Question

Identify the major product from the following reaction sequence 
 

 

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

Grignard reagents add alkyl groups to carbonyl compounds. Ketones give tertiary alcohols, which on acid-catalysed dehydration form alkenes as major products.

Answer 1

The Correct Option is C

Step 1: Reaction with Grignard reagent.
The given compound contains a ketonic carbonyl group.
Methyl magnesium chloride, \[ CH_3MgCl \] acts as a source of nucleophilic methyl group: \[ CH_3^- \] It attacks the carbonyl carbon and forms an alkoxide intermediate.

Step 2: Acid hydrolysis.
On hydrolysis with \[ H_3O^+ \] the alkoxide intermediate is converted into a tertiary alcohol.
Thus, the first major intermediate is a tertiary alcohol.

Step 3: Dehydration of tertiary alcohol.
On heating with \[ 20\%\,H_3PO_4 \] at \[ 358\,K \] the tertiary alcohol undergoes acid-catalysed dehydration.
A molecule of water is eliminated and an alkene is formed.

Step 4: Formation of major alkene.
The dehydration proceeds through a carbocation intermediate.
The more stable alkene is formed as the major product according to Saytzeff rule, along with stability due to the substituted ring system.
Among the given options, this corresponds to option (3).

Step 5: Final conclusion.
Therefore, the major product is \[ \boxed{\text{Option (3)}} \]