19.4 Amines and Amides

Learning Objectives

By the end of this section, you will be able to:
  • Classify amines and amides

Amines

Amines are molecules that contain carbon-nitrogen bonds. The nitrogen atom in an amine has a lone pair of electrons and three bonds to other atoms, either carbon or hydrogen. Various nomenclatures are used to derive names for amines, but all involve the class-identifying suffix –ine as illustrated here for a few simple examples in Figure 19.4a.

Three structures are shown, each with a red, central N atom which has a pair of electron dots indicated in red above the N atoms. The first structure is labeled methyl amine. To the left of the N, a C H subscript 3 group is bonded. H atoms are bonded to the right and bottom of the central N atom. The second structure is labeled dimethyl amine. This structure has C H subscript 3 groups bonded to the left and right of the N atom and a single H atom is bonded below. The third structure is labeled trimethyl amine, which has C H subscript 3 groups bonded to the left, right, and below the central N atom.
Figure 19.4a. The simplest amines: methyl amine, dimethyl amine and trimethyl amine (credit: Chemistry (OpenStax), CC BY 4.0).

In some amines, the nitrogen atom replaces a carbon atom in an aromatic hydrocarbon. Pyridine (Figure 19.4b) is one such heterocyclic amine. A heterocyclic compound contains atoms of two or more different elements in its ring structure.

A molecular structure is shown. A ring of five C atoms and one N atom is shown with alternating double bonds. Single H atoms are bonded, appearing at the outside of the ring on each C atom. The N atom has an unshared electron pair shown on the N atom on the outer side of the ring. The N atom, electron dot pair, and bonds connected to it in the ring are shown in red.
Figure 19.4b. The illustration shows one of the resonance structures of pyridine (credit: Chemistry (OpenStax), CC BY 4.0).

Like ammonia, amines are weak bases (Figure 19.4c), due to the lone pair of electrons on their nitrogen atoms:

Two reactions are shown. In the first, ammonia reacts with H superscript plus. An unshared pair of electron dots sits above the N atom. To the left, right, and bottom, H atoms are bonded. This is followed by a plus symbol and an H atom with a superscript plus symbol. To the right of the reaction arrow, ammonium ion is shown in brackets with a superscript plus symbol outside. Inside the brackets, the N atom is shown with H atoms bonded on all four sides. In a very similar second reaction, methyl amine reacts with H superscript plus to yield methyl ammonium ion. The methyl amine structure is like ammonia except a C H subscript 3 group is attached in place of the left most H atom in the structure. Similarly, the resulting methyl ammonium ion is represented in brackets with a superscript plus symbol appearing outside. Inside, the structure is similar to that of methyl amine except that an H atom appears at the top of the N atom where the unshared electron pair was previously shown.
Figure 19.4c. Methyl amine, an example, to demonstrate how amines are weak bases similar to ammonia (credit: Chemistry (OpenStax), CC BY 4.0).

The basicity of an amine’s nitrogen atom plays an important role in much of the compound’s chemistry. Amine functional groups are found in a wide variety of compounds, including natural and synthetic dyes, polymers, vitamins, and medications such as penicillin and codeine. They are also found in many molecules essential to life, such as amino acids, hormones, neurotransmitters, and DNA.

Spotlight on Everyday Chemistry: Addictive Alkaloids

Since ancient times, plants have been used for medicinal purposes. One class of substances, called alkaloids, found in many of these plants has been isolated and found to contain cyclic molecules with an amine functional group. These amines are bases. They can react with H3O+ in a dilute acid to form an ammonium salt, and this property is used to extract them from the plant:

[latex]\text{R}_3\text{N}\;+\;\text{H}_3\text{O}^{+}\;+\;\text{Cl}^{-}\;{\longrightarrow}\;[\text{R}_3\text{NH}^{+}]\;\text{Cl}^{-}\;+\;\text{H}_2\text{O}[/latex]

The name alkaloid means “like an alkali.” Thus, an alkaloid reacts with acid. The free compound can be recovered after extraction by reaction with a base:

[latex][\text{R}_3\text{NH}^{+}]\;\text{Cl}^{-}\;+\;\text{OH}^{-}\;{\longrightarrow}\;\text{R}_3\text{N}\;+\;\text{H}_2\text{O}\;+\;\text{Cl}^{-}[/latex]

The structures of many naturally occurring alkaloids have profound physiological and psychotropic effects in humans. Examples of these drugs include nicotine, morphine, codeine, and heroin (Figure 19.4d). The plant produces these substances, collectively called secondary plant compounds, as chemical defenses against the numerous pests that attempt to feed on the plant:

Molecular structures of nicotine, morphine, codeine, and heroin are shown. These large structures share some common features, including rings. In the complex structures of morphine, codeine, and heroin, bonds to some O atoms in the structures are indicated with dashed wedges and bonds to some H atoms and N atoms are shown as solid wedges.
Figure 19.4d. The structural images of drugs include nicotine, morphine, codeine, and heroin (credit: Chemistry (OpenStax), CC BY 4.0).

