Question

a) Give resonating structure of carboxylic group?
b) Give chemical reaction to obtain the following.
i) Carboxylic acid from Grignard reagent.
ii) Benzoic acid from ethyl benzoate.
iii) Benzamide from benzoic acid.
c) Give resonating structures of propenoic acid?
d) How will you distinguish aldehyde, ketone & carboxylic acid.

Answer 1

a) The resonating structure of carboxylic group are as shown.
b) Chemical reaction to obtain the following.
i) Carboxylic acid from Grignard reagent.
$R-MgX+C{O}_2\to R-COO-MgX\stackrel{H_{2}O}{\to }R-COOH+Mg\left(OH\right)X$
ii) Benzoic acid from ethyl benzoate.
$PhCOOEt\underset{-EtOH}{\overset{NaOH}{\to }}PhCOONa\underset{-NaCl}{\overset{HCl}{\to }}PhCOOH$
iii) Benzamide from benzoic acid.
$PhCOOH+N{H}_3\rightleftharpoons PhCO{O}^{-}N{H}_4^{+}\stackrel{\Delta }{\to }PhCON{H}_2+H_{2}O$
c) The resonating structures of propenoic acid are as shown.
d) To distinguish aldehyde, ketone & carboxylic acid:
Carboxylic acid will give effervescence with sodium hydrogen carbonate.
Aldehdye will give positive test with Tollen's reagent (ammoniacal silver nitrate solution) which will produce silver mirror.
The remaining compound will be ketone.