title: Density functional investigation on electron-transfer catalysis of cycloreversion of cyclobutane: radical anion mechanism.
abstract: The mechanism of cycloreversion of cyclobutane radical anion (c-C(4)H(8) (-)) has been investigated at the UB3LYP/6-31++G(d,p) level, and compared with those of neutral c-C(4)H(8) and c-C(4)H(8) (+) radical cation. Although both c-C(4)H(8) (-) and C(2)H(4) are shown to be Rydberg states unstable with respect to electron ejection, the activation barrier for the "rotating" cycloreversion of c-C(4)H(8) (-) (37.3 kcal/mol) is lower by about 25.2 kcal/mol than that of c-C(4)H(8), and even the intervention of tetramethylene radical anion intermediate may reduce the activation barrier for the cycloreversion of c-C(4)H(8) by about 8.4 kcal/mol, mainly due to stronger electron-deficiency of intermediate biradical species than close-shell cyclobutanes. For the cycloreversion for c-C(4)H(8) (-), side isomerization reaction may be efficiently prevented by the low kinetic stability of tetramethylene radical anion intermediate towards dissociation, just different from the radical cation case. Our theoretical results have suggested the possibility of electron-attachment catalysis of the cycloreversion of some electron-deficient substituted cyclobutanes.
authors.affiliation: State Key Laboratory for Structural Chemistry of Unstable & Stable Species, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People's Republic of China. qzwzhh@hotmail.com
authors.forename: Zheng-Wang
authors.initials: ZW
authors.lastname: Qu
authors.forename: Hui
authors.initials: H
authors.lastname: Zhu
authors.forename: Xing-Kang
authors.initials: XK
authors.lastname: Zhang
authors.forename: Qi-Yuan
authors.initials: QY
authors.lastname: Zhang