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The Journal of Physical Chemistry, Vo/. 83, No. 19, 1979
Additians and Corrections
Acknowledgment. The author thanks Professor J. R. Berson for a very fruitful discussion and Professors R. Hoffmann, W. Bailey, G. Epling, and S. Gould for valuable criticism and advice. The computations were performed a t the IBM Thomas J. Watson Research Center. References a n d Notes (1) For an excellent recent review of thermal rearrangements involving cyclopropanes, see: Berson, J. A, Annu. Rev. Pbys. Chem. 1977, 28, 111-132. (2) See Bergman, R. G. "Free Radicals"; Kochi, J., Ed.; New York, N.Y., 1973; Vol. I,pp 191-237. (3) (a) Srinivasan, R.; Ors, J. J . Am. Cbem. SOC.1978, 100, 7089; (b) Ibid. I n press. (4) (a) Currie, C. L.; Okabe, H.; McNesby, J. R. J . Pbys. Chem., 1963, 67, 1494. (b) Hili, K. L,; Doepker, R. D. Ibid. 1972, 76, 3153. (c) Lopez, E.; Doepker, R. D. Ibid. 1978, 82, 753. (d) Scala, A. A.; Ausloos, P. J. Cbem. Phys. 1968, 49, 2282. (e) Skibuya, K.; Obi, K.; Tanaka, J. Bull. Chem. SOC.Jpn. 1975, 48, 1974. (f) Dhingra, A.; Koob, R. D. J . Pbys. Chem. 1970, 74, 4490. (9) Vorachik, J. H.; Koob, R. D. Ibid. 1972, 76, 9. (h) Dees, K.;Koob, R. D. Ibid. 1973, 77, 759. (5) This point was brought up by Professor Berson in ref 1 but a detailed explanation of the effects of substituents with respect to C-C bond cleavage in cyclopropanes has not been given by either experimentalists or theoreticians. However, extended Huckel' calculations on a series of substituted cyclopropanes were performed by Gavezzotti, A.; Simonetta, M. Tetrahedron Lett., 1975, 4155. (6) Hoffmann, R. J . Cbem. Phys. 1963, 39, 1397. (7) The calculations presented here are essentially qualitative and are meant to reproduce only trends in the ring opening of substituted cyclopropanes in the ground and excited states. The small 3 X 3 C I calculations performed in the majority of calculations are not sufficiently extensive to accurately determine the first excited singlet state in cyclopropane and its alkyl derivatives. However, several factors, including a small gap between the highest occupied orbital (HOMO) and lowest unoccupied 4bi orbital (LUMO) and the fact that the 4bl orbital is well separated from the other virtual orbitals lead one to conclude that the first excited state is 'B,. In addition, a much larger C I was performed for an open form of cyclopropane and the Slater determinant in which the 6ai and 4bi orbitals were each singly occupied was found to dominate. A more quantitative calculation on cyclopropane was performed by Buenker, R. J.; Peyerimhoff, S. D. J . Phys. Cbem. 1969, 73, 1299. (8) All results were obtained by using the GAUSSIAN 70 series of programsg and performing SCF calcuialions with the STO-3G basis." Using the molecular orbitals from the SCF procedure, we performed a configuration interaction (CI) by allowing the mixing of all singly and doubly excited configurations obtained by varying the population of the highest occupied orbital of the ground state configuration and the lowest-lying unoccupied orbital yielding a 3 X 3 C I matrix." The bond distances used are C-C, 1.52 A and C-H, 1.09 A; the bond angles were all idealized: 60' for the internal angles of cyclopropane and 109.47' for the angles of all alkyl substituents. The coordinate system employed along with the pertinent Waish orbitals" for cyclopropane labeled according to C p usymmetry is given as follows:
ADDITION
N
(9) Hehre, W. J.; Lathan, W. A,; Ditchfield, R.; Newton, M. D.; Pople, J. A. Quantum Chemistry Program Exchange, Department of Chemistry, Indiana University, Bloomington, Ind., Program No. 236, p 10, 1973. 10) Hehre, W. J.; Stewart, R. F.; Pople, J. A. J. Cbem. Pbys. 1969, 51, 2657. 11) A C I program to interface with the GAUSSIAN 70 program written by M. H. Whangbo, Department of Chemistry, North Carolina State University, Raleigh, N.C. 27650. 12) For complete discussion of the Walsh orbitals of cyclopropane see: (a) Hoffmann, R. Tetrahedron Lett. 1970, 2907. (b) Hoffmann, R.; Davidson, R. 8. J . Am. Cbem. SOC.1971, 93, 5699. (c) Hoffmann, R., "Special Lectures at the XXIII International Congress of Pure and Applied Chemistry"; Butterworths: London, 1971; Vol. 2, p 233. (d) Hoffmann, R.; Stohrer, W . 4 . J. Am. Cbem. SOC.1971, 93, 6941. (e) Stohrer, W.-D.; Hoffmann, R. Angew Cbem., 1972, 84, 820. (f) Hoffmann, R.; Fujimoto, H.; Swenson, J. R.; Wan, C.-C. J. Am. Cbem. SOC. 1973, 95, 7644. (13) The notation used for the uT and L T ~ methyl . group orbitals is that of Libit, L.; Hoffmann, R. J . Am. Chem. SOC. 1974, 96, 1370. (14) A good discussion of methyl group orbitals is given in Jorgensen, W. L.; Salem, L. "The Organic Chemist's Book of Orbitals"; Academic Press: New York, 1973. (15) Muliiken, R. S. J. Cbem. Phys. 1955, 23, 1833, 1841, 2338, 2343. (16) One must be cautious in drawing any conclusions about the mechanism of ring opening in substituted cyclopropane for either the thermal or excited-state reactions. More extensive calculations [similar to (a) Horsley, J. A,; Jean, Y.;Moser, C.; Salem, L.; Stevens, R. M.; Wright, J. S. J . Am. Cbem. SOC.1972, 94, 279. (b) Hay, P. J.; Hunt, W. J.; Goddard, W. A. Ibid. 1972, 94, 6381 must be performed for a cyclopropane molecule in which a C-C bond containing substituents is broken. It would be interesting to determine if there is a minimum corresponding to a biradical intermediate on the substituted trimethylene potential energy surface.
Department of Chemistty University of Connecticut Storrs, Connecticut 06268 Received March 19, 1979
RRECTIONS 1979, Volume 83
M. Nicolas" a n d R. Reich: Ionic Association of Lithium Perchlorate in Low Dielectric Constant Media from Very Dilute Solutions to Saturation a t 293 and 198 K. Pages 749-756. In Table Ib, T = 198 K, column 4 (Ao values) should lead 13.95 (2) for x = 0 (MeOH) and 17.92 (2) for x = 0.176. The following sentence should be included a t the end of the first paragraph in the Results and Discussion section
(p 750): The values of c are intermediate between those o f ref 21 and 24 for MeOH and a little lower than those
given in ref 22 and 23 for THE'.-M.
Nicolas.
A. R. Rossi
