Chirale Butadiene 6. Behinderte Rotation an penta- und hexasubstituierten Butadienen – Stützeffekte

Abstract

A series of hexasubstituted butadienes of type A was prepared representing (E,E)-1,2,3,4-tetrachloro-5-methoxy-1,3-pentadienes (7) substituted by different terminal residues R. 1H n.m.r. data of diastereotopic methylene protons served to determine the barriers of rotation around the central CC single bond of the butadienes A. The considerable dependence of this barrier (ΔGmath image = 12.8–21.1 kcal/mole) upon the size of the terminal substituents R ist discussed in terms of a buttressing effect of these groups.