Question

An organic compound (A) with molecular formula $C_8H_8O$ gives positive Brac with chromic acid gives a compound (B) which on reduction with Red P/HI g a compound (D) which is used in explosives. The number of $\pi$ bonds in (D) is

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (C)

3

Answer 2

The molecular formula of compound (A) is $C_8H_8O$. The degree of unsaturation is 5. A positive test with chromic acid suggests an aldehyde or primary/secondary alcohol. A likely structure for (A) is Phenylacetaldehyde ($C_6H_5-CH_2-CHO$). Oxidation of (A) with chromic acid yields Phenylacetic acid (B) ($C_6H_5-CH_2-COOH$). Reduction of (B) with Red P/HI converts the carboxylic acid to a methyl group, forming Toluene (D) ($C_6H_5-CH_3$). Toluene is a precursor to TNT, an explosive. Toluene has 3 $\pi$ bonds in its benzene ring.