INFRARED STUDY OF 4-SUBSTITUTED BENZALDEHYDES IN DILUTE-SOLUTION IN VARIOUS SOLVENTS - THE CARBONYL STRETCHING MODE

The carbonyl stretching mode in some of the 4-x-benzaldehydes is in Fermi resonance with an overtone of a fundamental which occurs at lower frequency. In general, the unperturbed (nu)C = O frequencies for 4-x-benzaldehydes do appear to correlate with the sigma(p) values of the 4-x atom or group. The AN values of the solvents show a pseudo-correlation with the carbonyl and nu(asym).NO2 stretch vibrations of 4-x-benzaldehyde. However, neither sigma(p) nor AN values appear to take into account solute/solvent interactions such as intermolecular hydrogen bonding with the C = O group and with other sites in the molecule such as the phenyl group pi system and with the electronic system of other functional groups, since the points in each plot do not correlate in the exact manner in each case.