Aromatic imine stereochemistry as studied by 13C and 1H NMR of 15N-enriched materials

A series of thirteen ¹⁵N-enriched N-aryl imines derived from benzaldehydes and acetophenones have been prepared and examined by ¹³C and ¹H NMR. Preferred conformations of the C-arvl and N-aryl rings have been deduced from ¹³C chemical shifts and ¹³C-¹⁵N couplings. Evidence for steric inhibition of resonance in O-alkylated materials is presented. Relative signs of ¹J(CN) and ²J(CCN) have been determined in some compounds. An E: Z interconversion barrier of 21.6 kcal mol^?1 has been obtained from ¹H NMR coalescence data.