Question

Acid-catalyzed dehydration of secondary and tertiary alcohols proceeds through an E1 mechanism. The first step is the protonation of the alcohol oxygen to form an oxonium ion. 

Dehydration of 3-methyl-2-butanol forms one major and two minor organic products. Draw the structures, including hydrogen atoms, of the three organic products of this reaction.

Answer 1

Concepts and reason

Acid catalyzed dehydration: Alcohols undergo elimination reactions to form alkenes and water in the presence of strong acids.

In this reaction, the dehydration of a water molecule takes place.

Alkene formation takes place with the help of E1 mechanism and it obeys Zaitsev’s rule.

Reactivity of alcohol: ${{\rm{3}}^{\rm{0}}}{\rm{ > }}\,\,{{\rm{2}}^{\rm{0}}}{\rm{ > }}\,{{\rm{1}}^{\rm{0}}}$

Fundamentals

Zaitsev’s rule: This rule states that, in an elimination reaction, the product that is more substituted is represented as a stable product.

Example for elimination reaction (E1):

In the above reaction, the alkene product formed from carbocation intermediate can undergo rearrangement.

Ans:

Answer 2