A third type of alkylamines possessing high nitrogen inversion–rotation barriers

A new type of alkylamines possessing high nitrogen inversion–rotation (NIR) barriers is described (in general, these are hindered cyclic amines). The increase in barrier values for these amines is caused by an increase in steric interactions in the NIR transition state due to restrictions for N-substituent rotation (usually steric repulsion of N-substituents is decreased on going to a planar NIR transition state of alkylamines). Since these compounds may be essentially different in structure, a comparison between the NIR barriers of homologs is proposed as a criterion for the assignment of amines to this type. According to this criterion, the NIR barriers are drastically increased (3–5 kcal mol⁻¹) on going from NMe or NH (usual amines) to more bulky N-alkylhomologs (amines of the third type). Structures of some of these amines were predicted and their NIR barriers were estimated by MM3. Copyright © 1999 John Wiley & Sons, Ltd.