Question

Which of the following compounds does NOT exhibit optical isomerism?

• A. 2-Iodo-3-methylbutane
• B. 3-Iodohexane
• C. 2-Iodopentane
• D. 2-Iodo-2-methylbutane

Hint:

Any name featuring identical numbers for two distinct groups at the same position (such as 2-Iodo-2-methyl...) indicates that two positions on that carbon are occupied by methyl paths, ensuring the carbon is achiral.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We need to determine which of the given alkyl iodides lacks optical activity by checking for the absence of an asymmetric chiral carbon center.

Step 2: Detailed Explanation:
A molecule displays optical isomerism if it contains at least one chiral carbon atom—a tetrahedral carbon bonded to four entirely different atoms or groups. Let's inspect the structures:

2-Iodo-3-methylbutane: $\text{CH}_3\text{-C}^* \text{H(I)-CH(CH}_3)_2$. The $\text{C}_2$ carbon is chiral because it connects to -H, -I, $\text{-CH}_3$, and $\text{-CH(CH}_3)_2$.

3-Iodohexane: $\text{CH}_3\text{-CH}_2\text{-C}^* \text{H(I)-CH}_2\text{-CH}_2\text{-CH}_3$. The $\text{C}_3$ carbon is chiral as it binds to -H, -I, $\text{-C}_2\text{H}_5$, and $\text{-C}_3\text{H}_7$.

2-Iodopentane: $\text{CH}_3\text{-C}^* \text{H(I)-CH}_2\text{-CH}_2\text{-CH}_3$. The $\text{C}_2$ carbon is chiral since it binds to -H, -I, $\text{-CH}_3$, and $\text{-C}_3\text{H}_7$.

2-Iodo-2-methylbutane: $\text{CH}_3\text{-C(I)(CH}_3)\text{-CH}_2\text{-CH}_3$. The $\text{C}_2$ carbon is bonded to an iodine atom, an ethyl group, and

two identical methyl groups.
Because it has two identical methyl groups attached to the central carbon, 2-Iodo-2-methylbutane lacks a chiral center and cannot exhibit optical isomerism.

Step 3: Final Answer: The compound that does not show optical activity is option (D).