DEUTERIUM-ISOTOPE EFFECTS AS EVIDENCE FOR SUBSTITUENT PERTURBATION OFTHE PI-ELECTRON FRAME IN BENZANILIDES

Deuterium isotope effects on C-13 nuclear shielding, (n) Delta C(D), t ransmitted across a D-labelled nitrogen atom were investigated for a s eries of para-substituted benzanilides. The two two-bond isotope shift s, (2) Delta C(D) are perturbed essentially in a trough-bond manner by change of the contribution of mesomeric structures. The magnitudes of (2) Delta(C=O) and (2) Delta(C-1') are found to be mutually interdepe ndent as evidenced by the linear relationships between the average val ues of (2) Delta(C=O) and (2) Delta(C-1') with H-1(NH) chemical shifts and with N-15 SCS. This behaviour is interpreted as resulting from a cross-conjugated transmission pathway involving the carbons sharing th e D-labelled nitrogen.