Question

An optically active alkene having molecular formula C$_8$H$_{16}$ gives acetone as one of the products on ozonolysis. The structure of the alkene is

• A.
• B.
• C.
• D.

Hint:

Using a simple frame or just bolding for the box Key Points: Ozonolysis: Cleaves C=C double bonds. $R_1R_2$C=CR$_3R_4 \xrightarrow{\text{O_3; \text{reductive workup R_1R_2$C=O + O=CR$_3R_4$. To yield acetone (CH$_3$COCH$_3$), one side of the alkene must be =C(CH$_3$)$_2$. Optical Activity: Requires the molecule to be chiral (non-superimposable on its mirror image). Usually presence of one or more chiral centers (carbon atom bonded to four different groups) and lack of internal symmetry planes. Molecular Formula: Check if the sum of carbons and hydrogens matches the given formula (C$_n$H$_{2n$ for simple alkenes).

Answer 1

The Correct Option is B

The task is to identify an alkene meeting three criteria:\n\n(A) Molecular formula: C₈H₁₆.\n(B) Produces acetone (CH₃COCH₃) via ozonolysis.\n(C) Optically active (possesses a chiral center, excluding meso compounds).\n\nLet's examine the options:\n\n

\n
• (A) 2,3-Dimethylhex-2-ene:
  \n Formula: C₈H₁₆ (Matches).
  \n Ozonolysis: The double bond cleavage yields acetone and 2-pentanone. Acetone is produced.
  \n Optical Activity: No chiral center. Optically inactive.
\n
• (B) 3,4-Dimethylhex-2-ene:
  \n Formula: C₈H₁₆ (Matches).
  \n Ozonolysis: The double bond cleavage yields acetone and 3-methylpentan-2-al. Acetone is produced.
  \n Optical Activity: C4 has four distinct groups: H, CH₃, C₂H₅, and the alkene group; it is a chiral center. The molecule is optically active.
\n
• (C) 3,4-Dimethylhex-3-ene:
  \n Formula: C₈H₁₆ (Matches).
  \n Ozonolysis: The double bond cleavage yields propanal and 3-methylbutan-2-one. Does not yield acetone.
\n
• (D) 3-Ethyl-2-methylpent-2-ene:
  \n Formula: C₈H₁₆ (Matches).
  \n Ozonolysis: The double bond cleavage yields acetone and 3-pentanone. Acetone is produced.
  \n Optical Activity: No chiral center. Optically inactive.
\n

\n\nOnly option (B) fulfills all requirements: formula C₈H₁₆, acetone production via ozonolysis, and optical activity due to a chiral center at C4.\n\n