N-inversion and C-N rotational barriers in HX=CH-NH2 (X = N,P,As) compounds: an ab initio study

Ab initio calculations at HF/6-31G* and MP2/6-31G* levels are performed on methanimidamide, 1-phosphinidene methanamine and 1-arsenidene methanamine i n their E and Z conformations. All of them are found to have pyramidal arra ngement around nitrogen of the amino group. Pyramidalization in the amino g roup could be identified only after including electron correlation. The N-i nversion barrier and the C-N rotational barriers in these molecules have be en calculated to understand the electron distribution in these molecules. T he C-N bond length decreases, bond strength increases, N-inversion barrier decreases, C-N rotation barrier increases, flow of charge from N to X incre ases in the order methanimidamide < 1-phosphinidene methanamine < 1-arsenid ene methanamine. It is found that the electronegativity of X can not be tak en as the driving force for the delocalization of electrons onto the a fram ework of the HX = C(H)-NH2 molecules. (C) 1999 Elsevier Science B.V. All ri ghts reserved.