AN AB-INITIO MO STUDY OF PERFLUORO-EFFECT IN THERMAL CYCLIZATION OF BUTA-1,3-DIENE TO CYCLOBUTENE

Ab initio theoretical studies at SCF and MP2 levels with various basis sets on thermal cyclization of perfluorobuta-1,3-diene (3) to perfluo rocyclobutene (4) confirm the experimentally observed reversal of rela tive stabilities on perfluorination of buta-1,3-diene (1) and cyclobut ene (2). The transition structures follow Hammond's postulate. The eff ect of fluorine substitution on sp(2) and sp(3) hybridized carbon cent res are analysed using the relative energies of mono-, di-, tri- and t etra-fluoroderivatives of butadiene and cyclobutene (5-18) at HF/6-31G level. The reversal of relative stabilities on perfluorination is at tributed to the increasing destabilization on polyfluorination at sp(2 )-C.