Question

What is the IUPAC name of the organic compound formed in the following chemical reaction?
Acetone \( \xrightarrow{\text{(i) } C_{2}H_{5}MgBr,\ \text{dry ether} \;\;\text{(ii) } H_{2}O,\ H^{+}} \) Product

• A. Pentan-2-ol
• B. Pentan-3-ol
• C. 2-methyl butan-2-ol
• D. 2-methyl propan-2-ol
• E.

Hint:

Count the total number of carbons: Acetone (3 carbons) + Ethyl (2 carbons) = 5 carbons in the product alcohol.
Ketone + Grignard \(\rightarrow\) Tertiary alcohol.
Only option (C) fits a 5-carbon tertiary alcohol structure.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The reaction involves the addition of a Grignard reagent (ethyl magnesium bromide) to a ketone (acetone), followed by acidic hydrolysis.

Step 2: Key Formula or Approach:
Reaction of a ketone with a Grignard reagent yields a tertiary alcohol.
Nucleophilic addition of the ethyl group (\(\text{C}_{2}\text{H}_{5}^{-}\)) to the carbonyl carbon of acetone occurs first.

Step 3: Detailed Explanation:
Structure of Acetone: \(\text{CH}_{3}-\text{C}(=\text{O})-\text{CH}_{3}\)
Step (i): Addition of \(\text{C}_{2}\text{H}_{5}\text{MgBr}\)
The \(\text{C}_{2}\text{H}_{5}\) group attacks the central carbon of acetone.
Intermediate: \(\text{CH}_{3}-\text{C}(\text{OMgBr})(\text{C}_{2}\text{H}_{5})-\text{CH}_{3}\)
Step (ii): Hydrolysis with \(\text{H}_{2}\text{O, H}^{+}\)
The \(\text{OMgBr}\) group is converted to \(\text{OH}\).
Final Product: \(\text{CH}_{3}-\text{C}(\text{OH})(\text{CH}_{3})-\text{CH}_{2}-\text{CH}_{3}\)
Determining IUPAC Name:
1. Longest carbon chain containing the \(\text{OH}\) group: 4 carbons (Butane).
2. Numbering from the end closer to \(\text{OH}\): \(\text{C}_{1}\) is \(\text{CH}_{3}\), \(\text{C}_{2}\) has \(\text{OH}\) and a methyl group.
Name: 2-methylbutan-2-ol.

Step 4: Final Answer:
The correct IUPAC name is 2-methyl butan-2-ol.