Alkyl halide is converted into alkyl isocyanide by reaction with

Step 1: Understand ambidentate nucleophiles

Cyanide ion ($\ce{CN-}$) is an ambidentate nucleophile - it can attack through:

• Carbon (C-attack) → nitrile ($\ce{R-C≡N}$)
• Nitrogen (N-attack) → isocyanide ($\ce{R-N≡C}$)

Step 2: Ionic vs Covalent cyanide salts

Ionic salts (NaCN, KCN, NH₄CN):

• Free $\ce{CN-}$ ion in solution
• Attack through carbon (more electronegative, better nucleophile)
• Product: Nitrile ($\ce{R-CN}$)

$\ce{R-X + NaCN -> R-CN + NaX}$

Covalent salts (AgCN):

• Covalent Ag-CN bond
• Metal bonded to carbon end
• Nucleophile attacks through nitrogen end
• Product: Isocyanide ($\ce{R-NC}$)

$\ce{R-X + AgCN -> R-NC + AgX}$

Step 3: Identify the correct reagent

For alkyl isocyanide formation: Use AgCN (covalent)

For alkyl nitrile formation: Use NaCN/KCN (ionic)

Answer: (d) AgCN

Key Distinctions:

| Reagent | Type | Product | Structure | |---------|------|---------|------------| | NaCN, KCN | Ionic | Nitrile | $\ce{R-C≡N}$ | | AgCN | Covalent | Isocyanide | $\ce{R-N≡C}$ |

Memory Aid:

• Ionic → C-attack → Nitrile (CN)
• Covalent (Ag) → N-attack → Isocyanide (NC)

Similar behavior with nitrite:

• NaNO₂ (ionic) → alkyl nitrite ($\ce{R-O-N=O}$)
• AgNO₂ (covalent) → nitroalkane ($\ce{R-NO2}$)