56434-65-2Relevant academic research and scientific papers
Borderline between E1 and E2 Mechanisms. Bimolecular Base-Promoted Elimination via Ion Pairs Competing with Concerted E2 Elimination
Thibblin, Alf
, p. 5412 - 5416 (2007/10/02)
The solvolysis of 2-chloro-2-methyl-1-phenylpropane (1) in methanol or in 25 vol percent acetonitrile in water at 25 deg C yields substitution product 2 (ether or alcohol) and the two elimination products 3 and 4.The olefin fraction in the aqueous solution does not increase significantly in the presence of 0.75 M sodium hydroxide.In methanol, on the other hand, the fraction of 3 and 4, the ratio /, and the rate of disappearance of 1 increase with methoxide ion concentration.The kinetic isotope effects (k12H + k13H + k14H)/(k12d2 + k13d2 +k14d2) = 1.41 and 1.42, measured for the solvolysis of the dideuterated analogue d2-1 in water/acetonitrile and in methanol, respectively, are too large to be secondary effects on a rate-limiting ionization step, but they suggest reaction via a reversibly formed carbocationic intermediate.The solvolysis of the hexadeuterated analogue d6-1 exhibits "normal" secondary kinetic isotope effects, (k12H + k13H + k14H)/(k12d6 + k13d6 + k14d6) = 1.79 and 1.81 in water/acetonitrile and methanol, respectively.The presence of 2 M NaOMe increases the isotope effect for d2-1 to 2.4 but decreases the effect for d6-1 to 1.35.These results indicate that 3 is formed by a parallel methoxide-promoted one-step concerted rout (E2) and that such a route is not significant for the formation of 4.The isotope effect for the E2 reaction is estimated as kH/kd2 = 4.9 (on the basis of the assumption that the elimination product ratio / for the carbocationic route is not affected by MeO(1-)).
