Reactivity of some tertiary chlorides with olefinic and methoxy neighboring groups. A case of extended π, n‐participation

Tertiary 2‐chloro‐2‐methyl‐5‐methoxypentane ( 2 ) solvolyzes with a significantly reduced secondary β‐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; ΔΔ H ≠  = −11 kJ mol −1 ; ΔΔ S ≠  = −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; ΔΔ H ≠  = −33 kJ mol −1 ; ΔΔ S ≠  = −106 J mol −1 K −1 , in 80% (v/v) aqueous ethanol], suggesting that the solvolysis of 3 proceeds with extended π, n‐participation, i.e. the assistance of both neighboring groups occurs in the rate‐determining step. Copyright © 2002 John Wiley & Sons, Ltd.