Ab initio SCF and Cl calculations employing a double f Gaussian basis have been carried out to deduce minimum energy surfaces for the electrocyclic transformations of the cyclopropyl cation, radical, and anion respectively to the corresponding allylic species. In each of the symmetry-forbidden interconversions, it is concluded that the ring-opening phase does not occur simultaneously with the actual CH2 rotation. In the allowed disrotatory process of the cation, the methylene rotation begins very shortly after CC stretch is initiated and thereafter the two types of geometrical changes proceed in a synchronous fashion for virtually the entire reaction. Nevertheless, the calculations indicate that in the allowed (conrotatory) anion interconversion CH2 rotation and ring opening again occur in well-separated phases, just as in fact was found before for the allowed thermochemical transformation of cyclobutene and butadiene. The different patterns of behavior in this respect are seen to be related to distinctions in the relative stabilities of the various ring compounds. The importance of Cl in the calculations for the C3H5 systems is much smaller than has been noted in the earlier C4H6 study, with the result that the differences in the activation energies of the respective forbidden and allowed processes for both the cation and anion are calculated to be much greater than the corresponding difference in the cyclobutene-butadiene case. Analysis of a number of energy terms for the dis and con modes of the various C3H5 transformations suggests that the agree-(1) (a) Instituí für Physikalische Chemie; (b) Lehrstuhl für Theoretische Chemie; (c) University of Nebraska.(2) W.

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