FT-IR Experiments With Gaussian Calculation Of Solvent Effects Of Vinyl Acetate

Theoretical and experimental results of solvent effects not only provide rationales for the inquiry on the chemical reaction mechanisms, spectroscopic properties and biochemical aspects, but also have practical significance for the reaction solvent screening and the optimization of reaction conditions. Therefore, Researches on the solvent effects have always been popular in the field of chemistry. This study centered on the solvent effects of polymerization of VAc with the combination of FT-IR experiments and Gaussian calculation.The regualar pattern of solvent-induced shift of carbonyl vibration frequency (vexp(C=O)) for vinyl acetate (VAc) in12different nonalcohol solvents and6different alcohol solvents were investigated by FT-IR spectroscopy. The carbonyl vibration frequency (vcal(C=O)) and solvation free energies (AG) of VAc in18different solvents were calculated at the level of DFT B3LYP/6-311G*by PCM model and SMD model, respectively, and the relationship between the vcal(C=O) and reactivity of C=C was explored.4different single-parameter solvent equations and2different multi-parameter solvent equations were correlated with the vexp(C=O) and vcal(C=O). The fact that the vcal(C=O) behaved unsatisfying correlation with all the parameters but the KBM parameter indicated the PCM model can describe dielectric-constant-induced solvent effects but it fails to comprehensively reflect solute-solvent interactions. The correlation between the vexp(C=O) and the G was the best, and the next was the one with the AN, the correlation between the vexp(C=O) and Et(30) or KBM were relatively poor. Although the parameters of AN, ET(30), KBM, G reflect solvent effects to some extent, they do not reflect the nature of solute-solvent interactions. The vexp(C=O) achieved good correlations with the parameters of Swain and LSER equations.The advantage of LSER equation is that it offers a quantitatively accurate and physically meaningful explanation of solvent-induced stretching frequency shifts. Different kinds of hydrogen bond between VAc and alcohol were investigated by ab initio calculation using DFT B3LYP/6-311G*. The Band I belongs to C=O building H-bond with solvent in different modes including1:1H-bond and1:2H-bond. The Band II corresponds to non-specific VAc-solvent interactions.The solution polymerization of VAc was monitored by FT-IR experiments. The changes of infrared absorption peaks of VAc during the reactions of different systems were observed in order to probe into solvent effects on the reaction rate and conversion degree of polymerization of VAc. The studies showed that the conversion degree in methanol solvent system was higher than that in hexane and dichloromethane.Therefore, the solvent-induced carbonyl frequencies can be used to infer the reaction activities of VAc, thus providing the basis for choosing the solvent of reaction.