Computational (solute-solvent cluster + PCM) study of medium effects on the experimental 13C and 1H NMR chemical shifts of lactones and lactams

Abstract

Solvent effects on the 1H and 13C NMR chemical shifts of some lactones: β-propiolactone, γ-butyrolactone, δ-valerolactone and ε-caprolactone, as well as lactams: azetidin-2-one, pyrrolidin-2-one, δ-valerolactam and ε-caprolactam have been investigated and discussed in a wide range of solvents. The experimental results were compared with density functional calculations using a large basis set. Solvent effects were computed by means of an integrated approach including the polarizable continuum model and an optimum number of explicit solvent molecules surrounding the solute. The agreement between computed and experimental chemical shifts fully validates our integrated approach. In order to quantify and elucidate the origin of the solvent effects on the 1H and 13C chemical shifts of the selected compounds, a multi-linear regression analysis has been carried out using the empirical Kamlet–Abboud–Taft solvatochromic parameters. It has been found that there is a good correlation between the solvent-induced chemical shifts of 13C and the π* scale of solvent dipolarity polarizability. 1H chemical shifts are affected mainly by the dipolarity–polarizability and the basicity of the solvent. An excellent agreement has been obtained between the calculated and the experimental data. Copyright © 2011 John Wiley & Sons, Ltd.