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A Complete Active Space Self‐Consistent Field (CASSCF) Study of the Reaction Mechanism of the α ‐Alkynone Rearrangement
Author(s) -
Kaneti Jose
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(20000412)83:4<836::aid-hlca836>3.0.co;2-b
Subject(s) - chemistry , acetylene , carbene , complete active space , computational chemistry , concerted reaction , reaction mechanism , photochemistry , density functional theory , organic chemistry , catalysis , basis set
The pyrolytic rearrangement of α ‐alkynones has been discovered by Karpf and Dreiding [1] in 1979. The mechanism of this reaction, which involves an acetylene‐vinylidene rearrangement followed by cyclization of the intermediate vinylidene carbene by insertion into a β ‐C−H bond, has been debated in a couple of theoretical investigations. Restricted Hartree‐Fock (RHF) and single‐point Møller‐Plesset 2 (MP2) calculations at the RHF geometries apparently indicate the carbene cyclization to be the rate‐determining step, contrary to chemical intuition. However, larger‐scale correlated calculations with completely optimized molecular geometries ((8,8) CASSCF/6‐311G**), augmented with a perturbative account for the dynamic correlation contribution to the electronic energy, show vanishing energy barriers to the cyclization step and large activation energies for the acetylene‐vinylidene rearrangement, which is thus confirmed as the rate‐determining step of the title reaction.