Chemistry Q65 – JEE-MAIN 2025

Home Chemistry Basic Organic ChemistryQuestion #160

In 3,3-dimethylhex-1-en-4-yne, there are _______

s p^{3}

, _______

s p^{2}

and _______

s p

hybridised carbon atoms respectively.

Clue 1 of 3: Molecular Structure

Start by drawing the correct structural formula of the given organic compound.

🧠 Full Solution Path

Step 1: Draw the structure of 3,3-dimethylhex-1-en-4-yne✦ Active

The name indicates a 6-carbon main chain (hex) with a double bond at C1 (-en) and a triple bond at C4 (-yne). Two methyl groups are attached to C3. The structure is:

\begin{matrix} {CH}_{3} \\ | \\ {CH}_{2} = CH - C - C \equiv C - {CH}_{3} \\ | \\ {CH}_{3} \end{matrix}

💡 Teacher's Secret Hint

Pay close attention to the numbering and placement of substituents and multiple bonds.

Step 2: Determine the hybridization of each carbon atom○ Expand

Hybridization is determined by the number of sigma bonds and lone pairs around a carbon atom. For carbon, 4 sigma bonds means $s p^{3}$ , 3 sigma bonds means $s p^{2}$ , and 2 sigma bonds means $s p$ .

1. $C_{1}$ ( $C H_{2} =$ ): Forms 1 double bond and 2 single bonds to H. Total 3 sigma bonds $\to s p^{2}$ . 2. $C_{2}$ ( $= C H -$ ): Forms 1 double bond, 1 single bond to H, and 1 single bond to $C_{3}$ . Total 3 sigma bonds $\to s p^{2}$ . 3. $C_{3}$ ( $- C (C H_{3})_{2} -$ ): Forms 4 single bonds (to $C_{2}$ , $C_{4}$ , and two methyl carbons). Total 4 sigma bonds $\to s p^{3}$ . 4. Methyl carbons ( $C H_{3}$ ) attached to $C_{3}$ : Each forms 1 single bond to $C_{3}$ and 3 single bonds to H. Total 4 sigma bonds $\to s p^{3}$ . (There are two such carbons). 5. $C_{4}$ ( $- C \equiv$ ): Forms 1 triple bond and 1 single bond to $C_{3}$ . Total 2 sigma bonds $\to s p$ . 6. $C_{5}$ ( $\equiv C -$ ): Forms 1 triple bond and 1 single bond to $C_{6}$ . Total 2 sigma bonds $\to s p$ . 7. $C_{6}$ ( $- C H_{3}$ ): Forms 1 single bond to $C_{5}$ and 3 single bonds to H. Total 4 sigma bonds $\to s p^{3}$ .

💡 Teacher's Secret Hint

Remember that a double bond contains one sigma and one pi bond, and a triple bond contains one sigma and two pi bonds. Hybridization considers only sigma bonds.

Step 3: Count the number of

s p^{3}

s p^{2}

, and

s p

hybridized carbon atoms○ Expand

Based on the hybridization determined in Step 2:

- Number of $s p^{3}$ carbons: $C_{3}$ , $C_{3}$ -methyl (top), $C_{3}$ -methyl (bottom), $C_{6}$ = 4 - Number of $s p^{2}$ carbons: $C_{1}$ , $C_{2}$ = 2 - Number of $s p$ carbons: $C_{4}$ , $C_{5}$ = 2

Thus, there are 4 $s p^{3}$ , 2 $s p^{2}$ , and 2 $s p$ hybridized carbon atoms respectively.

💡 Teacher's Secret Hint

Double-check your count to avoid simple arithmetic errors.

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Chemistry Question 65 – JEE-MAIN 2025

Clue 1 of 3: Molecular Structure

🧠 Full Solution Path