9. Alkenes and Alkynes

Identify the alcohol(s) that would produce the following alkenes under the given conditions.

(c)

When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]

(a)

Predict the product of the following pinacol rearrangements.

(c)

Suggest a mechanism for the following reactions.

(c) Elimination:

Suggest a mechanism for the following substitution reaction.

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (vi) H₂SO₄. If no reaction occurs, write 'no reaction.'  

(a)

The acid-catalyzed hydration we learned here in Chapter 8 is reversible:

(c) Which side of the reaction would be favored by running the reaction at high temperatures?

What product is obtained when the following vicinal diol is heated in an acidic solution?

What stereoisomers are formed in the following reactions? Which stereoisomer is the major product?

b. the acid-catalyzed dehydration of 3,4-dimethyl-3-hexanol to 3,4-dimethyl-3-hexene

Indicate which alcohol in each pair undergoes an elimination reaction more rapidly when heated with H₂SO₄.

a.

b.

Explain why (S)-2-butanol forms a racemic mixture when it is heated in sulfuric acid.

Propose a mechanism for the following reaction:

What alkenes would you expect to be obtained from the acid-catalyzed dehydration of 1-hexanol?

Indicate which alcohol in each pair undergoes an elimination reaction more rapidly when heated with H₂SO₄.

e.

Indicate which alcohol in each pair undergoes an elimination reaction more rapidly when heated with H₂SO₄.

d.