The transition state 3 is nearly a pure biradical (a. ... Acknowledgment. This work was supported in part (PJJAT) by the Netherlands Foundation for Chemical Research (SON) with financial aid from the Netherlands Organization for the Advancement of Pure research (ZWO). Registry No. Cyclohexene, 110-83-8. Supplementary Material Available: Complete geometry specifications (2 matrices, Cartesian coordinates, and important geometric parameters) of 1-3 (4 pages). ...