Is the mechanism of the [2+2]cycloaddition of cyclopentyne to ethylene concerted or biradical? A completely renormalized coupled cluster study
Makaleler > Tam Makale · 2005
Yazarlar: Armağan KINAL, PİOTR PİECUCH
JOURNAL OF PHYSICAL CHEMISTRY A, SCI Expanded İndekslerine Giren Dergi, Uluslararası, 2005, cilt 110, ss 367-378
DOI: 10.1021/jp0513216
Özet
The mechanism of the [2+2] cycloaddition reaction of cyclopentyne to ethylene has been studied using the completely renormalized coupled cluster method with singles, doubles, and noniterative triples (CR-CCSD(T)). In agreement with the experimentally observed stereochemistry, the CR-CCSD(T) method favors the concerted pathway involving a [2+1] transition state, whereas the popular CCSD(T) method, which is often regarded as the "gold standard" of electronic structure theory, and low-order multireference methods support the less probable biradical mechanism. In addition, the CCSD(T) approach produces an erroneous description of some transition states and intermediates, particularly those which have a significant biradical character. The CR-CCSD(T) calculations indicate that the reaction is a highly exothermic (Delta G(r)(298) = -68 kcal/mol), predominantly concerted process with a relatively low activation barrier on the order of 13- 16 kcal/mol which permits its thermal occurrence.