Kinetic Stabilization and Reactivity of Single-Bonded Species: Effect of the Alkoxy Group on the Lifetime of Singlet 2,2-Dialkoxy-1,3-diphenyloctahydropentalene-1,3-diyls

Kinetic stabilization and reactivity of 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 293K in benzene was found to increase when the carbon chain length of the alkoxy groups was increased; 292ns (DRb; OR=OR=OCH3) <880ns (DRc; OR=OR=OC2H5) <1899ns (DRd; OR=OR=OC3H7) approximate to 2292ns (DRe; OR=OR=OC6H13) approximate to 2146ns (DRf; OR=OR=OC10H21). DRh (OR=OC3H7, OR=OCH3; 935ns) with the mixed-acetal moiety is a longer-lived species than another diastereomer DRg (OR=OCH3, OR=OC3H7; 516ns). 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 -bonding to the sigma-bonding compounds. Computational studies using density functional theory provided more insight into the structures of the singlet species with 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.