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Amide

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Chemistry

Believe it or not, the drug paracetamol, the fibre nylon, and the proteins in your muscles have something in common: they are all examples of amides.

  • This article is about amides in organic chemistry.
  • We'll start by defining amides.
  • We'll be taking a look at their functional group, general formula, and structure.
  • We'll then find out about amide nomenclature.
  • After that, we'll look at how you produce amides before exploring some of their reactions.
  • Finally, we'll consider both examples and uses of amides.

What are amides?

In organic chemistry, you might have previously come across Amines. These are organic molecules with the amine functional group, -NH2. Amides are molecules that are similar to amines. They contain the amine group, -NH2, bonded to the carbonyl group, C=O. This is known as the amide functional group.

Amides are organic molecules with the amide functional group, -CONH2. This consists of a carbonyl group bonded to an amine group.

Check out Amines and The Carbonyl Group for more information about these two functional groups.

Amide general formula

We now know that amides contain a carbonyl group, C=O, bonded to an amine group, -NH2. This gives amides the general formula RCONH2. Here, R represents an organic group joined to the other side of the carbonyl group.

The general formula for an amide given above is actually the formula of a primary amide. You can also get secondary and tertiary amides, which are also known as N-substituted amides. In these cases, either one or both of the hydrogen atoms attached to the nitrogen atom are replaced by other organic R groups. This gives secondary and tertiary amides the general formulae RCONR'H and RCONR'R'', respectively. However, we'll be focusing mostly on primary amides.

Amide structure

Let's use our new knowledge of amides to draw their structure. Here is an example of an amide.

Amides amide structure StudySmarterThe structure of an amide. Anna Brewer, StudySmarter Original

Note the carbonyl group on the left, with its C=O double bond, and the amine group on the right. Because this is a primary amide, the nitrogen atom is bonded to two hydrogen atoms and no other R groups.

Amide polarity

We can expand on the structure of amides by showing their polarity. You might know that both the carbonyl and the amine group are polar. This makes amides polar as well. The carbon atom in the carbonyl group is always partially positively charged, whilst the oxygen atom is partially negatively charged. Meanwhile, the nitrogen atom in the amine group is partially negatively charged, whilst the hydrogen atoms are partially positively charged.

Amides amide structure polarity StudySmarterThe polarity of amides. Anna Brewer, StudySmarter Original

Naming amides

Moving on, let's look at amide nomenclature.

Primary amides

Naming primary amides is fairly simple. It all depends on the R group attached to the carbonyl group. In fact, it is very similar to naming carboxylic acids. Let's look at an example.

Name the following amide:

Amides nomenclature 2-methylpropanamide StudySmarterAn amide for you to name. Anna Brewer, StudySmarter Original

To name primary amides, we follow these steps.

  1. Taking the carbon atom in the carbonyl group as carbon 1, find the length of the longest carbon chain. This gives you the molecule's root name.
  2. Show any side chains or additional functional groups using prefixes and numbers.
  3. Finish it all off with the suffix -amide.

Applying these rules to our example above, we can see that the longest carbon chain is three carbon atoms long. This gives it the root name -propan. If we number the carbon atoms starting from the carbon in the carbonyl group, we can see that there is a methyl group attached to carbon 2. This gives us the final name of 2-methylpropanamide.

Amides nomenclature 2-methylpropanamide StudySmarter2-methylpropananmide. Anna Brewer, StudySmarter Original

Secondary and tertiary amides

You should remember from earlier in the article that secondary and tertiary amides have additional R groups attached to their nitrogen atom. To indicate these R groups, we use additional prefixes, indicated by the letter N-. Here's an example.

Name the following amide:

Amides nomenclature N-methylpropanamide StudySmarterAn amide for you to name. Anna Brewer, StudySmarter Original

Once again, the longest carbon chain is three carbon atoms long. This gives the amide the root name -propan-. There is also a methyl group attached to the nitrogen atom. We show this using the prefix methyl-, preceded by the letter N-. This molecule's name is therefore N-methylpropanamide.

Production of amides

Next, let's move on to look at the production of amides. You need to know about two similar reactions:

  • The nucleophilic addition-elimination reaction between an acyl chloride and ammonia.
  • The nucleophilic addition-elimination reaction between an acyl chloride and a primary amine.

