Chemistry Q72 – JEE-MAIN 2026

Home Chemistry Basic Organic ChemistryQuestion #134

'x' is the product which is obtained from benzene by reacting it with carbon monoxide and hydrogen chloride in the presence of cuprous chloride. 'y' is the major product obtained from the benzene by reacting it with ethanoyl chloride in the presence of anhydrous

A l C l_{3}

. Product (major) obtained by heating

x

and

y

in the presence of alkali is

z

. Total number of

π

(pi) electrons in

z

is _______.

Enter Calculated Numerical Value:

Clue 1 of 3: Identify the reactions

The first reaction is Gattermann-Koch synthesis, and the second is Friedel-Crafts acylation.

🧠 Full Solution Path

Step 1: Identify compounds 'x' and 'y'✦ Active

Compound 'x' is obtained from benzene by reacting it with carbon monoxide and hydrogen chloride in the presence of cuprous chloride ( $C u C l$ ). This is the Gattermann-Koch reaction, which yields benzaldehyde.

Benzene \overset{C O, H C l, C u C l}{\to} Benzaldehyde (x) (C_{6} H_{5} C H O)

Compound 'y' is obtained from benzene by reacting it with ethanoyl chloride ( $C H_{3} C O C l$ ) in the presence of anhydrous $A l C l_{3}$ . This is a Friedel-Crafts acylation reaction, which yields acetophenone.

Benzene \overset{C H_{3} C O C l, A n h y d r o u s A l C l_{3}}{\to} Acetophenone (y) (C_{6} H_{5} C O C H_{3})

Step 2: Identify compound 'z'○ Expand

Compound 'z' is the major product obtained by heating 'x' (Benzaldehyde) and 'y' (Acetophenone) in the presence of alkali. Benzaldehyde has no $α$ -hydrogens, while acetophenone has $α$ -hydrogens. This reaction is a Claisen-Schmidt condensation (a type of Aldol condensation).

C_{6} H_{5} C H O + C H_{3} C O C_{6} H_{5} \overset{O H^{-}, Δ}{\to} C_{6} H_{5} - C H = C H - C O - C_{6} H_{5} + H_{2} O

So, 'z' is Chalcone (1,3-diphenylprop-2-en-1-one).

Step 3: Count the total number of

π

electrons in 'z'○ Expand

The structure of Chalcone ( $C_{6} H_{5} - C H = C H - C O - C_{6} H_{5}$ ) contains:

1. Two benzene rings: Each benzene ring has 3 double bonds, contributing $3 \times 2 = 6$ $π$ electrons. So, two rings contribute $2 \times 6 = 12$ $π$ electrons.

2. One $C = C$ double bond in the aliphatic chain: This contributes 2 $π$ electrons.

3. One $C = O$ double bond (ketone group): This contributes 2 $π$ electrons.

Total number of $π$ electrons in 'z' = $12 + 2 + 2 = 16$ .

💡 Teacher's Secret Hint

Remember to count pi electrons from all double bonds, including those within aromatic rings and carbonyl groups.

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Chemistry Question 72 – JEE-MAIN 2026

Clue 1 of 3: Identify the reactions

🧠 Full Solution Path