Cope rearrangement degenerate reaction

The Marcus equation provides a nice conceptual tool for understanding trends in reactivity. Consider for example the degenerate Cope rearrangement of 1,5-hexadiene and the ring-opening of Dewar benzene (bicyclo-[2,2,0]hexa-2,5-diene) to benzene. Figure 15.29. The experimentally observed activation energies are 34 kcahmol and 23 kcal/mol, respectively. The Cope reaction is an example of a Woodward-Hoffmann... 

This reaction is said to be a structurally degenerate Cope rearrangement. ... 

Bridged derivatives of homotropylidene also undergo extremely facile degenerate Cope rearrangements. Perhaps the most intriguing of these reactions involves the substance tricyclo[3.3.2.0 ]deca-2,7,9-triene, or bull-valene (XIII). Bullvalene can have its ten carbon atoms arranged in more than... 

Figure 1.6 Part of the extended reaction network connecting multiple isomers of bullvalene via degenerate Cope rearrangements. Aithough the structure seems to remain unchanged, note that the blue carbon atom moves away from the black atom.

A homo-1,4-elimination occurs on reaction of the anti-bishomoquinone derivatives (624 R = Me or Ar) with phosphorus iodide cf. p. 97). The n.m.r. spectra of the products (625) show temperature dependence due to a degenerate Cope rearrangement With phosphorus tribromide (624 . R = Me) undergoes a double homoallylic rearrangement to give (626). °... 

GonzAlez-Navarrete P, Andres J, Berski S (2012) How a quantum chemical topology analysis enables prediction of electron density transfers in ehemieal reactions. The degenerated cope rearrangement of semibullvalene. J Phys Chem Lett 3 2500-2505... 

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