ISSN:
0894-3230
Keywords:
Chemistry
;
Theoretical, Physical and Computational Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The 13C chemical shifts of eight series of para- or meta-substituted benzaldehyde 2-aminobenzoylhydrazones possessing both amide and imine functionalities were measured. The 13C chemical shifts were used to study the transmission of electronic substituent effects along the heteroaromatic side-chain of the substituted aromatic ring. In addition to the C=N bond, the benzoylhydrazones possess in their side-chain polarizable C=O and phenyl π-units. The benzylidenic ring-substituent chemical shifts were analysed by the dual substituent parameter approach to separate the inductive and resonance effects. The negative ρI and ρR values observed (i.e. reverse substituent effects) indicate a significant π-polarization of the C=N bond. The highly negative ρR values, especially those in the case of meta substitution, suggest a contribution from a marked secondary field-transmitted resonance effect. The results are compared with those obtained for other hydrazones or imines. Variation of the electron-withdrawing ability of the N2 substituent is seen to have a systematic effect on the ρI values. Reverse substituent effects are also observed at the C-1″ site of the 2-aminobenzoyl ring while C-4″ shifts show normal behaviour, consistent with the general concept of the π-polarization that each π-unit of the side-chain is polarized largely as a localized system. Accordingly, the π-polarization effect is seen efficiently to propagate also along a heteroaromatic chain. On the other hand, the C=O sites exhibit normal, although fairly slight, dependence on the benzylidenic substituent indicating an insignificant role of π-polarization at that site. The effects of the solvent, CDCl3 vs. DMSO-d6, on the ρI and ρR values are also considered. © 1997 John Wiley & Sons, Ltd.
Additional Material:
14 Ill.
Type of Medium:
Electronic Resource
Permalink