Solvent Effects on the Barrier to C−N Bond Rotation in N,N-Dimethylaminoacrylonitrile: Modeling by Reaction Field Theory and by Monte Carlo Simulations

Abstract

Solvents are known experimentally to influence strongly the barrier to rotation about the conjugated C−N bond of N,N-dimethylaminoacrylonitrile (DMAAN). The barrier increases with overall solvent polarity, but solvent hydrogen-bond donor ability does not have a measurable effect. Two solvation models were explored in an attempt to reproduce the experimental data and obtain insight into the causes of the observed solvent effects. Calculations based on the isodensity polarizable continuum model (IPCM) encoded in Gaussian 94, a representative dielectric continuum-based procedure, yielded fair agreement for aprotic, nonhalogenated, nonaromatic solvents. The model predicts a linear correlation with the Onsager dielectric function, (e − 1)/(2e + 1), which was observed experimentally for this set of solvents. However, the model underestimated the magnitude of the solvent dependence by approximately 30%. As a representative example of an approach based on the use of explicit solvent molecules, Monte Carlo simulat...