A theoretical approach to experimental nitration of phenyl and benzyl substituted pyridine derivatives

Quantum chemical calculations of 2-, 3-, and 4-phenyl substituted pyridine derivatives reveal that 2-phenylpyridine nitrates via conjugated acid mechanism whereas 3- and 4-phenylpyridine molecules may nitrate via free base or more correctly an ipso attack to ring nitrogen atom followed by migration of nitronium ion to different positions of the phenyl ring to gain thermodynamic stability. Calculations for 2-, 3-, and 4-benzylpyridines revealed that all three compounds nitrate via the conjugated acid forms. Attempts to search correlations between the experimental acidity constants, pK(a), and computed acidity constants were successful. (C) 2003 Published by Elsevier Science B.V.