Questions: When heated in the presence of H+, menthol reacts to form two alkenes. In the reaction above, which alkene is the major product? Circle it above and justify your answer.

When heated in the presence of H+, menthol reacts to form two alkenes. In the reaction above, which alkene is the major product? Circle it above and justify your answer.

Transcript text: b. When heated in the presence of $\mathrm{H}+$, menthol reacts to form two alkenes. In the reaction above, which alkene is the major product? Circle it above and justify your answer.

Solution

Solution Steps

Step 1: Understand the Reaction

Menthol, when heated in the presence of an acid ($\mathrm{H}^+$), undergoes a dehydration reaction. This reaction involves the removal of a water molecule, resulting in the formation of alkenes. The reaction typically follows the E1 mechanism, where the formation of a carbocation intermediate is a key step.

Step 2: Identify Possible Alkenes

In the dehydration of menthol, the hydroxyl group is protonated and leaves as water, forming a carbocation. The location of the carbocation determines the possible alkenes. Menthol can form a secondary carbocation, which can rearrange to a more stable tertiary carbocation. The alkenes are formed by the elimination of a hydrogen atom from a carbon adjacent to the carbocation.

Step 3: Determine the Major Product

According to Zaitsev's rule, the major product of an elimination reaction is the more substituted alkene, as it is more stable. In this case, the tertiary carbocation will lead to the formation of the more substituted alkene as the major product.

Final Answer

The major product of the reaction is the more substituted alkene formed from the tertiary carbocation. $\boxed{\text{The major product is the more substituted alkene.}}$

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