Sd. Junior et al., THEORETICAL-STUDY OF ELECTRONIC AND STERIC EFFECTS IN THE DEHYDRATIONSTEP OF NORCANPHOR AND SUBSTITUTED NORCANPHOR, Journal of molecular structure. Theochem, 427, 1998, pp. 229-235
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.