Conformation analysis and computation of energy barrier to rotation about CN bond in para-methylphenyl carbamate and its solvent dependence in comparison with tertiary carbamates and tertiary amides

Barrier to rotation about conjugated CN bond in p-Methyl phenyl carbamate (PMPC) was computed 14–16 kcal/mol at three levels of HF, B3LYP and MP2 using 6-311++G∗∗ basis set. The solvent effect and energy barriers about CN bond in PMPC were compared to the case of tertiary carbamates and tertiary amides. Moreover, it is shown that in primary carbamates such as PMPC and tertiary amides isomerisation process passes through TS2 and TS1 respectively, while in tertiary carbamates goes through a combination of both TSs. Furthermore, X-ray analysis which is reported for the first time for primary aryl carbamates demonstrated that the inclusive plane of carbamate functional group is perpendicular to the plane of phenyl ring. The results of computations are completely in agreement with the X-ray data.