ToBaD: A method for the estimation of torsion barriers from crystal structure data; conformational analysis of N,N-dimethylaniline and derivatives

A new method for the estimation of torsion barriers and its application to conformational analysis is presented. This method, the ToBaD method (method of the torsion barrier derivative), makes use of crystal structure data. It is based on the assumption that the conformation of a compound in the crystalline phase must be very close to a (local) minimum energy conformation of this compound in the gas phase. The ToBaD method is demonstrated for the rotation of the phenyl-N bond in N,N-dimethylaniline. Two geometries of this compound are handled separately: one in which the nitrogen substituents are in a pyramidal or sp³ geometry, and the other in which the nitrogen atom and its substituents are coplanar (the sp² geometry). It is predicted, by means of the ToBaD method, that for both geometries the conformation in which the nitrogen lone pair or p orbital is perpendicular to the aromatic ring is the lowest energy conformation. © 1994 by John Wiley & Sons, Inc.