Question

Which of the following on reactions with nitrous acid, followed by treatment with $NaOH$ produces a blue coluration?

• A. $RC{H}_{2}N{O}_2$
• B. $R_{3}CN{O}_2$
• C. $R_{2}CHN{O}_2$
• D. $PhN{O}_2$

Answer 1

Answer: (C)

$R-\underset{N{O}_2}{\underset{|}{C}{H}_2}+O=N-OH\to \underset{\underset{\underset{\text{blood red colouration}}{\text{Dissolve in NaOH to give}}}{\left(\text{Nitrolic acid}\right)}}{R-\underset{N{O}_2}{\underset{|}{C}=N}-OH+H_{2}O}$
$R-\underset{N{O}_2}{\stackrel{R}{\stackrel{|}{\underset{|}{C}}}-R}+HN{O}_2\to$ No reaction
$\text{R}-\underset{{\left(\text{NO}\right)}_{\text{2 }}}{\stackrel{\text{R}}{\stackrel{\text{|}}{\underset{\text{|}}{C}}}-\text{H}}+\text{HO}-\text{N}=\text{O}\to \underset{\underset{\underset{\text{but gives blue colouration}}{\text{Does not dissolve in NaOH,}}}{\left(\text{Pseudo}\text{nitrole}\right)}}{\text{R}-\underset{{\left(\text{NO}\right)}_{\text{2}}}{\stackrel{\text{R}}{\stackrel{\text{|}}{\underset{\text{|}}{C}}}-\text{N}}=\text{O}+{\left(\text{H}\right)}_{\text{2}}\text{O}}$
$PhN{O}_2+HN{O}_2\to$ No reaction