In these diagrams, as is common in representing structures of large organic compounds, carbon atoms in the rings and the hydrogen atoms bonded to them have been omitted for clarity. The solid wedges indicate bonds that extend out of the page. The dashed wedges indicate bonds that extend into the page. Notice that small changes to a part of the molecule change the properties of morphine, codeine, and heroin. Morphine, a strong narcotic used to relieve pain, contains two hydroxyl functional groups, located at the bottom of the molecule in this structural formula. Changing one of these hydroxyl groups to a methyl ether group forms codeine, a less potent drug used as a local anesthetic. If both hydroxyl groups are converted to esters of acetic acid, the powerfully addictive drug heroin results (Figure 19.4e).

This is a photo of a field of red-orange poppies.
Figure 19.4e. Poppies can be used in the production of opium, a plant latex that contains morphine from which other opiates, such as heroin, can be synthesized (credit: Karen Roe, Chemistry (Open Stax), CC BY 4.0).

Read more about the colours of poppies in Compound Interest: The chemistry of poppies: colours and opium (compoundchem.com).

Furthermore, in some foods that contain poppy seeds, trace amounts of codeine and morphine are present up to 48 hours in urine. In Hungary, there is a sweet roll filled with poppy seeds along with a walnut or chestnut paste, known as Bejgli often served at Christmas. For more information on the Bejgli dessert, see Compound Chemistry Advent 2023.

Amides

Amides are molecules that contain nitrogen atoms connected to the carbon atom of a carbonyl group (Figure 19.4f). Like amines, various nomenclature rules may be used to name amides, but all include use of the class-specific suffix -amide:

This figure shows three structures. Two examples are provided. The basic structure has an H atom or R group bonded to a C atom which is double bonded to an O atom. The O atom as two sets of electron dots. The C atom is bonded to an N atom which in turn is bonded to two R groups or two H atoms. The N atom as one set of electron dots. The next structure includes acetamide, which has C H subscript 3 bonded to a C atom with a doubly bonded O atom. The second C atom is also bonded to N H subscript 2. Hexanamide has a hydrocarbon chain of length 6 involving all single bonds. The condensed structure is shown here. To the sixth C atom at the right end of the chain, an O atom is double bonded and an N H subscript 2 group is single bonded.
Figure 19.4f. Examples of amides acetamide (bottom left) and hexanamide (bottom right) with the top structure representing the amide functional group (credit: Chemistry (Open Stax), CC BY 4.0).

Amides can be produced when carboxylic acids react with amines or ammonia in a process called amidation (Figure 19.4g). A water molecule is eliminated from the reaction, and the amide is formed from the remaining pieces of the carboxylic acid and the amine.

 

A chemical reaction is shown between a carboxylic acid and amine to form an amide and water. Structures are shown. The carboxylic acid is shown as a C H subscript 3 group bonded to a C H subscript 2 group bonded to a C atom with a double bonded O atom above and an O H group bonded to the right. There is a plus sign. The amine is shown as an N atom with two H atoms bonded to the bottom and left sides. A C H subscript 3 group is bonded to the right side of the N atom. To the right of an arrow, an amide is shown as a C H subscript 3 group bonded to a C H subscript 2 group bonded to a C atom which is double bonded to an O atom above and an N with an H atom bonded below. The N atom is bonded to a C H subscript 3 group. The final product indicated after a plus sign is water, H subscript 2 O.
Figure 19.4g. The reaction between a carboxylic acid and an amine produces an amide and water (credit: Chemistry (Open Stax), CC BY 4.0).

Attribution & References

Except where otherwise noted, this page is adapted by Adrienne Richards from “18.4 Amines and Amides” In General Chemistry 1 & 2 by Rice University, a derivative of Chemistry (Open Stax) by Paul Flowers, Klaus Theopold, Richard Langley & William R. Robinson and is licensed under CC BY 4.0. ​Access for free at Chemistry (OpenStax)

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Organic and Biochemistry Supplement to Enhanced Introductory College Chemistry Copyright © 2024 by Gregory Anderson; Caryn Fahey; Adrienne Richards; Samantha Sullivan Sauer; David Wegman; and Jen Booth is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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