engleski

Reactivity of some tertiary chlorides with olefinic and methoxy neighbouring groups. A case of extended pi, n-participation.

Tertiary 2-chloro-2-methyl-5-methoxypentane (2) solvolyzes with a significantly reduced secondary beta-deuterium kinetic isotope effect (substrate with two trideuteromethyl groups), and with smaller entropy and enthalpy of activation than the reference saturated analog 4 [k(H)/k(D) = 1.35 +/- 0.01 VS k(H)/k(D) = 1.79 +/- 0.01 ; DeltaDeltaH(not equal) = -11 kJ mol(-1) ; DeltaDeltaS(not equal) = -30 J mol(-1) K-1, in 80% (v/v) aqueous ethanol], indicating participation of the methoxy group in the rate-determining step. 2-Chloro-2, 5-dimethyl-8-methoxy-5(E)-octene (3) solvolyzes with a further reduction of the isotope effect, and drastically smaller activation parameters [k(H)/k(D) = 1.16 +/- 0.01 ; DeltaDeltaH(not equal) = -33 kJ mol(-1) ; DeltaDeltaS(not equal) = -106 J mol(-1) K-1, in 80% (v/v) aqueous ethanol], suggesting that the solvolysis of 3 proceeds with extended pi, n-participation, i.e. the assistance of both neighboring groups occurs in the rate-determining step.

Secondary beta-deuterium isotope effects. Tertiary chlorides. Extended pi; n-participation. Solvolysis.

nije evidentirano