26.5 Amides – Structures, Properties and Naming

Learning Objectives

By the end of this section, you will be able to:

  • Identify the general structure for an amide.
  • Identify the functional group for an amide.
  • Names amides with common names.
  • Name amides according to the IUPAC system.
  • Compare the boiling points of amides with alcohols of similar molar mass.
  • Compare the solubilities in water of amides of five or fewer carbon atoms with the solubilities of comparable alkanes and alcohols in water.

Amides are molecules that contain nitrogen atoms connected to the carbon atom of a carbonyl group. If the two remaining bonds on the nitrogen atom are attached to hydrogen atoms, the compound is a simple amide. If one or both of the two remaining bonds on the atom are attached to alkyl or aryl groups, the compound is a substituted amide (Figure 26.5a.).

The diagram shows the structural formulas representing an amide group. It then distinguishes between a simple amide which has hydrogens attached to the remaining bond space of nitrogen vs substituted amides which have alkyl or aryl groups as well as a hydrogen attached to the bond space of the nitrogen.
Figure 26.5a. Amide groups (Credit: Introduction to Chemistry: GOB (V. 1.0)., CC BY-NC-SA 3.0).

The carbonyl carbon-to-nitrogen bond is called an amide linkage. This bond is quite stable and is found in the repeating units of protein molecules, where it is called a peptide linkage.

Naming Amides

  1. Primary amides are named by changing the name of the acid by dropping the -oic acid or -ic acid endings and adding -amide.
  2. The carbonyl carbon is numbered carbon 1 on it’s location. It is not necessary to include the location number in the name because it is assumed that the functional group will be on the end of the parent chain.
  3. Secondary amides are named by using an upper case N to designate that the alkyl group is on the nitrogen atom. Alkyl groups attached to the nitrogen are named as substituents. The letter N is used to indicate they are attached to the nitrogen.
  4. Tertiary amides are named in the same way as secondary amides, but with two N’s

Simple amides are named as derivatives of carboxylic acids. The –ic ending of the common name or the –oic ending of the International Union of Pure and Applied Chemistry (IUPAC) name of the carboxylic acid is replaced with the suffix –amide (Figure 26.5b.).

The image depicts the structural formula for formic acid, which displays a carbon double bonded to an oxygen and bonded to a hydroxide group. It also shows a formamide group, which displays carbon double bonded to oxygen and bonded to nitrogen.
Figure 26.5b. Comparison of Formic acid and Formamide (Credit: Introduction to Chemistry: GOB (V. 1.0)., CC BY-NC-SA 3.0).
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 26.5c. Basic structure of an amide showcasing functional groups (credit: General Chemistry 1 & 2 , CC BY 4.0).

Amides can be produced when carboxylic acids react with amines or ammonia in a process called amidation. A water molecule is eliminated from the reaction, and the amide is formed from the remaining pieces of the carboxylic acid and the amine (Figure 26.5d.) (note the similarity to formation of an ester from a carboxylic acid and an alcohol discussed in the previous section).

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 26.5d. Chemical reaction for formation of an amide (credit: General Chemistry 1 & 2 , CC BY 4.0).

Example 26.5a

Give the IUPAC name for the following amides.

  1. CH3CH2C=O(NH2)
  2. CH3C=O(NH)CH2CH3

Solution

  1. propanamide (proprionamide)
  2. N-ethylethanamide (N-ethylacetamide)

Exercise 26.5a

Write the IUPAC name for each of the following amides.

  1. CH3CH2CH2CH2C=O(NH2)
  2. CH3CH2CHClCH2C=O(NH2)
A central nitrogen with an ethyl group attached, as well as a hydrogen and a single carbon with a double bonded oxygen and a benzene ring.
(credit: 2D structure image of CID 11959 (N-Ethylbenzamide) via PubChem)

Check your answers: [1]

Exercise 26.5b

Name each compound with the common name, the IUPAC name or both.

An Nh2 attached to a 2 carbon chain with a double bonded oxygen on the middle carbon.
(Credit: Introduction to Chemistry: GOB (V. 1.0)., CC BY-NC-SA 3.0).

b.

A central nitrogen with a methyl group and a 4 carbon chain attached. The first carbon after the nitrogen group in the 4 carbon chain also has a double bonded oxygen.
(credit: credit: 2D structure image of 28774 (N-Methylbutyramide) via PubChem).

Check your answers: [2]

The reaction between amines and carboxylic acids to form amides is biologically important. It is through this reaction that amino acids (molecules containing both amine and carboxylic acid substituents) link together in a polymer to form proteins.

Proteins and Enzymes

Proteins are large biological molecules made up of long chains of smaller molecules called amino acids. Organisms rely on proteins for a variety of functions—proteins transport molecules across cell membranes, replicate DNA, and catalyze metabolic reactions, to name only a few of their functions. The properties of proteins are functions of the combination of amino acids that compose them and can vary greatly. Interactions between amino acid sequences in the chains of proteins result in the folding of the chain into specific, three-dimensional structures that determine the protein’s activity.

