COMPUTACIONAL STUDY OF THE ELECTRONIC EFFECTS IN ROTATIONAL BARRIER OF THE N-ARILCARBAMATOS N-CO BOND

Abstract

Amides are the subject of many particularly important studies, as their properties are of interest to different areas, spanning from biochemistry to material sciences because this functional group is present, for instance, in both natural and artificial polymers such as proteins and polyamides. Amides and their derivatives show, frequently, two different equilibrium geometries, which result from an energetic barrier involved on the N-CO bond rotation. The rotational mechanism is influenced by electronic and steric effects. In this sense, amides and carbamates from aniline are particularly interesting substrates, since those effects can be evaluated through aryl or nitrogen substituents. In this work, the N-arylcarbamates N-CO rotational mechanisms were studied by AM1 semi-empiric and HF/6-31G* ab initio calculation. The conformational analysis showed, as expected, two equilibrium geometries and two maximum energies rotamers (transition states TSsyn and TSanti).The rotational barriers were calculated by the energies differences between transition states and equilibrium geometries. Barriers were estimated at 13-17 kcal.mol-1 by the HF/6-31G* calculation. AM1 results, by the other side, are about 40% from the ab initio ones.