Electronic Structures and Reactivities of Aliphatic Small Membered-Ring Compounds. II

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Abstract
Extended Hückel MO investigations of the physico-chemical properties of cycloalkanes have been carried out. The calculated total energies of protonated cyclopropane and cyclopentane show that the most stable configuration of protonated cycloalkanes is the one with the conformation in which a proton exists in the ring plane. In cyclopropane, the changes in the total electronic energies and in the charge distributions caused by the protonation are almost the same as those in ethylene, while no remarkable changes in these quantities can be observed in protonated cyclopentane. It may be concluded that cyclopropane has unsaturated properties similar to those of the π-electron system in its ring plane. Further, the reaction mechanism and the reactivities of halogenocycloalkanes in the SN2-type reaction are discussed. It is shown that the theoretical results can successfully explain their chemical reactivities.