3,3-Dimethyl-2-butanol cannot be prepared by:
(A) Reaction of the given aldehyde with MeMgBr followed by H3O+
(B) Acid-catalysed hydration of the given alkene
(C) Ozonolysis followed by reduction using NaBH4/MeOH
(D) Reduction using LiAlH4/H3O+
(E) Acid-catalysed hydration of the given alkyne using Hg2+/H+
Choose the correct answer from the options given below:
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Always check whether the reaction changes the carbon skeleton or oxidation level when predicting the feasibility of alcohol synthesis.
The target compound is 3,3-dimethyl-2-butanol, which is a secondary alcohol.
Step 1: Analyze option (A).
Reaction of an aldehyde with \( \mathrm{MeMgBr} \) followed by acidic workup gives a secondary alcohol.
The given aldehyde structure leads to the formation of 3,3-dimethyl-2-butanol.
Hence, option (A) can prepare the given alcohol.
Step 2: Analyze option (B).
Acid-catalysed hydration of the given alkene proceeds via a carbocation intermediate.
Due to rearrangement (hydride or alkyl shift), the product formed is not 3,3-dimethyl-2-butanol.
Hence, option (B) cannot prepare the given alcohol.
Step 3: Analyze option (C).
Ozonolysis followed by reductive workup cleaves the double bond to give carbonyl compounds, which on reduction yield alcohols.
However, the given alkene skeleton does not regenerate the required carbon framework of 3,3-dimethyl-2-butanol.
Hence, option (C) cannot prepare the given alcohol.
Step 4: Analyze option (D).
Reduction of the given ketone using \( \mathrm{LiAlH_4} \) followed by acidic workup gives the corresponding secondary alcohol.
Thus, option (D) can prepare 3,3-dimethyl-2-butanol.
Step 5: Analyze option (E).
Acid-catalysed hydration of terminal alkynes using \( \mathrm{Hg^{2+}} \) gives ketones (via enol–keto tautomerism), not alcohols.
Hence, option (E) cannot prepare the given alcohol.
Step 6: Final conclusion.
The methods which cannot prepare 3,3-dimethyl-2-butanol are B and E.
