What is an Amide?

A derivative is a compound that has been arisen from a similar compound by a chemical reaction. Amines are the functional groups that have been driven from ammonia. Amides are driven from carboxylic acid. Let’s discuss our main question: what is an amide? An amide is a functional group derived from ammonia. The amide group contains a carboxyl group and one nitrogen group. The amide formula is R-C(O)-N-H2, R-C(O)-N-R2, and R-C(O)-N-HR.

Some examples of amides are acetamide, benzamide, and diethylformmide. 

Structure of Amide

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Amides are composed of one nitrogen, one carbonyl group carbon, one oxygen atom, and a variable number of hydrogen and carbon atoms. The hybridisation of carbonyl carbon is sp2 and the hybridization of nitrogen in the amide group is sp2. The Sp2 hybridization is due to the resonance. The sp2 hybridisation attains the planar structure of the nitrogen bond.  In the amide structure, one lone pair is present on the nitrogen group. In an amide structure, the oxygen atom is attached to the carbon by two double bonds. The lone pair and carbonyl group are arranged in an alternate manner. This contributes to the resonance in the molecule. The presence of a double bond restricts the rotation about the nitrogen linkage. 

Resonance in Amides

The oxygen present in the carbon is more electronegative than carbon. Therefore, it attracts electrons from the bonded pair of electrons. The lone pair present on the nitrogen group is delocalised to the carbonyl group. This leads to the formation of the partial double bond between carbon and nitrogen. The oxygen, carbon, and nitrogen atoms have molecular orbitals that are occupied by the delocalised electrons. This whole bonding system together forms a conjugate system. Therefore, the three bonds of the nitrogen in the amide group are not pyramidal, like that of amines, but planar.

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Properties of Amides

Physical Properties of Amides:

  1. Except for formamide, all other amides generally exist in solid-state. Formamide exists in a liquid state.

  2. The amides with a low carbon number are water-soluble. 

  3. The boiling point of amides is generally high.

  4. The melting point of amides is generally high.

  5. Amides are polar in nature.

  6. Amides generally form hydrogen bonding.

Chemical Properties of Amides:

  1. The lone pair present on the nitrogen contributes to the resonance.

  2. Amides exhibit Planner restriction.

  3. Amides are slightly basic in nature. They are weaker than the amines.

  4. Due to the presence of a highly electronegative element in the amide group, they exhibit hydrogen bonding.

  5. Amides undergo various reactions like Hofmann rearrangement reaction, amide reduction reaction, Vilsmeier- Haack reaction.

  6. Bischier- Napieralski reaction.

  7. Hydrolysis- When boiled with water, acids, or alkalies. The reaction with water is slow, rapid with acids and very rapid with alkalies. When hydrolysed with water or acids, the products obtained are carboxylic acids and free ammonia. 

  8. Dehydration- On heating with a dehydrating agent like P2O5, POCl3, and SOCl2, amides lose a molecule of water to form nitriles (cyanides).

Types of Amides:

  1. Primary Amide- 

In primary amide two hydrogen atoms are attached with the nitrogen. Its general formula is R-C(O)-NH2

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  1. Secondary Amides- 

In secondary amide one hydrogen atoms are attached with the nitrogen. Its general formula is R-C(O)-NH-R.

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  1. Tertiary Amides- 

In tertiary amide, no hydrogen is attached to the nitrogen. Its general formula is R-C(O)-N-R2.

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Uses of Amides

  1. Amides are used for the preparation of primary amines.

  2. Certain amides such as dimethylformamide (DMF) and dimethylacetamide (DMA) are used as solvents for polar and non-polar compounds.

Preparation of Amides

Amides can be prepared by any of the following methods:

  1. By Ammonolysis of Acid Derivatives- 

Acyl chlorides, anhydrides, and esters on treatment with conc. Ammonia at ordinary temperature yield amides.

  1. By Thermal Decomposition of Ammonium Carboxylates- 

Ammonium carboxylates on healing lose a molecule of water to form amides.

  1. By Partial Hydrolysis of Cyanides- 

Amides can also be prepared by the partial hydrolysis of alkyl or aryl cyanides with cold conc. Hydrochloric acid

Qualitative Test for Amide

  1. Burning Test- 

When amide group is heated to an open flame, it burns without soot and leaves a white residue.

  1. Test with an Alkali

When amide is heated with sodium hydroxide, it gives the ammoniacal smell.

  1. Nitrous Acid Test

When amide is heated with hydrochloric acid and sodium nitrite, it gives effervescence due to the evolution of nitrogen.

Did You Know?

  • Formamide is the first member of the amide family.

  • Amides are the derivative of carboxylic acid.

  • Amides are used as intermediates for plastics production.

FAQs (Frequently Asked Questions)

Question: What is an Amide?

Answer: Amides are an acid derivative compound, composed of nitrogen, carboxylic group, and alkyl groups.

Question: What are the Chemical Properties of Amides?

Answer: The chemical properties of amides are given below:

  • The amide group exhibits resonance due to the presence of a lone pair on the nitrogen.

  • Due to the partial double bond, amides exhibit planner restriction.

  • Amides are amphoteric in nature, acting as both acid and base. 

  • The presence of a high electronegative element (oxygen) in the amide group, amides participate in the hydrogen bonding.

  • Amides undergo several chemical reactions. These chemical reactions include Hofmann rearrangement reaction, amide reduction reaction, Vilsmeier- Haack reaction.

  • Hydrolysis Reaction- - When amides heated with water, acids, or alkalies, it gives a hydrolysis reaction and forms carboxylic acids and free ammonia as a product. 

  • Dehydration- Amides gives dehydration reaction on heating with a dehydrating agent like phosphorus pentoxide (P2O5), Phosphorus trichloride POCl3, and sulfonyl dichloride SOCl2, amides lose a molecule of water to form nitriles (cyanides).