title: Solvolysis of 1,1-dimethyl-4-alkenyl chlorides: evidence for pi-participation.
abstract: Tertiary 1,1-dimethyl-4-alkenyl chloride (1) solvolyzes with significantly reduced secondary beta-deuterium kinetic isotope effect (substrate with two trideuteromethyl groups) and has a lower entropy and enthalpy of activation than the referent saturated analogue 4 (k(H)/k(D) = 1.30 +/- 0.03 vs k(H)/k(D) = 1.79 +/- 0.01; Delta Delta H(++) = -9 kJ mol(-1), Delta Delta S(++) = -36 J mol(-1) K(-1), in 80% v/v aqueous ethanol), indicating participation of the double bond in the rate-determining step. Transition structure 1-TS computed at the MP2(fc)/6-31G(d) level of theory revealed that the reaction proceeds through a late transition state with considerably pronounced double bond participation and a substantially cleaved C-Cl bond. The doubly unsaturated compound 3 (1,1-dimethyl-4,8-alkadienyl chloride) solvolyzes with further reduction of the isotope effect, and a drastically lower entropy of activation (k(H)/k(D) = 1.14 +/- 0.01; DeltaS(++) = -152 +/- 12 J mol(-1) K(-1), in 80% v/v aqueous ethanol), suggesting that the solvolysis of 3 proceeds by way of extended pi-participation, i.e., the assistance of both double bonds in the rate-determining step.
authors.affiliation: Faculty of Pharmacy and Biochemistry, Department of Chemistry, University of Zagreb, A. Kovacića 1, P.O. Box 156, 10000 Zagreb, Croatia.
authors.forename: Ivica
authors.initials: I
authors.lastname: Malnar
authors.forename: Sandra
authors.initials: S
authors.lastname: Jurić
authors.forename: Valerije
authors.initials: V
authors.lastname: Vrcek
authors.forename: Zeljka
authors.initials: Z
authors.lastname: Gjuranović
authors.forename: Zlatko
authors.initials: Z
authors.lastname: Mihalić
authors.forename: Olga
authors.initials: O
authors.lastname: Kronja