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What are amides?

Amides are a type of organic compound that is formed by the union between a carboxylic acid and an amine. They are also called acidic amines and that is precisely where the word amide comes from .

These compounds are very important for life, since they are an essential part of proteins, peptides and some hormones. They are also part of the nitrogenous bases of DNA and RNA, which contain our genetic information.

Amides are also very important in industry. For example, nylon is one of the most widely used synthetic fibers in the world and is made up of a long chain of amides joined one after another.

Also, amides are widely used in the pharmaceutical industry, as they are part of drugs such as lidocaine.

  • Almost all are solid: all amides are solid at room temperature, except the smallest and simplest which is formamide. The latter is liquid.
  • They have high boiling points: Compared to carboxylic acids and the amines of which they are made, amides have a high boiling point. For example, acetamide (CH 3 CONH 2 ) is formed by the union of acetic acid (vinegar) with ammonia. The boiling point of acetamide is 221.2ºC, while that of acetic acid is 118ºC and that of ammonia is -33.34ºC.
  • Some are soluble in water: the smaller amides mix well with water, so they are easy to dissolve in it. However, as they get larger, they become less soluble.
  • They are less basic than amines: an amide is always less basic (or more acidic) than the amine from which it comes. In fact, the name comes from combining amide ami na + aci da .
  • Their bond is easily broken: if a strong base is added to them as a catalyst, the amides react quickly with water. This reaction is called hydrolysis, and during the reaction, the amide breaks down to form the original acid and amine.
  • They are colorless and odorless: in general, amides are substances that do not have a characteristic color or odor.

Functional group structure

Chemically, amide is a functional group that contains a carbonyl group (C = O) from a carboxylic acid, linked to a nitrogen from ammonia or an amine. The general structure of amides is:

A characteristic of the structure of amides that distinguishes them from amines is that the pair of free electrons that nitrogen possesses is shared with the carbonyl group through a process called resonance. This is what makes amides less basic than amines.

Types of amides

Depending on whether the acid is combined with ammonia, with a primary amine or with a secondary amine, three types of amides with different structures can be obtained:

Simple amides

They are formed by the union between a carboxylic acid and ammonia. This type of amide has a -NH 2 group attached to the carbonyl group. Simple amides can form several hydrogen bonds with each other and with water, so they are usually more soluble than substituted ones.

  • Examples of simple amides: formamide, acetamide and butyramide.

Substituted amides

They are obtained by the union of an acid and a primary amine. In this case, one of the hydrogens of the -NH 2 of the simple amides is substituted by an alkyl, and therefore they are called substituted amides.

  • Example of a substituted amide : the bond between amino acids in proteins.

Disubstituted amides

They come from the reaction between an acid and a secondary amine. In this case, both hydrogens of the -NH 2 group are substituted by alkyl groups. Disubstituted amides do not have hydrogens attached to nitrogens, so they cannot form hydrogen bonds with each other, and only a weak one with water. This makes them less soluble in water than the other classes of amides.

Lactams, primary, secondary and tertiary amides

Apart from the three types of amides just mentioned, there are also primary, secondary and tertiary amides , which differ by having one, two or three acyl groups attached to the nitrogen atom.

Finally, some amides form closed cycles. In this case, the compound is called lactam . Lactams are very important in nature. For example, uracil, which is part of RNA, is a lactam.

Nomenclature of amides

Simple amides

Simple amides are named after the carbon chain of the acid they come from (the main chain). The name is constructed by placing the prefix indicating the number of carbons (methane-, butan-, hexan-, etc.) or common name of the acid removing -oic or -ic termination (as in acet ic ) and adding the ending -amide.

  • Example: the amide that comes from acetic acid is called acetamide and the one that comes from propanoic acid is called propanamide.

Substituted and disubstituted amides

In this case, it begins by naming the alkyl groups that are attached to the nitrogen, preceded by the letter N-. The rest of the amide is then named as the main chain.

Example:

The rest of the main chain, the one with the amide functional group, has 10 carbon atoms. That is, your name must have the prefix decan- followed by the ending amide, or, decanamide. So the full name is N-isopropyldecanamide.

Examples of amides

  • Benzamide C 6 H 5 CONH 2
  • N, N-dimethylacetamide CH 3 CON (CH 3 ) 2
  • Acetamide CH 3 CONH 2
  • Phenylacetamide (C 6 H 5 ) CH 2 CONH 2
  • N-butyl-N-propylformamide HCON (C 3 H 7 ) (C 4 H 9 )
  • 4-hydroxybutanamide CH 2 (OH) CH 2 CH 2 CONH 2
  • Urea CO (NH 2 ) 2
  • Propanamide CH 3 CH 2 CONH 3
  • N-butyl-2-isopropylpentanamide CH 3 CH 2 CH 2 CH (C 3 H 7 ) CONH (C 4 H 9 )
  • N- (bromomethyl) undecanamide CH 3 (CH 2 ) 9 CONHCH 2 Br

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