Ch 9Amines — Class 12 Chemistry, concept-first.

Amines form one of the most significant classes of organic nitrogen compounds — each one is built by replacing one or more hydrogen atoms of ammonia () with an alkyl or aryl group.

Amines are a major class of organic compounds obtained when one, two, or all three of the hydrogen atoms of an ammonia molecule () are replaced by alkyl and/or aryl groups.

Every amine can be pictured as ammonia, , with one or more of its hydrogen atoms swapped out for an alkyl or aryl group.

Amines can be named either by the older common-name system or by the systematic IUPAC system, and the two use quite different logic.

Amines are rarely built by attaching nitrogen directly; instead they are almost always obtained by transforming a nitrogen-containing functional group that is already present in some other compound.

The most direct route to a primary amine is to start from the corresponding nitro compound and simply reduce the group down to .

An alkyl or benzyl halide contains a carbon–halogen bond that is readily cleaved by a nucleophile — this is the same substitution chemistry used elsewhere for haloalkanes.

Nitriles () can be reduced to give primary amines. Two reducing systems accomplish this: lithium aluminium hydride (), or catalytic hydrogenation (hydrogen gas over a metal catalyst such as nickel, or…

Amides can also be reduced to amines. Treatment of an amide with lithium aluminium hydride, followed by aqueous work-up, converts the carbonyl carbon of the amide into a group and yields the correspon…

Gabriel synthesis is a method built specifically to give primary amines, and it is prized because — unlike ammonolysis of alkyl halides (Section 9.4.2) — it delivers the primary amine cleanly, without…

Hoffmann devised a method for making primary amines starting not from a halide or nitrile but from an amide. The amide is treated with bromine in an aqueous or ethanolic solution of sodium hydroxide.

The lightest aliphatic amines occur as gases and carry a characteristic fishy, ammonia-like smell. As the carbon skeleton grows, primary amines bearing three or more carbon atoms turn into liquids, an…

The nitrogen atom of an amine carries a lone pair of electrons, and it is this lone pair that governs almost everything amines do chemically.

Because nitrogen holds an unshared electron pair, amines readily accept a proton from an acid and are therefore classified as Lewis bases.

Because amines are good nucleophiles, they can attack an alkyl halide directly in a nucleophilic substitution reaction, displacing the halide and installing a new alkyl group on nitrogen:

Primary and secondary amines — both aliphatic and aromatic — carry at least one N–H bond, and this hydrogen can be replaced by an acyl group () when the amine reacts with an acid chloride, an acid anh…

When a primary amine is warmed with chloroform and ethanolic (alcoholic) potassium hydroxide, it is converted into an isocyanide (also called a carbylamine).

Nitrous acid () is too unstable to be stored, so it is always generated in situ, right inside the reaction mixture, by treating sodium nitrite with a mineral acid such as hydrochloric acid:

Benzenesulphonyl chloride, , is commonly known as Hinsberg's reagent. It reacts with primary and secondary amines to form sulphonamides, and the way each class of amine behaves toward it — together wi…

Aromatic amines such as aniline undergo electrophilic substitution readily, and the reason traces directly back to the resonance picture of aniline discussed earlier in this chapter.

Diazonium salts have the general formula , where R is an aryl group and may be , , , , etc. The group is called the diazonium group.

Benzenediazonium chloride, the parent member of this class, occurs as a colourless solid with a well-defined crystalline form.

The diazonium group, , sits on the aromatic ring only briefly — its whole synthetic value lies in what happens to it next.

The diazonium group is a very good leaving group, and when the ring reacts with a suitable nucleophile, nitrogen is expelled from the molecule as gas while the nucleophile takes its place on the aroma…

Instead of being displaced, the diazonium group can also stay fully intact in the product. Here the diazonium ion behaves as a weak electrophile, and it attacks a second, electron-rich aromatic ring i…

Taken together, the substitution and coupling reactions of diazonium salts show that the group can be swapped out for a wide range of other groups.

- Amines are derivatives of ammonia () where one or more hydrogen atoms are replaced by alkyl/aryl groups ( or ).

These are the final answers printed at the end of the NCERT chapter. The book gives answers for some intext questions only — every question below links to our complete worked solution.

Higher-order thinking / exemplar-style practice problems.

Sample papers and previous-year board questions for this subject.