S. Masuda et al., INFRARED INTENSITIES OF THE C=C AND C=N STRETCHING MODES OF CONJUGATED SCHIFF-BASES - A STUDY BASED ON AB-INITIO MOLECULAR-ORBITAL CALCULATIONS, Journal of physical chemistry, 100(38), 1996, pp. 15335-15339
Vibrational analyses of model compounds of protonated and unprotonated
conjugated Schiff bases are performed by use of force fields derived
from ab initio molecular orbital calculations. The calculated force fi
elds and dipole derivatives correctly reproduce the observed infrared
frequencies and intensities of the C=C and C=N stretching bands. The o
rigin of the infrared intensities of these bands is examined in detail
in terms of the magnitudes and directions of dipole derivatives. It i
s shown that a normal mode having a large contribution of the in-phase
skeletal stretching coordinate gives rise to a strong infrared absorp
tion. The strong infrared intensity is explained by a large change in
the electronic structure that causes charge flux in the molecular skel
eton.