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:
- 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.
