title: The Carbocation Rearrangement Mechanism, Clarified.
abstract: The role of protonated cyclopropane (PCP(+)) structures in carbocation rearrangement is a decades-old topic that continues to confound. Here, quantum-chemical computations (PBE molecular dynamics, PBE and CCSD optimizations, CCSD(T) energies) are used to resolve the issue. PCP(+) intermediates are neither edge-protonated nor corner-protonated (normally) but possess "closed" structures mesomeric between these two. An updated mechanism for hexyl ion rearrangement is presented and shown to resolve past mysteries from isotope-labeling experiments. A new table of elementary-step barrier heights is provided. The mechanism and barrier heights should be useful in understanding and predicting product distributions in organic reactions, including petroleum modification.
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina , 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada.
authors.forename: Daniel J S
authors.initials: DJ
authors.lastname: Sandbeck
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina , 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Markewich
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina , 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada.
authors.forename: Allan L L
authors.initials: AL
authors.lastname: East