Question 5.SSE.7: An organic compound containing C. H and O exists in two isom......
An organic compound containing C. H and O exists in two isomeric forms A and B. An amount of 0.108 g of one of the isomers gives on combustion 0.308 g of CO_2 in 0.072 g of H_2O . A is insoluble in NaOH and NaHCO_3 while B is soluble in NaOH . A reacts with cone. HI to give compounds C and D. C can be separated from D by the ethanolic AgNO_3 solution and D is soluble in NaOH . B reacts readily with bromine water to give compound E of molecular formula, C_7H_5OBr_3 . Identify, A, B, C, D and E with justification and give their structures.
[IIT, 1991]
(i) For empirical formula of (A)
\begin{matrix} \text {Element} & \text {Percentage} & \text { Relative no. of atoms }=\% / \text { at. mass } & \text {Simplest ratio} \\\\ C & \frac{12}{44} \times \frac{0.308}{0.108} \times 100=77.77 & \frac{77.77}{12}=6.46 & 7 \\\\ H & \frac{2}{18} \times \frac{0.072}{0.108} \times 100=7.40 & \frac{7.40}{1}=7.40 & 8 \\O & 100-(77.77+7.40) = 14.83 & \frac{14.83}{16}=0.93 & 1 \end{matrix}
So the empirical formula of (A)= C _7 H _8 O
(ii) As (B) gives C _7 H _5 OBr _3 and (B) is isomer of (A), so molecular formula of (A) and (B) is C _7 H _8 O \text {. }
(iii) As (A) is insoluble in NaOH and NaHCO_3 so
(A) is 
(iv) (A) is also confirmed by action with HI .
\begin{matrix} + & HI & \longrightarrow \\\\\\\\\\\\ \end{matrix} 
\begin{matrix} +& CH_3I \\ & \text {(C)} \\ & \text{Soluble in} \\ & AgNO_3 \\\\\\ \end{matrix}
(v) 
i.e., m-cresol since only.
(B) is soluble in NaOH and gives (E) \left( C _7 H _5 OBr _3\right) with Br_2 water,so (B) is
\begin{matrix} \overset{Br _2 \text { water }}{\xrightarrow {\hspace{2 cm}} } \\\\\\\\\\\\ \end{matrix} 
meta-position can provide tribromo derivative.