RESUMO
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 293â K in benzene was found to increase when the carbon chain length of the alkoxy groups was increased; 292â ns (DRb; OR = OR' = OCH3) <880â ns (DRc; OR = OR' = OC2H5) <1899â ns (DRd; OR = OR' = OC3H7) ≈2292â ns (DRe; OR = OR' = OC6H13) ≈2146â ns (DRf; OR = OR' = OC10H21). DRh (OR = OC3H7, OR' = OCH3; 935â ns) with the mixed-acetal moiety is a longer-lived species than another diastereomer DRg (OR = OCH3, OR' = OC3H7; 516â 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.