Acid-Catalyzed Dehydration of Alcohols Draw structural formulas for the alkenes formed by the acid-catalyzed dehydration of each alcohol. For each part, predict which alkene will be the major product. (a) 3-Methyl-2-butanol (b) 2-Methylcyclopentanol Strategy In acid-catalyzed dehydration of an

Question

Acid-Catalyzed Dehydration of Alcohols

Draw structural formulas for the alkenes formed by the acid-catalyzed dehydration of each alcohol. For each part, predict which alkene will be the major product.

(a) 3-Methyl-2-butanol

(b) 2-Methylcyclopentanol

Strategy

In acid-catalyzed dehydration of an alcohol, H and OH are removed from adjacent carbon atoms. When dehydration yields isomeric alkenes, the alkene with the greater number of alkyl groups on the carbon atoms of the double bond generally predominates.

Accepted Answer

(a) Elimination of [latex]H _{2} O[/latex] from carbons 2–3 gives 2-methyl-2-butene; elimination of [latex]H _{2} O[/latex] from carbons 1–2 gives 3-methyl-1-butene. 2-Methyl-2-butene has three alkyl groups (three methyl groups) on its double bond and is the major product. 3-Methyl-1-butene has only one alkyl group (an isopropyl group) on its double bond and is the minor product.

(b) The major product, 1-methylcyclopentene, has three alkyl groups on its double bond. The minor product, 3-methylcyclopentene, has only two alkyl groups on its double bond.

Question 14.3: Acid-Catalyzed Dehydration of Alcohols Draw structural formu...

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