Carboxylic Acids and their Derivatives 2 Question 23

24. In the following reaction sequences $V$ and $W$ are respectively

$$ Q \xrightarrow[\Delta]{\mathrm{H}_{2} / \mathrm{Ni}} V $$

(a)

$(V)$

$(W)$

(b)

and

$(V)$

$(W)$ (c)

(d)

$(V)$

$(W)$

Passage 3

$R \mathrm{CONH}{2}$ is converted into $R \mathrm{NH}{2}$ by means of Hofmann’s bromamide degradation.

(i)

(ii)

(v)

(vi)

In this reaction, $R \mathrm{CONHBr}$ is formed from which this reaction has derived its name. Electron donating group at phenyl activates the reaction. Hofmann’s degradation reaction is an intramolecular reaction. $\quad(2006,3 \times 4 \mathrm{M}=12 \mathrm{M})$

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Solution:

  1. PLAN Ikenes decolourise $\mathrm{Br}_{2}$ water

$$ \begin{gathered} \text {-isomer } \xrightarrow{\text { dil } \cdot \mathrm{KMnO}{4}} \quad \text { isomers by } \quad \text { addition } \ \text {-isomer } \xrightarrow{\text { dil } \cdot \mathrm{KMnO}{4}} d(+) \text { and } l(-) \text { isomers by } \end{gathered} $$

Formation of anhydride from dicarboxylic acid indicates -isomer.

$P$ and $Q$ are isomers of dicarboxylic acids.

$P, Q \xrightarrow{\mathrm{Br}_{2} \text { water }}$ decolourised

$P$ and $Q$ have $(\mathrm{C}=\mathrm{C})$ bond

$$ P \stackrel{\Delta}{\longrightarrow} \text { anhydride } $$

Thus, $P$ is cis-isomer.

$(P)$

(maleic acid)

$(S)$

Optically inactive due to internal compensation of rotation (meso-isomer) (fumaric acid)

(T) $d(+)$

$(U) l(-)$ $T$ and $U$ (in 1: 1 molar ratio) form optically inactive (racemic mixture) due to external compensation.