Will be mentioned at relevant places — Revision Notes

⚡ 30-Second Revision

Cyanides (Nitriles): — $-\text{C}\equiv\text{N}$ group. Carbon attached to R-group.
Isocyanides (Carbylamines): — $-\text{N}\equiv\text{C}$ group. Nitrogen attached to R-group.
Ambidentate $\text{CN}^-$: — Attacks via C (with $\text{KCN}$) $\rightarrow$ Nitriles ($\text{R}-\text{C}\equiv\text{N}$). Attacks via N (with $\text{AgCN}$) $\rightarrow$ Isocyanides ($\text{R}-\text{N}\equiv\text{C}$).
Nitrile Hydrolysis: — $\text{R}-\text{C}\equiv\text{N} \xrightarrow{\text{H}^+/\text{OH}^-} \text{RCOOH}$ (Carboxylic acid).
Nitrile Reduction: — $\text{R}-\text{C}\equiv\text{N} \xrightarrow{\text{LiAlH}_4/\text{H}_2\,\text{Ni}} \text{RCH}_2\text{NH}_2$ (Primary amine).
Isocyanide Hydrolysis: — $\text{R}-\text{N}\equiv\text{C} \xrightarrow{\text{H}^+} \text{RNH}_2 + \text{HCOOH}$ (Primary amine + Formic acid).
Isocyanide Reduction: — $\text{R}-\text{N}\equiv\text{C} \xrightarrow{\text{H}_2\,\text{Ni}} \text{RNHCH}_3$ (Secondary amine).
Carbylamine Reaction: — Primary amine + $\text{CHCl}_3$ + alc. $\text{KOH} \xrightarrow{Delta} \text{RNC}$ (foul smell). Test for primary amines.

2-Minute Revision

Cyanides (nitriles) and isocyanides (carbylamines) are structural isomers, differing in how the $\text{C}\equiv\text{N}$ unit connects to the organic chain. Nitriles have the carbon directly attached ($\text{R}-\text{C}\equiv\text{N}$), while isocyanides have the nitrogen directly attached ($\text{R}-\text{N}\equiv\text{C}$).

A key concept is the ambidentate nature of the cyanide ion: with ionic $\text{KCN}$, alkyl halides yield nitriles, but with covalent $\text{AgCN}$, they yield isocyanides. Nitriles are versatile; they hydrolyze to carboxylic acids and reduce to primary amines.

Isocyanides are known for their extremely foul odor and are formed in the Carbylamine reaction, a specific test for primary amines. Isocyanides hydrolyze to primary amines and formic acid, and reduce to secondary amines.

Remember these distinct reaction pathways and products, especially for hydrolysis and reduction, as they are frequently tested in NEET.

5-Minute Revision

To ace questions on cyanides and isocyanides, focus on their fundamental differences and key reactions. Structurally, nitriles are $\text{R}-\text{C}\equiv\text{N}$ and isocyanides are $\text{R}-\text{N}\equiv\text{C}$, making them linkage isomers. The ambidentate nature of the cyanide ion is critical: $\text{KCN}$ (ionic) reacts with alkyl halides via carbon to form nitriles, while $\text{AgCN}$ (covalent) reacts via nitrogen to form isocyanides. This distinction is a common trap.

Preparation:

Nitriles: — From alkyl halides ($\text{R}-\text{X} + \text{KCN}$), from amides (dehydration), or from aldehydes/ketones (cyanohydrin formation).
Isocyanides: — From alkyl halides ($\text{R}-\text{X} + \text{AgCN}$) or via the Carbylamine reaction.

Reactions:

Nitriles:

* Hydrolysis: Complete hydrolysis yields carboxylic acids ($\text{RCOOH}$). Partial hydrolysis yields amides ($\text{RCONH}_2$). * Reduction: With $\text{LiAlH}_4$ or catalytic hydrogenation, they yield primary amines ($\text{RCH}_2\text{NH}_2$). With DIBAL-H, they can yield aldehydes. * Grignard: React with $\text{R}'\text{MgX}$ to form ketones ($\text{RCOR}'$) after hydrolysis.

Isocyanides:

* Hydrolysis: Yields primary amines ($\text{RNH}_2$) and formic acid ($\text{HCOOH}$). * Reduction: Yields secondary amines ($\text{RNHCH}_3$).

Carbylamine Reaction: This is a diagnostic test for primary amines. A primary amine, $\text{CHCl}_3$, and alcoholic $\text{KOH}$ are heated to produce a foul-smelling isocyanide. Secondary and tertiary amines do not react. This reaction is a high-yield topic for NEET. Always remember the characteristic foul smell of isocyanides. Practice predicting products for various starting materials and reagents to solidify your understanding.

