8. Elimination Reactions

When (±)−2,3−dibromobutane reacts with potassium hydroxide, some of the products are (2S,3R)-3-bromobutan-2-ol and its enantiomer and trans-2-bromobut-2-ene. Give mechanisms to account for these products.

Which of the following S_N2 and E2 reactions, respectively, is faster? Justify your choice.

(b)

Predict the product of the following reactions.

(e)

Predict the major and minor elimination products of the following proposed reactions (ignoring any possible substitutions for now). In each case, explain whether you expect the mechanism of the elimination to be E1 or E2.

(a)

Under second-order conditions (strong base/nucleophile), S_N2 and E2 reactions may occur simultaneously and compete with each other. Show what products might be expected from the reaction of 2-bromo-3-methylbutane (a moderately hindered 2° alkyl halide) with sodium ethoxide.

Paying close attention to the stereochemical outcome, predict the product of these elimination reactions.

(a)

Which of the following compounds would react faster in an

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a. E1 reaction?

b. E2 reaction?

Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.

(c)

Predict the products and mechanisms of the following reactions. When more than one product or mechanism is possible, explain which are most likely.

h. 1-bromo-1-methylcyclopentane heated in methanol

Would you expect the following bases to favor E1 or E2 elimination?

(a)

Draw the substitution and elimination products for the following reactions, showing the configuration of each product:

a. trans-1-chloro-2-methylcyclohexane + CH₃O⁻

Predict the product of the following reactions.

(d)

Pure (S)-2-bromo-2-fluorobutane reacts with methoxide ion in methanol to give a mixture of (S)-2-fluoro-2-methoxybutane and three fluoroalkenes.

b. Propose a mechanism to show how (S)-2-bromo-2-fluorobutane reacts to give (S)-2-fluoro-2-methoxybutane. Has this reaction gone with retention or inversion of configuration?

Identify whether each of the following reactions proceed by an S_N1, S_N2, E1, or E2 mechanism.

(c)