title: Kinetic stabilization and reactivity of π single-bonded species: effect of the alkoxy group on the lifetime of singlet 2,2-dialkoxy-1,3-diphenyloctahydropentalene-1,3-diyls.
abstract: Kinetic stabilization and reactivity of π single-bonded species have been investigated in detail by generating a series of singlet 2,2-dialkoxy-1,3-diphenyloctahydropentalene-1,3-diyls (DRs). The lifetime at 293 K in benzene was found to increase when the carbon chain length of the alkoxy groups was increased; 292 ns (DRb; OR = OR' = OCH3) <880 ns (DRc; OR = OR' = OC2H5) <1899 ns (DRd; OR = OR' = OC3H7) ≈2292 ns (DRe; OR = OR' = OC6H13) ≈2146 ns (DRf; OR = OR' = OC10H21). DRh (OR = OC3H7, OR' = OCH3; 935 ns) with the mixed-acetal moiety is a longer-lived species than another diastereomer DRg (OR = OCH3, OR' = OC3H7; 516 ns). Activation parameters determined for the first-order decay process reveal that the enthalpy factor plays a crucial role in determining the energy barrier of the ring-closing reaction, that is, from the π-bonding to the σ-bonding compounds. Computational studies using density functional theory provided more insight into the structures of the singlet species with π single-bonded character and the transition states for the ring-closing reaction, thereby clarifying the role of the alkoxy group on the lifetime and the stereoselectivity of the ring-closing reaction.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University (HIRODAI), 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nakagaki
authors.forename: Tomoko
authors.initials: T
authors.lastname: Sakai
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Mizuta
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Manabu
authors.initials: M
authors.lastname: Abe
keywords: density functional calculations; diradicals; kinetics; pi single bonds; substituent effects