[Explanation of C=O of acetone changing in solvents by some models].

Abstract

Raman spectra of acetone's carbonyl stretching in 16 solvents were measured, and were also calculated by self-consistent reaction field (SCRF) method in Gaussian03. The frequency shift in experiment was analyzed by donor-acceptor model, Kirkwood model and SCRF model respectively. Among them, the donor-acceptor model can explain the shift very well. The SCRF method can do it also, while not as well as the donor-acceptor model, but is better than Kirkwood model. Correlating the mechanisms of the 3 methods, it was found that the donor-acceptor model is powerful in explaining the vibrational spectra of molecular bond, which is nucleophilic reagent. The SCRF model considers not only the influence of dielectric constant epsilon, but also the influence of the bulk and the structure of molecule etc. Although the model is complex and difficult to calculate, but it takes many factors into account, so the calculated results accord with experiment better than the Kirkwood model. The main parameter of the Kirkwood model is epsilon, so it is very simple and easy to calculate, nonetheless the trend of frequency shift can still be reflected, indicating that the dielectric constant epsilon is a main character affecting the frequency shift.