Did you know that the drug paracetamol, the fibre nylon, and the proteins in your muscles all have something in common? They are all examples of amides! In this article, we will be exploring amides in organic chemistry. First, let's define what amides are and take a look at their functional group, general formula, and structure. Then, we'll dive into amide nomenclature and learn how to produce amides. We will also explore some of their reactions and provide examples and uses of amides. Keep reading to become an amide expert!

What are amides?

If you've studied organic chemistry before, you may be familiar with amines. These are organic molecules that contain the amine functional group, -NH2. Amides are similar molecules that also contain the amine group, -NH2, but it's bonded to the carbonyl group, C=O. This is what's known as the amide functional group, which gives amides their unique chemical properties. To be more specific, amides are organic molecules that have the amide functional group, -CONH2. This group consists of a carbonyl group bonded to an amine group. If you want to learn more about amines and the carbonyl group, be sure to check out our articles on those topics for a deeper understanding.

Amide general formula

As we've learned, amides have a general formula of RCONH2, where R represents an organic group connected to the carbonyl group. This formula specifically refers to primary amides. However, there are also secondary and tertiary amides, which are also called N-substituted amides. In secondary and tertiary amides, one or both of the hydrogen atoms attached to the nitrogen atom are replaced by other organic R groups. This gives secondary amides the general formula RCONR'H and tertiary amides the formula RCONR'R''. For the purposes of this article, we will mainly be focusing on primary amides.

Amide structure

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

‍

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.

‍

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.

‍

The process of naming primary amides involves several steps. First, we identify the carbon atom in the carbonyl group as carbon 1, and then we find the length of the longest carbon chain, which gives us the root name of the molecule. We then use prefixes and numbers to indicate any side chains or additional functional groups, and we finish off the name with the suffix -amide.

For example, let's apply these rules to the molecule RCONH2. If we take the longest carbon chain and count the number of carbon atoms, we get the root name of the molecule. If there are any side chains or additional functional groups, we show them using prefixes and numbers. Finally, we add the suffix -amide to indicate that the molecule is an amide. For instance, let's consider the molecule 2-methylpropanamide. The longest carbon chain in this molecule is three carbon atoms long, which 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. Thus, the final name of the molecule is 2-methylpropanamide.

‍

‍

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.

‍

To name an amide, we first identify the longest carbon chain in the molecule and use it to determine the root name, which is followed by the suffix -amide. If there are any side chains or functional groups, we indicate them using prefixes and numbers.

For example, consider the molecule with the formula CH3CH2CONHCH3. The longest carbon chain is three carbon atoms long, giving it the root name -propan-. There is also a methyl group attached to the nitrogen atom, which we show using the prefix N-methyl-. Therefore, the name of this molecule is N-methylpropanamide.

Moving on to the production of amides, there are two similar reactions that can be used. The first is a nucleophilic addition-elimination reaction between an acyl chloride and ammonia. The second is a nucleophilic addition-elimination reaction between an acyl chloride and a primary amine. The mechanism for these reactions is more thoroughly explained in the process of acylation.

Amide: Acyl chloride and ammonia

That's correct! The reaction between an acyl chloride and ammonia (NH3) is a nucleophilic addition-elimination reaction, which results in the production of a primary amide and ammonium chloride. This reaction is also considered a condensation reaction because it releases a small molecule, in this case, hydrochloric acid (HCl).

For instance, let's take the reaction between ethanoyl chloride (CH3COCl) and ammonia (NH3). When these two compounds react, they form ethanamide (CH3CONH2) and hydrochloric acid (HCl). The hydrochloric acid that is produced then reacts with another molecule of ammonia to form ammonium chloride (NH4Cl).

Overall, the reaction can be represented by the following equation:

CH3COCl + NH3 → CH3CONH2 + HCl
HCl + NH3 → NH4Cl

This reaction is an important way to produce primary amides in the laboratory and in industry.

Amide: Acyl chloride and primary amine

That's correct! When an acyl chloride reacts with a primary amine, a secondary amide or an N-substituted amide is produced, along with hydrochloric acid (HCl) and an ammonium salt. This reaction is also a nucleophilic addition-elimination reaction and a condensation reaction. Similarly, the reaction between an acyl chloride and a tertiary amine produces an amide with two N-substitutes.

Another method for producing amides is through the reaction between a carboxylic acid and either ammonia or an amine. However, this method is slower and less efficient than the reaction between an acyl chloride and an amine. As for the reactions of amides, they can undergo hydrolysis with an aqueous acid or alkali, which breaks down the amide bond to produce a carboxylic acid and either ammonia or an amine. Amides can also be reduced with LiAlH4 to produce a primary amine. In terms of their basicity, amides are weak bases due to the presence of the carbonyl group and the resonance stabilization of the lone pair of electrons on the nitrogen atom.

Amide: Hydrolysis with aqueous acid or alkali

When an amide is reacted with an aqueous acid or alkali, it undergoes hydrolysis and breaks down into a carboxylic acid and either ammonia or an amine, depending on the type of amide. This reaction requires heating and can be used to test for the presence of amides.

If an acid is used, it reacts with the ammonia or amine produced to form an ammonium salt. If an alkali is used, it reacts with the carboxylic acid produced to form a carboxylate salt.

For example, heating ethanamide (CH3CONH2) with aqueous hydrochloric acid (HCl) produces ethanoic acid (CH3COOH) and ammonia (NH3), which further reacts to form ammonium chloride (NH4Cl). On the other hand, heating ethanamide with aqueous sodium hydroxide (NaOH) produces ethanoic acid and ammonia, and the ethanoic acid further reacts to form sodium ethanoate (CH3COONa). This reaction is a useful way to break down amides into their constituent parts and is commonly used in the laboratory.

Amide: Reduction with LiAlH4

That's correct! When an amide is reduced using a strong reducing agent like lithium tetrahydridoaluminate (LiAlH4), the oxygen atom in the carbonyl group is replaced by two hydrogen atoms. This reaction produces an amine and water and takes place at room temperature in dry ether. For instance, reducing methanamide (HCONH2) with LiAlH4 produces methylamine (CH3NH2) and water. This reaction is useful for synthesizing amines from amides in the laboratory. 

Amide: Basicity

Excellent! Amines act as weak bases due to the lone pair of electrons on the nitrogen atom in their amine group, but amides aren't basic because the carbonyl group in amides draws electron density towards itself, reducing the attractive strength of nitrogen's lone pair of electrons.

Amides have a wide range of applications in real life. For instance, proteins, plastics, synthetic fibers like nylon and Kevlar, and natural fibers like silk and wool are all polyamides. They play a crucial role in the pharmaceutical industry as well, with amides like paracetamol, penicillin, and LSD being commonly used. Urea, an organic molecule excreted in urine, is another significant amide that is produced industrially for use in fertilizers and animal feeds. By now, you should be able to define amides, describe their general formula and structure, explain how they are formed and how they react, and name some common examples of amides.

Amide - Key takeaways

Great job! Your description of amides is spot on. They have a carbonyl group (C=O) bonded to an amine group (-NH2) and can be primary, secondary, or tertiary. Secondary and tertiary amides are also called N-substituted amides. Amides are named using the suffix -amide and 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. Dehydrating amides using LiAlH4 leads to the formation of an amine and water. Some common examples of amides include proteins, paracetamol, and nylon.

Amide

How are amides formed?

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.

What are some examples of amides?

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

What are amides used for?

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.

What are the three types of 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.

What is an amide vs an amine?

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.

‍