Enzymes are large biological molecules, mostly composed of proteins, which are responsible for the thousands of metabolic processes that occur in living organisms. Enzymes are highly specific catalysts; they speed up the rates of certain reactions. Enzymes function by lowering the activation energy of the reaction they are catalyzing, which can dramatically increase the rate of the reaction. Most reactions catalyzed by enzymes have rates that are millions of times faster than the non-catalyzed version.

For more information on proteins see Chapter 28.3 Amino Acids, Proteins and Enzymes.

Spotlight on Everyday Chemistry: Acrylamide

Acrylamide is found mainly in foods made from plants, that are high in carbohydrates and low in proteins. Examples of such foods include potato products, grain products or coffee. Acrylamide is more likely to build up when foods are cooked for longer periods of time or at higher temperatures. Acrylamide is known to cause cancer in experimental animals and is therefore a possible human carcinogen.

Infographic 26.5a.  Infographic describing acrylamide and it’s possible increase in cancer risk. Read more about “Chemical Concerns – Does Acrylamide in Toast & Roast Potatoes Cause Cancer?” by Andy Brunning / Compound Interest, CC BY-NC-ND, or access a text-based summary of infographic 26.5a [New tab].

Watch Properties of Amides on YouTube (8 min).

Video Source: Professor Dave Explains. (2019, September 19). Properties of Amides. [Video]. YouTube.

Indigenous Perspectives: Hakarl (Iceland)

The molecular structure of urea in which a carbonyl group (carbon doubled bonded oxygen) is joined by two amine groups at each end.
Figure 26.5e. The molecular structure of urea (credit: Image by NEUROtiker, PDM).

Hakarl is a fermented Greenland shark, which is the national dish of Iceland. The process of fermenting the shark is essential as fresh shark meat is poisonous as it contains urea (Figure 26.5e.) and trimethylamine oxide.  See the Day 13: Iceland: Hákarl infographic for further information.

Physical Properties of Amides

With the exception of formamide (HCONH2), which is a liquid, all simple amides are solids (Table 26.5a.). The lower members of the series are soluble in water, with borderline solubility occurring in those that have five or six carbon atoms. Like the esters, solutions of amides in water usually are neutral—neither acidic nor basic.

Table 26.5a. Physical Constants of Some Unsubstituted Amides
Condensed Structural Formula Name Melting Point (°C) Boiling Point (°C) Solubility in Water
HCONH2 formamide 2 193 soluble
CH3CONH2 acetamide 82 222 soluble
CH3CH2CONH2 propionamide 81 213 soluble
CH3CH2CH2CONH2 butyramide 115 216 soluble
C6H5CONH2 benzamide 132 290 slightly soluble

Source: “15.14: Physical Properties of Amides” In Basics of GOB Chemistry (Ball et al.), CC BY-NC-SA 4.0.

The amides generally have high boiling points and melting points. These characteristics and their solubility in water result from the polar nature of the amide group and hydrogen bonding (Figure 26.5f.). (Similar hydrogen bonding plays a critical role in determining the structure and properties of proteins, deoxyribonucleic acid [DNA], ribonucleic acid [RNA], and other giant molecules so important to life processes.

Images represent hydrogen bonding in amides. Hydrogen bonding is shown by a dotted line between the hydrogen that is connect to the nitrogen within the amide to the oxygen from the water molecule.
Figure 26.5f. Hydrogen Bonding in Amides. Amide molecules can engage in hydrogen bonding with water molecules (a). Those amides with a hydrogen atom on the nitrogen atom can also engage in hydrogen bonding (b). Both hydrogen bonding networks extend in all directions. (Credit: Intro Chem: GOB (V. 1.0)., CC BY-NC-SA 3.0, edited by (Ball et al.), CC BY-NC-SA 4.0)

Spotlight on Everyday Chemistry: Urea

Urea (CO(NH2)2) is a diamide containing two amide groups joined by a carbonyl functional group. Urea is the main component of urine consisting of nitrogenous waste products from the metabolic breakdown of proteins. The liver produces enzymes which form urea which is then transported to the kidney’s for removal from the body. Urea a colourless, odourless solid which is highly soluble in water and when dissolved in water is neither acidic nor alkaline. Urea is widely used in fertilizers as a nitrogen source and is an important raw material for chemical industry.

The molecular structure of urea in which a carbonyl group (carbon doubled bonded oxygen) is joined by two amine groups at each end.
Figure 26.5g. The molecular structure of urea. (credit: Image by NEUROtiker, PDM).

Attribution & References

Except where otherwise noted, this page is adapted by Caryn Fahey from:

References cited in-text

National Center for Biotechnology Information (2024). PubChem Compound Summary for CID 11959, N-Ethylbenzamide. Retrieved February 7, 2024.

National Center for Biotechnology Information (2024). PubChem Compound Summary for CID 28774, N-Methylbutyramide. Retrieved February 7, 2024

  1. a. pentanamide, b. 3-chloropentanamide, c. N-ethylbenzamide

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  2. a. acetamide (or ethanamide IUPAC), b. N-methylbutanamide

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definition

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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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