C-N rotational barriers in aromatically substituted styrylformamides: an AM1 study utilizing the conductor like screening model for real solvents

Semi-empirical calculations at the AM 1 level utilizing the Conductor Like Screening Model for Real Solvents (COSMO-RS) are performed on a series of styrylformamides in their E, Z and transition state conformations to determine barriers to rotation (BIR) about the amide bond. Comparison is made with experimental data from two-dimensional exchange correlation spectroscopy NMR experiments (2D EXSY). Equilibrium and transition state structures are analyzed to explain the observed decrease in rotational barriers with electron withdrawing substituents. Calculations of nonexperimentally determined structures are performed to predict rotational barriers. The theoretically observed trends correspond well with chemical intuition. (C) 2001 Elsevier Science B.V. All rights reserved.