8. Elimination Reactions

Showing 5 of 5 videos

Practice this topic

A chemist allows some pure (2S,3R)-3-bromo-2,3-diphenylpentane to react with a solution of sodium ethoxide (NaOCH2CH3) in ethanol. The products are two alkenes: A (cis-trans mixture) and B, a single pure isomer. Under the same conditions, the reaction of (2S,3S)-3-bromo-2,3-diphenylpentane gives two alkenes, A (cis-trans mixture) and C. Upon catalytic hydrogenation, all three of these alkenes (A, B, and C) give 2,3-diphenylpentane. Determine the structures of A, B, and C; give equations for their formation; and explain the stereospecificity of these reactions.

609

Predict the elimination products of the following reactions, and label the major products. b. trans-1-bromo-2-methylcyclohexane+NaOCH3 in CH3OH

719

Predict the elimination products of the following reactions, and label the major products. a. cis-1-bromo-2-methylcyclohexane+NaOCH3 in CH3OH

1544

When the following stereoisomer of 2-bromo-1,3-dimethylcyclohexane is treated with sodium methoxide, no E2 reaction is observed. Explain why this compound cannot undergo the E2 reaction in the chair conformation.

NaOCH3, CH3OH—> no alkene produced HINT: Look for a hydrogen trans to the leaving group; then see if the hydrogen and the leaving group can become diaxial.

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

c. <IMAGE>

d. <IMAGE>

309

a. Design an alkyl halide that will give only 2,4-diphenylpent-2-ene upon treatment with potassium tert-butoxide (a bulky base that promotes E2 elimination).

b. What stereochemistry is required in your alkyl halide so that only the following stereoisomer of the product is formed?

H3CC(Ph)=C(CH(Ph)CH3)H

248

One of the following dichloronorbornanes undergoes elimination much faster than the other.

Determine which one reacts faster, and explain the large difference in rates.

Cis <IMAGE> or trans <IMAGE> (CH3)3CO-K+, (CH3)3COH-> <IMAGE>

252

Give the expected product(s) of E2 elimination for each reaction. (Hint: Use models!)

a. <IMAGE> NaOCH3—> one product

204

The cis-diastereomer undergoes E2 elimination 500 times faster than the trans form. Explain.

415

Which reactant in each of the following pairs undergoes an elimination reaction more rapidly? Explain your choice. a. (CH3)3CCl→CH3O− or (CH3)3CBr→CH3O− b.

Explain why only a substitution product and no elimination product is obtained when the following compound reacts with sodium methoxide:

561

For each of the following compounds, draw the product that forms in an E2 reaction and indicate its configuration: b. (1S,2R)-1-bromo-1,2-diphenylpropane

617

Why do cis-1-bromo-2-ethylcyclohexane and trans-1-bromo-2-ethylcyclohexane form different major products when they undergo an E2 reaction?

541