Conformational stability of 2,2 '-dialkoxybenzpinacols in solid state

X-ray analyses of the 2,2'-dialkoxybenzpinacols have established that the p reviously tentative assignment of configuration is incorrect. For ex-ample, the dl- and meso-isomer of 2,2'-dimethoxy-, 2,2'-diethoxy-, and 2,2'-dibut oxybenzyinacols proved to have a rigid conformation (1a alpha, 1b alpha, 1c alpha) and (1a beta, 1b beta, 1c beta) where hydroxy groups are always in an anti fashion, in the solid state, respettively. MM2 and semi-empirical m olecular orbital calculations for possible conformations were performed, su ggesting that the conformational stability of the present pinacols is contr olled by repulsive gauche interactions between aryl groups associated with intramolecular hydrogen bondings.