Question

Identify the unknowns in the following reaction sequence.

(P) (Hydrocarbon) $\xrightarrow{Na/liq.NH_3}$ (Q) $\xrightarrow[\text{H}_2\text{O}]{\text{O}_3}$ 2(R) $\xrightarrow{\triangle}$ 2CH$_3$COOH + 2CO$_2$

• A. (Q) =

  , (P) =

• B. (P) =

  , (Q) =

• C. (Q) =

  , (P) = $CH_2 \begin{matrix} COOH \\ | \\ COOH \end{matrix}$

• D. (Q) =

  , (R) = $\begin{matrix} CH_2-COOH \\ | \\ CH_2-COOH \end{matrix}$

Answer 1

Answer: (B)

(P) = Benzene, (Q) = 1,4-Cyclohexadiene

Answer 2

The reaction sequence is analyzed step by step. The last step, heating of (R) to give acetic acid and carbon dioxide, indicates that (R) is malonic acid. The ozonolysis of (Q) to give two molecules of malonic acid suggests that (Q) is 1,4-cyclohexadiene, which upon ozonolysis cleaves into two fragments of malonic acid. The reaction of (P) with Na/liq. NH$_3$ to give (Q) is a Birch reduction, which reduces benzene to 1,4-cyclohexadiene. Therefore, (P) is benzene.