THE DIRECTIONAL CHANGES IN TORSION ANGLES ALONE AFTER COMPLEXATION OFTHE CARBONYL OXYGEN WITH A PROTOTYPICAL CATION SUCH AS H- AN AB-INITIO INVESTIGATION( PREDICT THE FACIAL SELECTIVITY OF SUBSTITUTED CYCLOHEXANONES )

Hf was taken as a prototypical cation for complexation with the carbon yl oxygen of 3-oxa-, 3,5-dioxa-, and 3-thiacyclohexanones. The geometr ies of the complexes were fully optimized using ab initio MO calculati ons with 6-31G basis set. The complexation desymmetrizes the molecular geometry further to an extent that the torsion angle changes on the a xial face can be rationally used for the prediction of the facial sele ctivity in reactions with nucleophiles. The torsion angle changes are sensitive to the nature, position, and orientation of the substituents . (C) 1997 Published by Elsevier Science Ltd.