Hydrogen bonding and long-range proton coupling constants in some ortho disubstituted aniline derivatives. Intramolecular proton exchange and degree of nonplanarity of the amino group

Abstract

Long-range spin–spin coupling constants over five bonds between the two amino protons and the ring protons are reported for some ortho disubstituted aniline derivatives in cyclohexane and benzene-d6 solutions. Equal coupling of both amino protons to the meta protons in unsymmetrically ortho disubstituted aniline derivatives indicates the occurrence of intramolecular exchange of the amino protons. The absence of any observable coupling over six bonds to the para proton places an upper limit on the degree of nonplanarity of the amino group in the 2,6-dibromo- and 2,6-dichloroanilines. A relatively basic compound like 2,4,6-trimethylaniline does not display long-range couplings of the amino protons, very likely because intermolecular proton exchange occurs.