See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Stereoisomerism Analysis **Understanding Stereoisomerism Requirements:** Stereoisomerism (specifically geometric/cis-trans or optical isomerism) requires: - For alkenes: different groups on both carbons of the C=C bond - For saturated compounds: a chiral center (carbon with 4 different groups) **Analyzing Each Option:** **(A) 2-methylbutene-1:** $CH_2=CH-CH(CH_3)-CH_3$ - Terminal C=C has two H atoms on one carbon - Cannot show cis-trans isomerism ✗ **(B) 3-methylbutene-1:** $CH_2=CH-CH_2-CH(CH_3)_2$ - Terminal C=C has two H atoms on one carbon - Cannot show cis-trans isomerism ✗ **(C) 3-methylbutanoic acid:** $CH_3-CH(CH_3)-CH_2-COOH$ - Carbon bearing methyl group: attached to $H, CH_3, CH_2COOH, CH_3$ - Has one chiral center but **no stereoisomerism with the carboxylic acid** (no E/Z on C=O) - Would show optical isomerism (D/L forms) but not the typical "stereoisomerism" in structural sense ✗ **(D) 2-methylbutanoic acid:** $CH_3-CH_2-CH(CH_3)-COOH$ - The carbon at position 2 (α-carbon) has: $H, CH_3, CH_2CH_3, COOH$ — four **different groups** - This is a true **chiral center** exhibiting optical isomerism (cis-trans or R/S configuration) - Exists as D and L enantiomers ✓ **Answer: (D) 2-methylbutanoic acid** — possesses a chiral center with four different substituents, exhibiting optical stereoisomerism.