Chapter 26 – Summary

26.1 Amines – Structure and Naming

Amines are nitrogen-containing organic molecules derived from ammonia (NH₃). A primary (1°) amine (RNH₂) has one organic group bonded to the nitrogen atom, a secondary (2°) amine (R₂NH) has two organic groups bonded to the nitrogen atom, and a tertiary (3°) amine (R₃N) has three organic groups bonded to the nitrogen atom. A cyclic compound in which the ring contains one or more noncarbon atoms is called a heterocyclic compound. Alkaloids are heterocyclic amines found in many plants. Caffeine, nicotine, and cocaine are familiar alkaloids.

An amine is a derivative of ammonia in which one, two, or all three hydrogen atoms are replaced by hydrocarbon groups.

Amines are classified as primary, secondary, or tertiary by the number of hydrocarbon groups attached to the nitrogen atom. Amines are named by naming the alkyl groups attached to the nitrogen atom, followed by the suffix –amine.

26.2 Amines – Physical Properties

Primary and secondary amines have higher boiling points than those of alkanes or ethers of similar molar mass because they can engage in intermolecular hydrogen bonding. Their boiling points are lower than those of alcohols because alcohol molecules have hydrogen atoms bonded to an oxygen atom, which is more electronegative.

The boiling points of tertiary amines, which cannot engage in hydrogen bonding because they have no hydrogen atom on the nitrogen atom, are comparable to those of alkanes and ethers of similar molar mass.

Because all three classes of amines can engage in hydrogen bonding with water, amines of low molar mass are quite soluble in water.

26.3 Heterocyclic Nitrogen Compounds

Amines are bases; they react with acids to form salts. Salts of aniline are properly named as anilinium compounds, but an older system is used to name drugs: the salts of amine drugs and hydrochloric acid are called “hydrochlorides.” Heterocyclic amines are cyclic compounds with one or more nitrogen atoms in the ring.

26.4 Basicity of Amines

Amines are weak bases due to the lone pair of electrons on their nitrogen atoms. They can accept protons. Nearly all amines, including those that are not very soluble in water, will react with strong acids to form salts soluble in water.

26.5 Amides – Structures, Properties and Naming

Organic compounds containing a carbonyl group bonded to a nitrogen atom are amides, and the carbon-to-nitrogen bond is an amide linkage (or a peptide linkage). Most amides are colourless and odourless, and the lighter ones are soluble in water. Because they are polar molecules, amides have comparatively high boiling points and melting points. Amides are synthesized from carboxylic acids and NH₃ or amines. Amides are neutral compounds. They resist hydrolysis in water, but acids, bases, and enzymes catalyze the reaction.

Most amides are solids at room temperature; the boiling points of amides are much higher than those of alcohols of similar molar mass. Amides of five or fewer carbon atoms are soluble in water. Amides are prepared by the reaction of a carboxylic acid with ammonia or an amine.

26.6 Chemical Properties of Amines and Amides

The hydrolysis of an amide produces a carboxylic acid and ammonia. Primary amides are formed from the reaction of a carboxylic acid with ammonia.  Secondary amides are formed from the reaction of a carboxylic acid and a primary amine. Tertiary amides are formed from the reaction of a carboxylic acid and a secondary amine. Amines are formed through the reduction of amides or the reduction of nitriles. Amines can also be formed through the alkyl halide substitution of ammonia or lower classed amines.

Attribution & References

Except where otherwise noted, this content has been adapted by Caryn Fahey and Samantha Sullivan Sauer from:

• 26.1 Summary -“15.18 End-of-Chapter Material” In Introduction to Chemistry: General, Organic, and Biological (v. 1.0), CC BY-NC-SA 3.0 and “15.11 Amines: Structures and Names” In Introduction to Chemistry: General, Organic, and Biological (v. 1.0), CC BY-NC-SA 3.0
• 26.2 Summary – “15.12 Physical Properties of Amines” In Introduction to Chemistry: General, Organic, and Biological (v. 1.0), CC BY-NC-SA 3.0
• 26.3 summary – “15.13 Amines as Bases” In Introduction to Chemistry: General, Organic, and Biological (v. 1.0), CC BY-NC-SA 3.0
• 26.4 summary – “11.10: Chemical Properties: Amines as Bases” In USC Upstate: CHEM U109 – Chemistry of Living Things (Mueller),  CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.
• 26.5 summary – “18.15 Physical properties of amides“, “18.14 Amides: Structures and Names“, “18.16 Formation of Amides” and End-of-Chapter Material In Introduction to Chemistry: GOB (v. 1.0), CC BY-NC 3.0
• 26.6 summary – “18.17 Chemical Properties of Amides: Hydrolysis” and written by Samantha Sullivan Sauer