Question

multiple choice 2 points
predict the major product of the reaction shown below.
oh h₃po₄, heat
2,4 - dimethyl - 1 - butene
2,2 - dimethyl - 2 - butene
2,3 - dimethyl - 2 - butene
2,3 - dimethyl - 1 - butene
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Explanation:

Step1: Dehydration reaction mechanism

The reaction is an acid - catalyzed dehydration of an alcohol. The hydroxyl group (\(OH\)) is protonated by \(H_3PO_4\) to form a good leaving group (\(H_2O\)).

Step2: Carbocation formation

After the loss of \(H_2O\), a carbocation is formed.

Step3: Carbocation rearrangement (if necessary)

In this case, the carbocation can rearrange (not required here as per the structure) or follow Zaitsev's rule.

Step4: Product formation based on Zaitsev's rule

Zaitsev's rule states that the more substituted alkene is the major product. 2,3 - dimethyl - 2 - butene is more substituted (has more alkyl groups attached to the double - bond carbons) compared to the other options.

• 2,4 - dimethyl - 1 - butene: Less substituted.
• 2,2 - dimethyl - 2 - butene: Not a valid structure (violates carbon - valency rules in a simple sense for this context).
• 2,3 - dimethyl - 1 - butene: Less substituted than 2,3 - dimethyl - 2 - butene.

Answer:

2,3-dimethyl-2-butene