8. Elimination Reactions

When 2-bromo-3-phenylbutane is treated with sodium methoxide, two alkenes result (by E2 elimination). The Zaitsev product predominates.

b. When one pure stereoisomer of 2-bromo-3-phenylbutane reacts, one pure stereoisomer of the major product results. For example, when (2R,3R)-2-bromo-3-phenylbutane reacts, the product is the stereoisomer with the methyl groups cis. Use your models to draw a Newman projection of the transition state to show why this stereospecificity is observed.

c. Use a Newman projection of the transition state to predict the major product of elimination of (2S,3R)-2-bromo-3-phenylbutane.

d. Predict the major product from elimination of (2S,3S)-2-bromo-3-phenylbutane. This prediction can be made without drawing any structures, by considering the results in part (b).

When the following reactions are carried out under the same conditions, the rate constant for the first reaction (k_H) is found to be 7 times greater than the rate constant for the second reaction (k_D). What does that tell you about the mechanism of the reaction? (Hint: a C—D bond is 1.2 kcal/mol stronger than a C—H bond.)

cis-4-Bromocyclohexanol and trans-4-bromocyclohexanol form the same elimination product but a different substitution product when they react with HO⁻.

a. Why do they form the same elimination product?

a. Explain why 1-bromo-2,2-dimethylpropane has difficulty undergoing both S_N2 and S_N1 reactions.

b. Can it undergo E2 and E1 reactions?

Which of the following is the least reactive substrate in an $E_2$ reaction?

Which of the following conditions will most likely promote an $E2$ reaction with an alkyl halide?

Which of the following alkyl chlorides will afford only a single alkene product ($A$) exclusively under $E2$ reaction conditions?