Dipole moments and conformation of some olefinic and ortho-substituted aromatic methoxy derivatives

Abstract

Dipole moments of stereoisomeric 3-methoxypropenenitriles (I,II), substituted 2-methoxybenzonitriles (III-VI) and substituted 2-chlorophenyl methyl ethers (VII-X) were measured in benzene solution and analyzed in terms of group moments. Aromatic derivatives III-X exist in the prevailing conformation ap (CH3 trans to Cl or to CN). Any minor conformation was not detected; small differences between experimental and calculated dipole moments were explained by induction of the two adjacent dipoles. Conformations of 3-methoxypropenenitriles were estimated to prevailing sp for I and practically only ap for II. Irrespective of the conformations, dipole moments revealed a strong conjugation of the CN and OCH3 groups in I and II. The intensity of this conjugation in various derivatives thus decreases steeply in the series: olefinic E > olefinic Z > aromatic para > aromatic ortho.