Amides: structure, nomenclature, reactions, examples –

To the amides are organic compounds characterized by presence of a nitrogen (N) attached directly to a carbonyl (C=O). They are naturally available substances, one of them is in the excreta of mammals (urea), but they can also be obtained by artificial synthesis.

Amides can be produced, for example, by ammonium salt dehydration, a process used in the manufacture of polymers. They are also used as fertilizers, due to its nitrogen availability, and as medicine, having antimicrobial action.

Read more: Acrylamide – amide that can be formed by heating some foods

Topics of this article

structure of amides

Amides are formed by a nitrogen bonded directly to a carbonyl or acyl group (RC=O). The double bond between carbon and oxygen and the possibility of moving this couple to nitrogen give the molecule planar geometryunlike amines, which have pyramidal geometry.

Don’t stop now… There’s more after the publicity 😉

Classification of amides

• Classification according to the number of organic substituents

Like amines, amides are classified according to the number of organic radical substituents that nitrogen hashowever, for amides, we have to consider that one of the ligands of the group must be the acyl group, that is, we will only have amides of the type:

• Unsubstituted amide: It has nitrogen bonded to two hydrogens and a carbonyl group.

Example:

• Monosubstituted amine: It has nitrogen bonded to a hydrogen, a carbonyl group and an organic radical. In this case, in which one of the hydrogens has been replaced by a carbon chain, consider R as an organic group.

Example:

• Disubstituted amine: It has nitrogen linked to two organic radicals and a carbonyl. In this case, the two hydrogens were replaced by carbon chains.

Example:

See too: How to classify organic halides?

• Classification according to the number of carbonyls attached to nitrogen

Amides can also be classified according to the number of carbonyls attached directly to the nitrogen in the molecule.

• primary amides: only one acyl group linked to nitrogen (R-CO)NH2 .
• secondary amides: two carbonyls or acyl group attached to nitrogen (R-CO)2NH.
• tertiary amides: three acyl groups linked to nitrogen (R-CO)3N.

Nomenclature of amides

The nomenclature for amides will be given by:

See the chart below:

The carbon count should start from the side closest to the nitrogen of the functional group.

Examples:

Amines may also receive a specification on the classification of the molecule in their nomenclature:

Remembering that nomenclature for radicals is formed by: Pprefix indicating number of carbons + “il” or “ila” ending. The radicals are positioned in the nomenclature in alphabetical order.

Examples:

Also access: Nomenclature of cyclic and branched hydrocarbons

Amides properties

• High melting and boiling point, which will have a scaled value according to the size and spatial arrangement of the carbon chain.
• Highly polar, due to the presence of carbonyl and nitrogen.
• Unsubstituted and monosubstituted amides carry out hydrogen bonding.
• Smaller, simpler molecules are soluble in water. The size of the molecule also interferes with the solubility of amides: the longer the carbon chain, the less soluble they are in water.
• Amides are basic due to their propensity to accept H+ ions.

Application of amides

• Used as intermediaries in the manufacture of polyethylene such as nylon.
• Applied in the formulation of drugs such as sulfanilamide and penicillin, active principles of bactericidal drugs in the control of infections.
• Urea, which can be obtained synthetically or as a product excreted by mammals, is a substance of the amide group, a diamide. It is used as a food supplement in agriculture and as a fertilizer.

Obtaining the amides

Amides are easily found naturally, but their synthesis is still widely used in industrial processes. See, below, some amide production reactions based on other nitrogenous compounds.

• Ammonium salt dehydration reaction

• Reaction of amines with acid chloride

• Reaction of anhydrides with amines

• Reaction of esters with amines

• Structural rearrangement of an aldoxime

• hydration of nitriles

Read also: Hydrolysis of amides – reaction used to obtain important substances

solved exercises

Question 1 – (UFRS) Aspartame, represented below, is an artificial sweetener used in many soft drinks and low-calorie foods.

The group framed in the figure is characteristic of the organic function
A) ester.
B) amide.
C) amino acid.
D) amine.
E) carbohydrate.

Resolution

Alternative B. The functional group selected in the figure is an amide, due to the presence of a carbonyl (C=O) linked directly to nitrogen (N).

Question 2 – (UNESP) In August 2005, the apprehension of batches of lidocaine that would have caused the death of several people in Brazil, due to manufacturing problems, was reported. This drug is a local anesthetic widely used in endoscopic examinations, reducing patient discomfort. Its molecular structure is shown below:

and presents the functions:
A) secondary amine and tertiary amine.
B) amide and tertiary amine.
C) amide and ester.
D) ester and tertiary amine.
E) ester and secondary amine.

Resolution

Alternative B.

After selecting and numbering the characteristic parts of each organic function, let’s analyze each one:
1- It is an AMIDE due to the presence of the acyl group, (RC=O) linked directly to nitrogen, monosubstituted.
2- As we do not have the presence of the acyl group (RC=O), but only nitrogen directly linked to other carbons, in this group we have a TERTIARY AMINE, because all three hydrogens, previously linked to nitrogen, were replaced by organic groups .

By Laysa Bernardes Marques de Araújo
Chemistry teacher