, +380), 1,4-diacetyl-2,3,5,6-tetramethylbenzene (2·99 D, –530), and 1,3-diacetyl 2,4,6-trimethylbenzene (3·15 D, –346) as solutes in carbon tetrachloride. New measurements of the molar Kerr constants of 1,3,5-trimethylbenzene and 1-acetyl-2,4,6-trimethylbenzene are reported. Results for 1,4- and 1,3-diacetylbenzene are compatible with equilibrium mixtures of planar or near-planar cis- and trans-rotamers, while those for the strongly hindered methyl-substituted derivatives are interpreted in terms of orthogonal cis- and trans-conformations.