The mechanism for these two reactions is covered in more depth in Acylation.

Acyl chloride and ammonia

Reacting an acyl chloride with ammonia (NH3) produces a primary amide and ammonium chloride. This is a nucleophilic addition-elimination reaction. It is also a condensation reaction, as it releases a small molecule in the process. Here, that small molecule is hydrochloric acid (HCl). The hydrochloric acid then reacts with another molecule of ammonia to form ammonium chloride (NH4Cl).

For example, reacting ethanoyl chloride (CH3COCl) with ammonia (NH3) produces ethanamide (CH3CONH2)and hydrochloric acid, which further reacts with another molecule of ammonia to form ammonium chloride (NH4Cl).

Acyl chloride and primary amine

Reacting an acyl chloride with a primary amine produces a secondary amide, also known as an N-substituted amide. Once again, this is an example of a nucleophilic addition-elimination reaction. It is also a condensation reaction, releasing hydrochloric acid in the process. The hydrochloric acid reacts with another molecule of the primary amine to form an ammonium salt.

For example, reacting ethanoyl chloride (CH3COCl) with methylamine (CH3NH2) produces N-methylethanamide (CH3CONHCH3) and methylammonium chloride (CH3NH3Cl):

In a similar way, reacting an acyl chloride with a tertiary amine produces an amide with two N-substitutes.

You can also produce amides in the reaction between a carboxylic acid and either ammonia or an amine. You first react the carboxylic acid with solid ammonium carbonate to produce an ammonium salt. This turns into an amide when you heat it. However, this method has several disadvantages. It is much slower than the reaction between an acyl chloride and either ammonia or an amine, and it doesn't go to completion. This results in a lower yield.

Reactions of amides

Wondering how amides react? Let's explore that next. You need to know about two different reactions.

  • Hydrolysis with an aqueous acid or alkali.
  • Reduction with LiAlH4.

We'll also touch on their basicity.

Hydrolysis with aqueous acid or alkali

First up, let's look at what happens when you react an amide with an aqueous acid or alkali. You actually produce a carboxylic acid and either ammonia or an amine, depending on whether your amide is primary, secondary, or tertiary. This is a hydrolysis reaction and requires heating. The acid or alkali then reacts with the products formed.

  • If you use an acid, the acid reacts with the ammonia or amine formed to produce an ammonium salt.
  • If you use an alkali, the alkali reacts with the carboxylic acid formed to produce a carboxylate salt.

Here are a couple of examples. Heating ethanamide (CH3CONH2) with aqueous hydrochloric acid (HCl) produces ethanoic acid (CH3COOH) and ammonia (NH3), which further reacts to form ammonium chloride (NH4Cl):

The hydrochloric acid acts as a catalyst in the first part of the reaction, as it isn't changed or used up in the reaction. However, it is involved in the second part of the reaction, when it turns ammonia into ammonium chloride.

Heating ethanamide with aqueous sodium hydroxide (NaOH) also produces ethanoic acid and ammonia. The ethanoic acid further reacts to form sodium ethanoate (CH3COONa):

Here, the amide reacts directly with the alkali. This means that, unlike in the reaction with acid that we saw above, the alkali is a reactant, not a catalyst.

You can use the reaction between an amide and an alkali to test for amides. Heating an amide with sodium hydroxide produces ammonia gas, which turns red litmus paper blue. It is also recognisable by its distinct pungent smell.

Reduction with LiAlH4

Next up, let's consider what happens when you reduce an amide using a strong reducing agent such as lithium tetrahydridoaluminate, LiAlH4. The reaction gets rid of the oxygen atom in the amide's carbonyl group and replaces it with two hydrogen atoms. This reaction takes place at room temperature in dry ether and also produces water.

For example, reducing methanamide (HCONH2) with LiAlH4 produces methylamine (CH3NH2) and water:

Basicity

You might know that amines act as weak bases. This is because the nitrogen atom in their amine group is able to pick up a hydrogen ion from solution using its lone pair of electrons. However, despite also containing an amine group, amides aren't basic. This is because they contain a carbonyl group, C=O. The carbonyl group is extremely electronegative and draws electron density towards it, reducing the attractive strength of nitrogen's lone pair of electrons. Therefore, amides don't act as bases.

Examples and uses of amides

Knowing what amides are and how they react is all well and good, but how does that apply to real life? Here are some examples of amides and their uses.

