The enhancement of enantioselectivity by halogen substituents

Abstract

For amide derivatives of 1-phenyl-1-ethylamines and for diethyl 1-(N-3,5-dimethylphenyl)amino-1-phenylmethanephosphonates with halogen substituents in the meta or para position of the benzenoid ring, increased retention and enantioselectivity are noted relative to their nonhalogenated counterparts. This is unexpected on the basis of prior observations that halogen substituents on benzenoid rings presumably undergoing face to face π-π interactions show reduced retention and enantioselectivity. These observations raise questions concerning the effect of polarizable electron-withdrawing substituents on the π-basicity of benzenoid systems.