12. Alcohols, Ethers, Epoxides and Thiols

Suggest the appropriate reagents to carry out the following transformations.

(d)

Show how you would use a simple chemical test to distinguish between the following pairs of compounds. Tell what you would observe with each compound.

(d) allyl alcohol and propan-1-ol

(e) butan-2-one and tert-butyl alcohol

Predict the product of the following reactions.

(c)

What product would be formed if the four-membered ring alcohol in Problem 70 were heated with an equivalent amount of HBr rather than with a catalytic amount of H₂SO₄?

When 3-methyl-2-butanol is heated with concentrated HBr, a rearranged product is obtained. When 2-methyl-1-propanol reacts under the same conditions, a rearranged product is not obtained. Explain.

Predict the product of the following reactions.

(a)

Suggest the appropriate reagents to carry out the following transformations.

(a)

Suggest a mechanism for the following reactions.

(b) Substitution :

(b) Under the same conditions, an optically active sample of trans-2-bromocyclopentanol reacts with concentrated aqueous HBr to give an optically inactive product, (racemic) trans-1,2-dibromocyclopentane. Propose a mechanism to show how this reaction goes with apparently complete retention of configuration, yet with racemization. (Hint: Draw out the mechanism of the reaction of cyclopentene with Br₂ in water to give the starting material, trans-2- bromocyclopentanol. Consider how parts of this mechanism might be involved in the reaction with HBr.)

(a) The reaction of butan-2-ol with concentrated aqueous HBr goes with partial racemization, giving more inversion than retention of configuration. Propose a mechanism that accounts for racemization with excess inversion.

Predict the product of the following reactions.

(b)

Propose a mechanism for the reaction of

(a) 1-methylcyclohexanol with HBr to form 1-bromo-1-methylcyclohexane.

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

(a)

Triphenylphosphine and iodine can be used to convert alcohols to iodoalkanes. Suggest a mechanism for this reaction. [Triphenylphosphine first acts as a nucleophile in this reaction.]

Propose mechanisms for the following reactions. In most cases, more products are formed than are shown here. You only need to explain the formation of the products shown, however.

(a)