AB INITIO calculation of rotation barrier around of A-X bond in molecules YAXH2 (Y=H,F; A=O,S; X=B,Al,C+,Si+,Be-,Mg-)

Isomers of YAXH2 molecule ( Y=H,F; A=O,S; X=B,Al,C+,Si+,Be-,Mg-) with plane and perpendicular arrangement of groups YA and XH2 were studied by nonempiric method. All the geometric parameters were fully optimized in valency-splitted basis 3-21G*, initiating polarization functions in all the atoms. It is shown that the barriers of hydride structure rotations around A-X bond decrease, when passing from X, belonging to the second period, to X, belonging to the third period, and in the series A=S,O (for all X except X=Be-). In contrast to hydrides, in fluorides transfer from plane (1) to perpendicular (2) arrangement of groups H2X and AF results in additional stabilization of structure 2 at the expense of appearance of X-F bond and cycle formation