The Geometry and Internal Rotational Barrier of Carbamic Acid and Several Derivatives
Journal of Molecular Structure: TheoChem
The geometries of the following carbamate-containing molecules have been optimized at the ab initio SCF level using the MINI-1, 3-21G, and 6-31G* basis sets: carbamic acid, methylcarbamate, ethylcarbamate, N-methyl methylcarbamate, N,N-dimethyl methylcarbamate, N-vinyl methyl-carbamate and N-phenyl methylcarbamate. The latter two basis sets yield geometries in best agreement with experimental data. Calculated energy barriers for rotation about the CN bond become progressively higher as the basis set is enlarged; electron correlation leads to a modest reduction. At the MP2/6-31G*//6-31G* level, the barriers lie in the range of 80–90 kJ mol−1. Alkyl substitution on either end of the carbamate group increases the +C=O− charge separation. N-substitution reduces the electron density on the nitrogen whereas the negative charge of this atom is increased by esterification of carbamic acid.
The Geometry and Internal Rotational Barrier of Carbamic Acid and Several Derivatives M. Remko and S. Scheiner J. Mol. Struct., Theochem, 1988 180, 175-188.