See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Structural Isomers of $C_5H_{10}$ **Step 1: Determine degree of unsaturation** $$\text{DBE} = \frac{2(5) + 2 - 10}{2} = \frac{2}{2} = 1$$ One degree of unsaturation means either **one double bond OR one ring**. **Step 2: Enumerate alkene isomers (C=C double bond)** - Pent-1-ene: $CH_2=CH-CH_2-CH_2-CH_3$ - Pent-2-ene: $CH_3-CH=CH-CH_2-CH_3$ (cis and trans are stereoisomers, not structural) - 2-methylbut-1-ene: $CH_2=C(CH_3)-CH_2-CH_3$ - 3-methylbut-1-ene: $CH_2=CH-CH(CH_3)-CH_3$ - 2-methylbut-2-ene: $CH_3-C(CH_3)=CH-CH_3$ **Total alkenes: 5 isomers** **Step 3: Enumerate cycloalkane isomers (rings)** - Cyclopentane: five-membered ring - Methylcyclobutane: four-membered ring with methyl substituent - Ethylcyclopropane: three-membered ring with ethyl substituent - 1,1-dimethylcyclopropane: two methyls on same carbon - 1,2-dimethylcyclopropane: two methyls on adjacent carbons **Total cycloalkanes: 7 isomers** **Step 4: Total count** $$5 + 7 = \boxed{12 \text{ structural isomers}}$$ **Answer: (C) 12**