THEORETICAL-STUDY OF ELECTRONIC AND STERIC EFFECTS IN THE DEHYDRATIONSTEP OF NORCANPHOR AND SUBSTITUTED NORCANPHOR

The semiempirical AMI method has been employed to calculate the dynami cs of the dehydration step of norcanphor and 3-CH3, 3-OH and 3-Cl subs tituted norcanphor. The reaction paths were obtained for two possible mechanisms: specific acid and general acid catalysis, The geometries h ave been fully optimized for the reactant, activated complexes and pro duct for distinct mechanisms of the general acid catalysis. For norcan phor, the activation barrier obtained for specific acid catalysis was 14.12 kcal mol(-1) while for the general acid catalysis this value is reduced to 4.35 kcal mol(-1). Reaction-coordinate eigenvector analysis shows a breaking of the C-O bond at transition states with the centra l carbon atom positively charged and in a configuration near sp(3) hyb ridization. The results indicate that, during the dehydration step, th e central carbon makes a transition from an sp(3)-like to an sp(2)-lik e hybridization, which allows complete conjugation with the nitrogen a tom, resulting in a carbon-nitrogen double bond. (C) 1998 Elsevier Sci ence B.V.