Quadricyclane Radical Cation Rearrangements: A Computational Study of the Transformations to 1,3,5-Cycloheptatriene and Norbornadiene
2004 (Swedish)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 10, no 3, 681-688 p.Article in journal (Refereed) Published
An alternative skeletal rearrangement of the quadricyclane radical cation (Q.+) explains the side products formed in the one-electron oxidation to norbornadiene. First, the bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation, with an activation energy of 14.9 kcal mol-1, is formed. Second, this species can further rearrange to 1,3,5-cycloheptatriene through two plausible paths, that is, a multistep mechanism with two shallow intermediates and a stepwise path in which the bicyclo[3.2.0]hepta-2,6-diene radical cation is an intermediate. The multistep rearrangement has a rate-limiting step with an estimated activation energy of 16.5 kcal mol-1, which is 2.8 kcal mol-1 lower in energy than the stepwise mechanism. However, the lowest activation energy is found for the Q.+ cycloreversion to norbornadiene that has a transition structure, in close correspondence with earlier studies, and an activation energy of 10.1 kcal mol-1, which agrees well with the experimental estimate of 9.3 kcal mol-1. The computational estimates of activation energies were done using the CCSD(T)/6-311+G(d,p) method with geometries optimized on the B3LYP/6-311+G(d,p) level, combined with B3LYP/6-311+G(d,p) frequencies.
Place, publisher, year, edition, pages
2004. Vol. 10, no 3, 681-688 p.
Radical ions, Rearrangement, Quadricyclane, Density Functional calculations, Electron spin resonance
IdentifiersURN: urn:nbn:se:uu:diva-14970DOI: 10.1002/chem.200305067OAI: oai:DiVA.org:uu-14970DiVA: diva2:42741