The substituent effects on the 13c chemical shifts of the azomethine carbon atom of n-(phenyl substituted) salycilaldimines

Abstract

The Hammett correlations between 13C-NMR chemical shifts of the azomethine carbon atom and the corresponding substituent constants for thirtheen Schiff bases were established. Successful correlation of the chemical shifts with electrophilic substituent constants ?+ indicate significant resonance interaction of the substituents on the aniline ring with the azomethine carbon atom in the examined series of imines. The demand for electrons in the investigated compounds was compared to that of the N-benzylidenanilines and N-(phenyl substituted) pyridinealdimines. The way of transmission of the substituent effects was discussed and they are separated into resonance and inductive effects. Inductive effects prevail over resonance effects.