Will be mentioned at relevant places — Core Principles

Core Principles

Cyanides, or nitriles, contain the $-\text{C}\equiv\text{N}$ functional group, where carbon is triply bonded to nitrogen. They are structural isomers of isocyanides, or carbylamines, which contain the $-\text{N}\equiv\text{C}$ group, with nitrogen directly bonded to the organic group.

The cyanide ion ($\text{CN}^-$) is an ambidentate nucleophile, meaning it can attack through either carbon or nitrogen. This leads to a key distinction: alkyl halides react with ionic $\text{KCN}$ to form nitriles ($\text{R}-\text{C}\equiv\text{N}$), but with covalent $\text{AgCN}$ to form isocyanides ($\text{R}-\text{N}\equiv\text{C}$).

Nitriles can be prepared from alkyl halides, aldehydes/ketones (cyanohydrins), or amides (dehydration). Their reactions include hydrolysis to carboxylic acids, reduction to primary amines, and reaction with Grignard reagents to form ketones.

Isocyanides are famously prepared via the Carbylamine reaction, a test for primary amines, and also from alkyl halides with $\text{AgCN}$. Isocyanides hydrolyze to primary amines and formic acid, and reduce to secondary amines.

Both classes are important synthetic intermediates, though their high toxicity necessitates careful handling.

Often confused with

Side-by-side differences the NEET paper likes to test.

Will be mentioned at relevant places vs Isocyanides

Aspect	Will be mentioned at relevant places	Isocyanides
Functional Group	$-\text{C}\equiv\text{N}$ (Cyano group)	$-\text{N}\equiv\text{C}$ (Isocyano group)
Nomenclature	Nitriles (e.g., Ethanenitrile)	Isocyanides or Carbylamines (e.g., Ethane isocyanide)
Bonding to R-group	Carbon of the cyano group is bonded to the R-group.	Nitrogen of the isocyano group is bonded to the R-group.
Preparation from R-X	React with $\text{KCN}$ (ionic) to form nitriles.	React with $\text{AgCN}$ (covalent) to form isocyanides.
Hydrolysis Products	Yield carboxylic acids ($\text{RCOOH}$) and ammonia.	Yield primary amines ($\text{RNH}_2$) and formic acid ($\text{HCOOH}$).
Reduction Products	Yield primary amines ($\text{RCH}_2\text{NH}_2$).	Yield secondary amines ($\text{RNHCH}_3$).
Odor	Generally pleasant or almond-like (e.g., benzonitrile).	Extremely foul and offensive smell.
Carbylamine Test	Do not give this test.	Are the products of this test, used to identify primary amines.

Cyanides and isocyanides are structural isomers with distinct chemical properties. Cyanides feature a carbon-nitrogen triple bond where the carbon is linked to the organic group, while isocyanides have the nitrogen linked to the organic group.

This structural difference leads to varied reactivity, particularly in their formation from alkyl halides (KCN vs. AgCN), their hydrolysis products (carboxylic acids vs. primary amines and formic acid), and their reduction products (primary amines vs.

secondary amines). Isocyanides are famously characterized by their foul odor and are the products of the Carbylamine reaction, a key test for primary amines, which cyanides do not undergo.

Why it is tested: For NEET, understanding the differences between cyanides and isocyanides is crucial for predicting reaction products, identifying reagents, and applying distinguishing tests. Questions frequently test the ambidentate nature of the cyanide ion, the Carbylamine reaction, and the hydrolysis/reduction products of both functional groups. Mastery of these distinctions is essential for scoring well in organic chemistry sections.