See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Finding Functional Isomers of 1-Butyne **Step 1: Identify the reference compound** 1-Butyne is $HC\equiv C-CH_2-CH_3$ (molecular formula: $C_4H_6$) **Step 2: Check molecular formula of each option** - (1) $CH_3-C\equiv C-CH_3$ → $C_4H_6$ ✓ - (2) $CH_3-C(=CH_2)-CH_3$ → $C_5H_{10}$ ✗ (has 5 carbons) - (3) $CH_2=CH-CH=CH_2$ → $C_4H_6$ ✓ - (4) $CH_2=CH-CH=CH_2$ → $C_4H_6$ ✓ **Step 3: Eliminate incorrect options** Option (2) has 5 carbons, so it's not an isomer of 1-butyne ($C_4H_6$). This eliminates choices A, B, and C. **Step 4: Verify compounds (3) and (4) are functional isomers** - (3) $CH_2=CH-CH=CH_2$ is **1,3-butadiene** (two C=C double bonds) - (4) is the same structure: $CH_2=CH-CH=CH_2$ (conjugated diene) Both represent the same compound with different functional groups (diene) compared to 1-butyne (alkyne). **Answer: (D) (3) and (4) only** *Note: (3) and (4) represent the same compound, 1,3-butadiene, which is a functional isomer of 1-butyne.*