9 - C8H6−C8H14

Abstract

This chapter presents hydrocarbon isomerizations, which have been at or near the center of experimental and theoretical efforts by physical organic chemists, such as C8H6, C8H8, C8H10, and C8H12. Cyclooctatetraene (COT), a 4n non-aromatic hydrocarbon, is only one of the many (CH)8 compounds, but it is a central character. COT is nonplanar, no doubt due to the angle strain in the planar form. At elevated temperatures, COTs undergo carbon scrambling as revealed by substituted materials. Benzocyclobutenes have been found to ring open to very reactive o-quinodimethanes, which can be trapped by various dieneophiles. Attempts to determine the stereochemistry of the cyclization were thwarted by the rapid hydrogen shifts. Because the BDE of the C1–C2 bond is roughly 32 kcal/mol by virtue of cyclobutane ring strain and formation of two allyl radicals, it is likely that the rearrangement is a concerted 3,3-shift. However, it must proceed via a boatlike transition state with the vinyl groups over the ring, so that cis double bonds are generated in the major product.