CORRELATION-ANALYSIS OF THE C-13 CHEMICAL-SHIFTS OF SUBSTITUTED BENZALDEHYDE 2-AMINOBENZOYLHYDRAZONES - STUDY OF THE PROPAGATION OF SUBSTITUENT EFFECTS ALONG A HETEROATOMIC CHAIN

The C-13 chemical shifts of eight series of para- or meta-substituted benzaldehyde 2-aminobenzoylhydrazones possessing both amide and imine functionalities were measured. The C-13 chemical shifts were used to s tudy the transmission of electronic substituent effects along the hete roaromatic side-chain of the substituted aromatic ring, In addition to the C=N bond, the benzoylhydrazones possess in their side-chain polar izable C=O and phenyl pi-units. The benzylidenic ring-substituent chem ical shifts were analysed by the dual substituent parameter approach t o separate the inductive and resonance effects, The negative p(I) and p(R) values observed (i.e. reverse substituent effects) indicate a sig nificant pi-polarization of the C=N bond, The highly negative p(R) val ues, especially those in the case of meta substitution, suggest a cont ribution from a marked secondary field-transmitted resonance effect, T he results are compared with those obtained for other hydrazones or im ines. Variation of the electron-withdrawing ability of the N-2 substit uent is seen to have a systematic effect on the p(I) values. Reverse s ubstituent effects are also observed at the C-1'' site of the 2-aminob enzoyl ring while C-4'' shifts show normal behaviour, consistent with the general concept of the pi-polarization that each pi-unit of the si de-chain is polarized largely as a localized system, Accordingly, the pi-polarization effect is seen efficiently to propagate also along a h eteroaromatic chain, On the other hand, the C=O sites exhibit normal, although fairly slight, dependence on the benzylidenic substituent ind icating an insignificant role of pi-polarization at that site. The eff ects of the solvent, CDCI3 vs. DMSO-d(6), on the p(I) and p(R) values are also considered.