  • Proteins, from the keratin in your hair and nails to the enzymes catalysing your cellular reactions, are all polyamides. They are made up of lots of smaller monomer units, called amino acids, joined together by amide linkage groups.
  • Plastics and synthetic fibres such as nylon and Kevlar are also types of polyamides. So too are natural fibres like silk and wool.
  • They play a role in the pharmaceutical industry - paracetamol, penicillin, and LSD are all examples of amides.
  • The organic molecule urea, a natural waste product that we excrete in urine, is also an amide. It is produced industrially for use in fertilisers and animal feeds.

You should now feel confident at defining amides and giving their general formula and structure. You should be able to describe how they are formed, as well as how they react. Finally, you should be able to name some common examples of amides.

Amide - Key takeaways

  • Amides are organic molecules with the amide functional group. This consists of a carbonyl group (C=O) bonded to an amine group (-NH2).
  • Amides can be primary, secondary, or tertiary. We call secondary and tertiary amides N-substituted amides.
  • Amides are named using the suffix -amide.
  • Amides are formed in the reaction between an acyl chloride and either ammonia or a primary amine.
  • Amides react with aqueous acid to form a carboxylic acid and ammonium salt, and with aqueous alkali to form a carboxylate salt and ammonia.
  • Amides can be dehydrated using LiAlH4 to give an amine and water.
  • Common examples of amides include proteins, paracetamol, and nylon.

Amide

Amides are formed in the nucleophilic addition-elimination reaction between an acyl chloride and either ammonia or a primary amine. This is also a condensation reaction.

Examples of amides include proteins, paracetamol, urea, and nylon.

Amides are used in the pharmaceutical industry. They also make up all proteins and enzymes. In addition, many synthetic fibres such as nylon and Kevlar are made from amides.

Amides can be primary, secondary, or tertiary. Primary amides have the general formula RCONH2, secondary amides have the general formula RCONHR’ and tertiary amides have the general formula RCONR’R’’. Secondary and tertiary amides are also known as N-substituted amides.

Amines are molecules with the amine functional group, -NH2. Amides also have the amine functional group, but in this case it is directly bonded to a carbonyl group, C=O. This creates the amide functional group: -CONH2.

Final Amide Quiz

Question

What is an amide?

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Answer

Amides are organic molecules with the amide functional group, -CONH2.

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Question

Which two functional groups make up the amide group?

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Answer

The amine group, -NH2

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Question

Which of the following are amides?

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Answer

CH3CONH2

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Question

What is the general formula of a primary amide?

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Answer

RCONH2

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Question

What is the general formula of a secondary amide?

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Answer

RCONHR'

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Question

True or false? The nitrogen atom in the amide functional group is partially positively charged.

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Answer

False

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Question

What are the products of the reaction between an acyl chloride and ammonia?

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Answer

A primary amide and hydrochloric acid, which reacts further with ammonia to produce ammonium chloride.

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Question

What are the products of the reaction between an acyl chloride and primary amine? 

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Answer

A secondary amide and hydrochloric acid, which reacts further with the primary amine to produce an ammonium salt.

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Question

The reaction between an acyl chloride and ammonia is a _____ reaction

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Answer

Nucleophilic addition-elimination

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Question

What are the two methods of hydrolysing amides?

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Answer

Heating with aqueous acid or alkali.

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Question

Reacting an amide with aqueous acid gives ____.

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Answer

A carboxylic acid and ammonia, which reacts with the acid to form an ammonium salt.

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Question

Reacting an amide with aqueous alkali gives ____.

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Answer

A carboxylic acid and ammonia. The carboxylic acid reacts further with the alkali to form a carboxylate salt.

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Question

How do you test for amides?

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Answer

Add sodium hydroxide (NaOH). Ammonia gas will be given off, which turns red litmus paper blue.

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Question

How do you reduce amides?

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Answer

By reacting with a strong reducing agent such as LiAlH4 in dry ether.

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Question

Reducing amides produces ____.

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Answer

An amine and water.

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Question

Ethanamide is reduced. What are the products?

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Answer

Ethylamine and water

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Question

Give three examples of amines.

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Answer

  • Proteins
  • Enzymes
  • Kevlar
  • Nylon
  • Paracetamol
  • Urea

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