14N and 15N NMR studies of highly sterically hindered tertiary amines

Abstract

14 N 15 N NMR and molecular mechanics MM2 have been applied to study the structural changes in a series of highly sterically hindered amines. The NMR parameters, chemical shifts, 15N- 1H coupling constants and the 14N linewidths, are sensitive to the variations in sterical hindrance about the nitrogen. In particular, the chemical shift of the extremely hindered tri-isopropylamine ( 4) has been shown to deviate from the correlation calculated from the substitution parameters and from the correlation with the 13C chemical shift of the corresponding hydrocarbon. These results are consistent with the results of a gas phase electron diffraction study which showed that 4 exhibits a trigonal planar structure.