The Question is from neet-chemistry organic-chemistry-basics isomerism-structural-and-stereo, and it was created by the author P SRAVAN KUMAR

Question

A compound with the molecular formula $C_6H_{12}O_2$ shows optical activity but no geometrical isomerism. Which of the following could be the compound?

P SRAVAN KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Stereochemistry (Optical isomerism and geometrical isomerism)
 **Related Topics**: Organic functional groups, molecular structure
 **Prerequisites**: Understanding of chirality, $sp^2$ and $sp^3$ hybridized carbons, and functional groups like carboxylic acids and esters.
## SOLUTION PATHWAY
**Given Information**:
  Molecular formula: $C_6H_{12}O_2$
  Shows optical activity (presence of chiral center)
  No geometrical isomerism (absence of $C=C$ double bonds or other structures allowing cis-trans isomerism)
**Method & Steps**:
 1. Analyze each option for chirality and geometrical isomerism.
  Reasoning: Optical activity requires a chiral center (a carbon atom with four different substituents). Geometrical isomerism requires a restricted rotation around a bond, usually a double bond.
 2. Evaluate the structures of the given options.
  Working:
  A. Hex-3-en-2-one: Contains a $C=C$ double bond, allowing geometrical isomerism.  It also has a chiral center.
  B. 2,3-dimethylbut-2-enoic acid: Contains a $C=C$ double bond, thus exhibiting geometrical isomerism.
  C. Ethyl 2-methylpropanoate: This is an ester; it does not contain any chiral centers.
  D. 2-hydroxy-4-methylpentanoic acid: This is a chiral molecule with a chiral carbon at position 2. It does not contain any $C=C$ double bonds. 
  Key Point: The presence of a hydroxyl group (-OH) and a carboxyl group (-COOH) on the same carbon can also lead to optical activity, although less common.
 3. Identify the compound fulfilling both conditions.
  Result: Only 2-hydroxy-4-methylpentanoic acid (option D) shows optical activity due to the chiral carbon and lacks geometrical isomerism because it has no $C=C$ double bonds.
  Verification: The structure of option D satisfies the given criteria.
 ## OPTION ANALYSIS
A :x:  Hex-3-en-2-one has a $C=C$ double bond, thus it exhibits geometrical isomerism.
B :x: 2,3-dimethylbut-2-enoic acid has a $C=C$ double bond, thus it exhibits geometrical isomerism.
C :x: Ethyl 2-methylpropanoate has no chiral center, hence no optical activity.
D ✓: 2-hydroxy-4-methylpentanoic acid has a chiral center (optical activity) and no $C=C$ double bond (no geometrical isomerism).
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing optical and geometrical isomerism: Remember that optical isomerism arises from chirality, while geometrical isomerism arises from restricted rotation around a bond.
  2.Overlooking the possibility of multiple chiral centers: A molecule can have more than one chiral center.
 **Quick Tips**:
  1.Look for chiral carbons (carbons with four different substituents) to identify optical activity.
  2.Check for $C=C$ double bonds or other structural features that restrict rotation to identify geometrical isomerism.

P SRAVAN KUMAR · Answer

Hex-3-en-2-one

P SRAVAN KUMAR · Answer

2,3-dimethylbut-2-enoic acid

P SRAVAN KUMAR · Answer

Ethyl 2-methylpropanoate

P SRAVAN KUMAR · Answer

The correct Option is "2-hydroxy-4-methylpentanoic acid"

NEET Chemistry Organic Chemistry: Some basic principles and techniques Isomerism [Structural & Stereo] MCQs

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