Prelims Revision Notes

Cyanides (Nitriles) & Isocyanides (Carbylamines) - NEET Revision

1. Structures & Isomerism:

Nitriles: — $\text{R}-\text{C}\equiv\text{N}$ (Cyano group). Carbon of $\text{C}\equiv\text{N}$ attached to R-group.
Isocyanides: — $\text{R}-\text{N}\equiv\text{C}$ (Isocyano group). Nitrogen of $\text{N}\equiv\text{C}$ attached to R-group.
They are linkage isomers (a type of structural isomerism).

2. Ambidentate Nature of $\text{CN}^-$:

$\text{KCN}$ (ionic): — Provides free $\text{CN}^-$. Carbon is the 'soft' nucleophile, attacks alkyl halides ($\text{R}-\text{X}$) to form Nitriles ($\text{R}-\text{C}\equiv\text{N}$). Reaction: $\text{R}-\text{X} + \text{KCN} \xrightarrow{\text{Alcohol}} \text{R}-\text{C}\equiv\text{N} + \text{KX}$.
$\text{AgCN}$ (covalent): — Nitrogen is the 'hard' nucleophile, attacks alkyl halides ($\text{R}-\text{X}$) to form Isocyanides ($\text{R}-\text{N}\equiv\text{C}$). Reaction: $\text{R}-\text{X} + \text{AgCN} \xrightarrow{\text{Alcohol}} \text{R}-\text{N}\equiv\text{C} + \text{AgX}$.

3. Preparation Methods:

Nitriles:

* From Alkyl Halides: $\text{R}-\text{X} + \text{KCN} \rightarrow \text{R}-\text{C}\equiv\text{N}$ * From Amides (Dehydration): $\text{RCONH}_2 \xrightarrow{\text{P}_2\text{O}_5/Delta} \text{R}-\text{C}\equiv\text{N}$ * From Aldehydes/Ketones (Cyanohydrins): $\text{RCHO} + \text{HCN} \xrightarrow{\text{Base}} \text{RCH(OH)CN}$ * Sandmeyer Reaction: $\text{ArN}_2^+\text{Cl}^- \xrightarrow{\text{CuCN}} \text{Ar}-\text{C}\equiv\text{N}$

Isocyanides:

* From Alkyl Halides: $\text{R}-\text{X} + \text{AgCN} \rightarrow \text{R}-\text{N}\equiv\text{C}$ * Carbylamine Reaction (Isocyanide Test): $\text{RNH}_2 + \text{CHCl}_3 + 3\text{KOH} \xrightarrow{Delta} \text{R}-\text{N}\equiv\text{C}$ (foul smell)

4. Key Reactions & Products:

**Nitriles ($\text{R}-\text{C}\equiv\text{N}$):**

* Hydrolysis: * Complete: $\text{R}-\text{C}\equiv\text{N} + 2\text{H}_2\text{O} \xrightarrow{\text{H}^+/\text{OH}^-} \text{RCOOH}$ (Carboxylic acid) * Partial: $\text{R}-\text{C}\equiv\text{N} + \text{H}_2\text{O} \xrightarrow{\text{mild}} \text{RCONH}_2$ (Amide) * Reduction: * $\text{R}-\text{C}\equiv\text{N} \xrightarrow{\text{1.

LiAlH}_4\, \text{2. H}_2\text{O}} \text{RCH}_2\text{NH}_2$(Primary amine) *$\text{R}-\text{C}\equiv\text{N} \xrightarrow{\text{1. DIBAL-H, -78}^\circ\text{C}, \text{2. H}_2\text{O}} \text{RCHO}$(Aldehyde) * **Grignard Reaction:**$\text{R}-\text{C}\equiv\text{N} + \text{R}'\text{MgX} \xrightarrow{\text{1.

Ether, 2.

**Isocyanides ($\text{R}-\text{N}\equiv\text{C}$):**

* Hydrolysis: $\text{R}-\text{N}\equiv\text{C} + 2\text{H}_2\text{O} \xrightarrow{\text{H}^+} \text{RNH}_2 + \text{HCOOH}$ (Primary amine + Formic acid) * Reduction: $\text{R}-\text{N}\equiv\text{C} \xrightarrow{\text{H}_2/\text{Ni}} \text{RNHCH}_3$ (Secondary amine)

5. Carbylamine Reaction (Isocyanide Test):

Reagents: — Primary amine ($\text{RNH}_2$), $\text{CHCl}_3$, alcoholic $\text{KOH}$.
Product: — Foul-smelling Isocyanide ($\text{RNC}$).
Specificity: — Only primary amines (aliphatic & aromatic) give this test. Secondary and tertiary amines do not. Crucial for distinguishing amines.

Vyyuha Quick Recall

To remember the $\text{KCN}$ vs $\text{AgCN}$ products:

King Cyanide makes Nitriles (KCN $\rightarrow$ Nitriles) Agent Gold makes Isocyanides (AgCN $\rightarrow$ Isocyanides)

And for the Carbylamine test: Chloroform, Hydroxide, Amine, Really Bad Yucky Liquid (Carbylamine reaction for primary amines, producing foul-smelling isocyanides).