Incorrect method of preparation for alcohols from the following is:

Hydroboration-oxidation of alkene.

Reaction of Ketone with RMgBr followed by hydrolysis.

Reaction of alkyl halide with aqueous NaOH .

Alcohols Phenols and Ethers PYQ — JEE Main 2023 · 10 Apr · Shift 2 · Q8 with Solution

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Correct answer: C

We need to identify the incorrect method for preparation of alcohols.
Check each option:

A. Hydroboration–oxidation of alkene
This is a standard method to prepare alcohols from alkenes: $\text{Alkene} \xrightarrow[2.\,H_2O_2/OH^-]{1.\,BH_3} \text{Alcohol}$ Hence, A is correct as a method of alcohol preparation.

B. Reaction of ketone with $\mathrm{RMgBr}$ followed by hydrolysis
Grignard reagent adds to ketones to give alkoxides, which on hydrolysis form alcohols: $R_2C=O + RMgBr \rightarrow R_2C(OMgBr)R \xrightarrow{H_3O^+} R_2C(OH)R$ This gives a tertiary alcohol. Hence, B is correct.

C. Ozonolysis of alkene
Ozonolysis cleaves the double bond and generally gives aldehydes, ketones, or carboxylic acids depending on workup, not alcohols: $RCH=CHR' \xrightarrow{O_3} \text{carbonyl compounds}$ Hence, C is not a method of preparing alcohols.

D. Reaction of alkyl halide with aqueous $\mathrm{NaOH}$
Nucleophilic substitution of alkyl halide with aqueous sodium hydroxide gives alcohol: $R-X + NaOH_{(aq)} \rightarrow R-OH + NaX$ Hence, D is correct.
Therefore, the incorrect method is: $\boxed{\text{C}}$
Comparison with stored correct answer: stored answer is C, which matches our derived answer.

View written solutionFree

Correct answer: C

We need to identify the incorrect method for preparation of alcohols.
Check each option:

A. Hydroboration–oxidation of alkene
This is a standard method to prepare alcohols from alkenes: $\text{Alkene} \xrightarrow[2.\,H_2O_2/OH^-]{1.\,BH_3} \text{Alcohol}$ Hence, A is correct as a method of alcohol preparation.

B. Reaction of ketone with $\mathrm{RMgBr}$ followed by hydrolysis
Grignard reagent adds to ketones to give alkoxides, which on hydrolysis form alcohols: $R_2C=O + RMgBr \rightarrow R_2C(OMgBr)R \xrightarrow{H_3O^+} R_2C(OH)R$ This gives a tertiary alcohol. Hence, B is correct.

C. Ozonolysis of alkene
Ozonolysis cleaves the double bond and generally gives aldehydes, ketones, or carboxylic acids depending on workup, not alcohols: $RCH=CHR' \xrightarrow{O_3} \text{carbonyl compounds}$ Hence, C is not a method of preparing alcohols.

D. Reaction of alkyl halide with aqueous $\mathrm{NaOH}$
Nucleophilic substitution of alkyl halide with aqueous sodium hydroxide gives alcohol: $R-X + NaOH_{(aq)} \rightarrow R-OH + NaX$ Hence, D is correct.
Therefore, the incorrect method is: $\boxed{\text{C}}$
Comparison with stored correct answer: stored answer is C, which matches our derived answer.