Chemistry CUET UG 22-05-2023 Shift 3 Paper

The reduction half-reaction of permanganate ion to manganese(II) ion in acidic medium is:

From the stoichiometry:

• Reduction of $1\text{ mol}$ of $\text{MnO}_4^-$ to produce $1\text{ mol}$ of $\text{Mn}^{2+}$ requires $5\text{ moles}$ of electrons $= 5\text{ F}$ of charge.
• To obtain $2\text{ moles}$ of $\text{Mn}^{2+}$, the required charge is:
  $$Q = 2 \times 5\text{ F} = 10\text{ F}$$

Reaction analysis:

• Hydration of unsymmetrical or non-ethyne alkynes in presence of $\text{H}_2\text{SO}_4/\text{HgSO}_4$ forms ketones (e.g., propyne gives acetone).
• Ozonolysis of tetra-substituted or tri-substituted alkenes produces ketones.
• Treatment of alkyl nitriles ($\text{R-CN}$) with Grignard reagents followed by acid hydrolysis yields ketones ($\text{R-CO-R'}$).
• Stephen's reaction involves the reduction of nitriles with stannous chloride ($\text{SnCl}_2$) in the presence of $\text{HCl}$ followed by hydrolysis to specifically yield aldehydes (not ketones):
  $$\text{R-CN} + \text{SnCl}_2 + \text{HCl} \rightarrow \text{R-CH=NH}\cdot\text{HCl} \xrightarrow{\text{H}_3\text{O}^+} \text{R-CHO}$$