ABSTRACT
The spectral and structural changes, caused by the conversion of the vanillin molecule into the corresponding oxyanion have been studied by IR spectra and normal coordinate calculations within the Onsager self-consistent reaction field (SCRF) model, using a density functional theory (DFT) method at the Becke3LYP/6-31+G** level. Structures of all conformational isomers of vanillin and of its anion have been located, as well as their total and relative energies have been determined. The conversion leads to geometry changes in the whole species, due to the strong O-/acceptor polar resonance through the para phenylene ring. The conversion causes a 41 cm(-1) decrease in the frequency of the carbonyl stretching band nu(C=O), strong intensity increases (1.6 - 7.2-fold) of the aromatic skeletal nu8 and nu19 as well as formyl nu(CH) bands. According to the calculations the oxyanionic charge is delocalized over aldehyde group (0.25 e-), phenylene ring (0.13 e-), methoxy group (0.07 e-) and oxyanyonic center (0.55 e-).
Subject(s)
Benzaldehydes/chemistry , Anions/chemistry , Molecular Structure , Spectrophotometry, Infrared , Stereoisomerism , ThermodynamicsABSTRACT
The spectral and structural changes, caused by the conversion of the 3-hydroxybenzaldehyde molecule into the corresponding oxyanion have been studied by IR spectra, and MP2 and DFT force field calculations. The conversion causes a 13 cm(-1) decrease in the frequency of the carbonyl stretching band nu(Cz=O), a 1.3-fold increase in its integrated intensity, strong intensity increases (2.1-5.3-fold) of the aromatic skeletal nu8 and nu19 as well as formyl nu(CH) bands. According to the calculations the oxyanionic charge is delocalized over aldehyde group (0.37 e-), phenylene ring (0.12 e-) and oxyanionic center (0.52 e-). The conversion into the oxyanion leads to geometry changes in the whole species, but it remains planar.
