NMR and theoretical study of the (CaO)–N rotational barrier in the isomers cis- and trans- 2-N,N-dimethylaminecyclohexyl 1-N0, N0-dimethylcarbamate

Rotation around the conjugated C–N bond was investigated through dynamic NMR experiments, employing both 1H and 13C spectra, and theoretical calculations (HF and B3LYP with the 6-311CG** and 6-31G** basis sets). Theoretical results predicted slightly distinct gasphase rotational barriers for the isomers, although inclusion of solvation effects causes the barriers to be essentially equal. Experiments corroborate with this result. 1H and 13C spectra provided somewhat different rate constants but the activation parameters (DS‡, DH‡ and DG‡) are very similar for both. Additionally, we investigated the solvent effect through experiments in CDCl3, CD3OD, DMSO-d6 and D2O solutions and SCRF calculations. The results agree with previous studies that the rotational barrier in carbamates is solvent insensitive. q 2005 Elsevier B.V. All rights reserved.