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Electronic effects of heterocyclic ring systems as evaluated with the aid of 13 C and 15 N NMR chemical shifts and NBO analysis
Author(s) -
Neuvonen H.,
Fülöp F.,
Neuvonen K.,
Koch A.,
Kleinpeter E.
Publication year - 2008
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/poc.1271
Subject(s) - chemistry , natural bond orbital , substituent , electronegativity , hydrazone , thiophene , chemical shift , heteroatom , carbon 13 nmr , pyridine , furan , imidazole , polar effect , computational chemistry , medicinal chemistry , stereochemistry , ring (chemistry) , density functional theory , organic chemistry
The electronic effects of the 5‐ and 6‐membered heterocyclic rings on the CNN unit of five different hydrazone derivatives of pyridine‐2‐, ‐3‐ and ‐4‐carbaldehydes, pyrrole‐2‐carbaldehyde, furan‐2‐ and ‐3‐carbaldehydes and thiophene‐2‐ and ‐3‐carbaldehydes have been studied with the aid of 13 C and 15 N NMR measurements together with the natural bond orbital (NBO) analysis. As model compounds are used the corresponding substituted benzaldehyde derivatives. The polarization of the CN unit of the hydrazone functionality of the heteroaryl derivatives occurs in an analogous manner with that of phenyl derivatives. The electron‐withdrawing heteroaryl groups destabilize and the electron‐donating groups stabilize the positive charge development at the CN carbon while the effect on the negative charge development is opposite. The 15 N NMR chemical shift of the C N and CN N nitrogens and the NBO charges at CNN unit can be correlated with the replacement substituent constants σ of the heteroaryl groups. 13 C NMR shifts of the CN carbon of N , N ‐dialkylhydrazones of the heteroarenecarbaldehydes can be correlated with a dual parameter equation possessing the polar substituent constant σ * of the heteroaryl group and the electronegativity of the heteroatom as variables. Copyright © 2008 John Wiley & Sons, Ltd.