Carboxylic Acids and their Derivatives 2 Question 24
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:
- 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.
