7147collapses to one identical with that calculated for initial attack perpendicular to the plane.The orbital situation outlined above is by no means uncommon, so that Skell's suggestion' that there may be more cases of excited-state radical generation is almost certainly correct. The search for further examples can, however, be greatly facilitated by preliminary screening of likely precursors by molecular orbital theory. Schleyer for support and encouragement and Dr. J. Chandrasekhar and Dr. P. Hofmann for helpful discussions. This work was facilitated by the cooperation of the staff of the Regionales Rechenzentrum Erlangen.
Supplementary Material Available: Summaries of M N D O resultsfor NCS and the two succinimidoyl radicals ( 3 pages). Ordering information is given on any current masthead page.
References and Notes(1) See Skell, P. S.; Day, J. C. Acc. Chem. Res. 1978, 7 7, 381, and references therein.(2) INDO calculations (Koenig, T.; Wielesek, A. Tetrahedron Lett. 1975Lett. , 2007 suggest that the uo radical may also be low in energy. We have been unable to calculate this species directly," but the reaction paths give only the s and ON radicals. (3) Dewar, M. J. S.; Thiel, W. J. Am. Chem. Soc. 1977, 99, 4899, 4907. Dewar, M. J. S.; McKee, M. L.; Rzepa, H. S. /bid. 1978, 700, 3607. (4) All radical calculations employed the half-electron method: Dewar, M. J. S.; Hashmall, J. A,; Vernier, C. G. J. Am. Chem. SOC. 1968, 90, 1953. Dewar, M. J. S.; Trinajstic, N. J. Chem. SOC. A 1971, 1220. (5) The MNDO geometry for NCS is in good agreement with the X-ray structure: Brown, R. N. Acta Crystallogr. 1961, 74, 711. (6) Howard, P. B.; Skinner, H. A. J. Chem. SOC. A. 1966, 1536.