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Correlation analysis of the 13 C chemical shifts of substituted benzaldehyde 2‐aminobenzoylhydrazones. Study of the propagation of substituent effects along a heteroatomic chain
Author(s) -
Neuvonen Kari,
Fülöp Ferenc,
Neuvonen Helmi,
Simeonov Mario,
Pihlaja Kalevi
Publication year - 1997
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199701)10:1<55::aid-poc854>3.0.co;2-d
Subject(s) - substituent , chemistry , chemical shift , amide , benzaldehyde , imine , side chain , ring (chemistry) , polarizability , computational chemistry , stereochemistry , crystallography , organic chemistry , molecule , polymer , catalysis
The 13 C chemical shifts of eight series of para ‐ or meta ‐substituted benzaldehyde 2‐aminobenzoylhydrazones possessing both amide and imine functionalities were measured. The 13 C 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 CN bond, the benzoylhydrazones possess in their side‐chain polarizable CO 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 ρ I and ρ R values observed ( i.e. reverse substituent effects) indicate a significant π‐polarization of the CN bond. The highly negative ρ R 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 N 2 substituent is seen to have a systematic effect on the ρ I 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 CO 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, CDCl 3 vs. DMSO‐ d 6 , on the ρ I and ρ R values are also considered. © 1997 John Wiley & Sons, Ltd.