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?

What is the major elimination product obtained from an E2 reaction of each of the following alkyl halides with hydroxide ion?

e.

What products will be obtained from the E2 reaction of the following alkyl halides?

a.

Draw the major product obtained when each of the following alkyl halides undergoes an E2 reaction:

e.