EFFECT OF ORBITAL OVERLAP IN THERMAL REVERSE HOMO-DIELS-ALDER REACTION AND INTRAMOLECULAR REVERSE ENE REACTION

Semiempirical calculations of activation energies confirm the importan ce of orbital overlap effect on thermal reverse homo-Diels-Alder. reac tions and intramolecular reverse ene reactions. Computations of the tr ansition states of cis-3,6-dimethyl-3,6-dihdropyridazine, 2,5-dimethyl -3,4-diaza bicyclo[4.1.0]hept-3-ene, 2,5-dimethyl-3,4-diaza bicyclo[4. 2.0]oct-3-ene and ropyl-1-d(3))-1(S)-(1(E)-propenyl-2-d)cyclopropane i ndicate that activation energies are considerably decreased when optim al overlap is accomplished. The orbital overlap effect overcomes the s teric effect in intramolecular reverse ene reaction of compounds such as ropyl-1-d(3))-1(S)-(1(E)-propenyl-2-d)cyclopropane in which R is a chlorine atom or a methyl group.