STEREOSELECTIVITY OF NUCLEOPHILIC-ADDITION TO SUBSTITUTED CYCLOHEXANONES - A STRUCTURE AND CHARGE-DENSITY STUDY

Theoretical electron density and transition s tate studies have been carried out on monosubstituted cyclohexanones and heterocyclohexanones. The electron density studies reveal no significant difference in the extent of charge depletion on the two sides of the carbonyl plane. The transition state studies show that for the 4-axially-substituted cyclohexanones the increased preference for axial attack is a result of the large barrier for equatorial attack. The transition state stabilization model cannot explain these results. The results show that the electrostatic field difference between the two sides of the carbonyl plane affects the stereoselectivity. For molecules in which the ring is flat, a relationship between electron density in the axial C-H bonds at the C2 and C6 positions and preference for axial attack is observed as a result of increased torsional strain for equatorial attack.