Journal
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
Volume 26, Issue 9, Pages 750-754Publisher
WILEY
DOI: 10.1002/poc.3126
Keywords
phenylenes; biphenylene; rearrangements; polycyclic aromatic hydrocarbons; carbenes
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Funding
- University of San Francisco Faculty Development Fund
- National Science Foundation [CHE-0910971, CHE-1213425]
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Mechanisms of benzene ring contractions in phenylenes were studied using density functional and coupled cluster methods. Rearrangement of biphenylene to benzopentalene can proceed via a carbene route, by initial 1,2-carbon shift followed by a 1,2-hydrogen shift, with a CCSD(T)/cc-pVDZ//B3LYP/6-31G* barrier of similar to 77kcal/mol. An alternative carbene pathway consisting of an initial 1,2-hydrogen shift followed by a 1,2-carbon shift has a slightly higher computed barrier of 79kcal/mol. The preferred carbene mechanism is computed to have a barrier at least 25kcal/mol lower than competing diradical mechanisms at the BD(T)/cc-pVDZ level. The various possible benzene ring contractions in angular [3]phenylene are predicted to have barriers of 79-82kcal/mol, with little preference for one pathway over the others. Thus, mechanistic proposals to explain pyrolysis products of angular [3]phenylene can reasonably invoke any of the four possible initial reaction modes via carbene intermediates. Copyright (c) 2013 John Wiley & Sons, Ltd.
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