Suprafacial -rearrangement of cyclopentadiene C

The orbitals on both sides of the correspondence diagram are [2 x a -h a ] and the rearrangement via the suprafacial transition state in clearly allowed in agreement with both the Woodward-Hoffmann Rules and experiment. It is 

The alternative choice would exchange the symmetry labels of the two anasymmetrized tt orbitals, but the electron configuration would remain the same. 

The strongest presumptive evidence for facile sigmatropic shifts that obey the Woodward-Hoffmann Rules is cited for molecules with a cyclic a frame in which the migrating bond is to carbon rather than to hydrogen [30, pp. 98-103]. A particularly intriguing example, discovered by Berson and Wilcott some 25 years ago [40], is illustrated in Fig. 8.10. 

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