Carboxylic Acids and their Derivatives - Result Question 38

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

$$ Q \xrightarrow[\Delta]{H _2 / Ni} V $$

(a)

$(V)$

$(W)$

(b)

and

$(V)$

$(W)$ (c)

(d)

$(V)$

$(W)$

Passage 3

$R CONH _2$ is converted into $R NH _2$ by means of Hofmann’s bromamide degradation.

(i)

(ii)

(v)

(vi)

In this reaction, $R CONHBr$ 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. $\quad(2006,3 \times 4 M=12 M)$

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Solution:

  1. PLAN Ikenes decolourise $Br _2$ water

$$ \begin{gathered} \text {-isomer } \xrightarrow{\text { dil } \cdot KMnO _4} \quad \text { isomers by } \quad \text { addition } \ \text {-isomer } \xrightarrow{\text { dil } \cdot KMnO _4} d(+) \text { and } l(-) \text { isomers by } \end{gathered} $$

Formation of anhydride from dicarboxylic acid indicates -isomer.

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

$P, Q \xrightarrow{Br _2 \text { water }}$ decolourised

$P$ and $Q$ have $(C=C)$ 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.



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