1 4 N/ 1 5 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, 1 5 N- 1 H coupling constants and the 1 4 N 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 1 3 C 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.