Question

Organic compound $C_5H_{10}$ does not give Baeyer’s reagent test. Calculate total number of structural monobromo isomers when react with $Br_2/h\nu$.

Answer 1

Baeyer's reagent test is used to detect unsaturation (alkenes/alkynes). If $C_5H_{10}$ (degree of unsaturation = 1) does not give this test, it must be a saturated cyclic compound (cycloalkane).
1. Identify the possible cycloalkane isomers of $C_5H_{10}$:
• Cyclopentane
• Methylcyclobutane
• Ethylcyclopropane
• 1,1-Dimethylcyclopropane
• 1,2-Dimethylcyclopropane

2. Calculate monobromo structural isomers for each:
• Cyclopentane: All hydrogens are equivalent. Only 1 isomer.
• Methylcyclobutane: Has 4 types of carbons. 4 isomers.
• Ethylcyclopropane: Has 4 types of carbons (primary of ethyl, secondary of ethyl, tertiary of ring, secondary of ring). 4 isomers.
• 1,1-Dimethylcyclopropane: Has 2 types of carbons (methyls and ring methylene). 2 isomers.
• 1,2-Dimethylcyclopropane: Has 3 types of structural positions (methyl, ring methine, ring methylene). 3 isomers.

3. Summation:
Total structural isomers = $1 + 4 + 4 + 2 + 3 = 14$.

The answer is 14.