DENSITY-FUNCTIONAL APPROACH TO REGIOCHEMISTRY, ACTIVATION-ENERGY, ANDHARDNESS PROFILE IN 1,3-DIPOLAR CYCLOADDITIONS

The principle of hard and soft acids and bases has been applied in a l ocal sense to rationalize the regiochemistry in cycloaddition reaction of a few typical 1,3-dipoles with phosphorus-containing dipolarophile s. It has been observed in most cases that the transition state with h igher hardness is associated with lower activation energy. The hardnes s profile has also been investigated for these cycloaddition reactions ; while the hardness value goes through a minimum along the reaction c oordinate, its minimum does not coincide with the energy maximum.