Question

Incorrect method of preparation for alcohols from the following is:

• A. Hydroboration-oxidation of alkene.
• B. Reaction of Ketone with RMgBr followed by hydrolysis.
• C. Reaction of alkyl halide with aqueous NaOH.
• D. Ozonolysis of alkene.

Answer 1

The Correct Option is D

Step 1: Understanding the methods of alcohol preparation.
Let's evaluate each of the methods:
1. Ozonolysis of alkene:
Ozonolysis involves the cleavage of the double bond in an alkene using ozone (O\(_3\)) to form two carbonyl compounds, which could be either aldehydes or ketones.
The reaction proceeds as: \[ \text{CH}_2=\text{CH}_2 \xrightarrow{\text{O}_3} \text{C}=\text{O} + \text{C}=\text{O} \] This is a two-step reaction that involves the addition of borane (BH\(_3\)) to an alkene, followed by oxidation to form an alcohol. 2. Hydroboration-oxidation of alkene:
This is a two-step reaction that involves the addition of borane (BH\(_3\)) to an alkene, followed by oxidation to form an alcohol.
The reaction proceeds as:
\[ \text{CH}_2=\text{CH}_2 + \text{BH}_3 \xrightarrow{\text{Zn, H}_2\text{O}} \text{CH}_3\text{CH}_2\text{OH} \] This method is correct for preparing alcohols from alkenes, and it follows the syn addition of boron and hydrogen across the double bond, followed by the formation of an alcohol after oxidation.
3. Reaction of alkyl halide with aqueous NaOH:
This is a nucleophilic substitution reaction, where an alkyl halide reacts with aqueous NaOH to form an alcohol.
The reaction proceeds as: \[ \text{R-X} + \text{NaOH} \rightarrow \text{R-OH} + \text{NaX} \] This is a correct method for alcohol preparation, as the hydroxide ion acts as a nucleophile and displaces the halide ion to form an alcohol.
4. Reaction of Ketone with RMgBr followed by hydrolysis:
This is a reaction of a ketone with a Grignard reagent (RMgBr), which adds to the carbonyl carbon, followed by hydrolysis to form an alcohol.
The reaction proceeds as: \[ \text{R}_2\text{C}= \text{O} + \text{RMgBr} \xrightarrow{\text{H}_2\text{O}} \text{R}_2\text{C(OH)R} \] This is a correct method for preparing alcohols, specifically secondary alcohols, from ketones.
Thus, the only incorrect method for preparing alcohols is ozonolysis of alkene.