When we talk about basicity, we're talking about how basic something is. In the world of chemistry, a chemical or compound is considered basic if it can accept protons and act as a Bronsted-Lowry base. But that's not all. We also have something called nucleophilicity, which is the ability of a chemical or compound to act as a nucleophile. A nucleophile is an electron-pair donor, which means it donates a pair of electrons to electron-poor sites during a chemical reaction.

Now, whether an amine is acting as a base or a nucleophile, it will always form a bond between the lone nitrogen pair and something else. Here's a quick rule of thumb: if the amine is bonding to a hydrogen ion, then it's acting as a base. If the amine is bonding to anything other than a hydrogen ion, then it's acting as a nucleophile. Understanding the basicity of amines is essential in chemistry. Hopefully, this article has helped shed some light on the subject!

Why do amines act as bases?

Amines are a special type of molecule that contains a lone pair of electrons on the nitrogen atom. This unique characteristic allows them to form dative covalent bonds, as we can learn more about in the Covalent Bond concept. When amines bond with hydrogen ions, they can become 'proton acceptors', which allows them to act as a weak base. For a molecule to act as a base, it must be able to react with acids, which are proton donors.

Amines can also form conjugate acids, which are formed when the amine accepts a proton from a hydrogen ion. This process creates a new molecule with an extra hydrogen ion, which makes it more acidic than the original amine. When small amines are mixed with water, they can form hydrogen bonds. These bonds can cause the amine to dissolve in water and create a basic solution. Amines can also react with copper (II) ions, which are found in Fehling's solution, a blue solution of copper (II) ions dissolved in sodium hydroxide. This reaction causes the solution to change color, which can be used to test for the presence of amines. Understanding the basicity of amines and their various reactions is important in chemistry, and we hope this article has helped you gain a better understanding of this topic. 

How strong are amines as bases?

Amines are a type of molecule that act as weak bases, which means they only partially dissociate in water. The strength of an amine's basicity depends on the type of amine, whether it is aromatic or aliphatic. The basic property of amines comes from the lone pair on the nitrogen, which allows them to 'accept' and bond with protons. The availability of the nitrogen's lone pair determines the strength of the base, with more available lone pairs making the amine a stronger base, and less available lone pairs making the amine a weaker base. The availability of the lone pair is affected by the electron density of the amine around the nitrogen atom. When the electron density is concentrated around the nitrogen atom, the lone pair becomes more available. This is why the type of amine affects the availability of the lone pair, and therefore the strength of the base. Understanding the basicity of amines is important in chemistry, and we hope this article has helped clarify this topic.

Benzene ring

Aromatic amines have a benzene ring bonded to the nitrogen. Benzene rings draw electrons towards them, shifting the electron density away from the nitrogen, and the lone pair from the nitrogen actually becomes 'partially delocalised' onto the ring. The lone pair will therefore be much less available, meaning aromatic amines have the weakest basicity.

Alkyl groups

Aliphatic amines have at least one alkyl group bonded to the nitrogen atom. Alkyl groups 'push' electrons onto the nitrogen, having the opposite effect to benzene. By pushing electrons onto the nitrogen, there is a higher electron density around the nitrogen which means the lone pair will be more available. Therefore, aliphatic amines are stronger bases than aromatic amines and ammonia.

Ammonia

The nitrogen atom in ammonia experiences no inductive or delocalised effect on its electrons. For this reason, ammonia sits in between aromatic and aliphatic amines when it comes to its basic strength.

Primary, secondary, and tertiary amines

The difference in basic strength between primary, secondary, and tertiary amines is a bit more complicated. In general, primary amines are always weaker than secondary and tertiary amines, but the difference between secondary and tertiary amines is also dependent on the state of matter.

In their gaseous states, tertiary amines are generally more basic than secondary amines because the electron density of the nitrogen atom is more concentrated due to the absence of hydrogen atoms on the nitrogen. However, when they are in an aqueous solution, the situation is reversed; secondary amines are stronger bases than tertiary amines. The reasons for this can be quite complex and are not necessary to understand at this level. Overall, understanding the basic strength of primary, secondary, and tertiary amines is important in chemistry, as it allows us to predict how these molecules will behave in different environments and reactions.

Which reactions involve amines as the nucleophile?

The lone pair of electrons on nitrogen allow amines to act as nucleophiles.

Nucleophilic substitution

Amines act as nucleophiles when they react with halogenoalkanes in a nucleophilic substitution reaction (See Halogenoalkanes and Nucleophilic Substitution Reactions for more information). In this reaction, the amine forms a covalent bond with a carbon atom and replaces the bonded halogen. The outcome of this reaction is a quaternary ammonium ion salt and an amine that has gained another organic group.

Nucleophilic addition-elimination

Amines can react with acyl chlorides or acid anhydrides in a nucleophilic addition-elimination reaction. When this happens, the amine forms an N-substituted amide and releases a byproduct. When reacting with acyl chlorides, the byproduct is hydrogen chloride gas, and when reacting with acid anhydrides, the byproduct is a carboxylic acid. This reaction is important in organic chemistry because it allows us to synthesize amides, which are important functional groups found in many biologically active compounds. The reaction between amines and acyl chlorides or acid anhydrides is an example of how a nucleophilic reaction can be used to form new chemical bonds. Overall, understanding the reactions of amines with different organic molecules is important in organic chemistry, as it allows us to predict how these molecules will behave in different environments and reactions.

Amines Basicity

How does basicity affect nucleophilicity?

Basicity and nucleophilicity affect each other in the same way: as basicity increases, so does nucleophilicity, and as basicity decreases, so does nucleophilicity.

Is nucleophilicity directly proportional to basicity?

Yes, in general, nucleophilicity and basicity are directly proportional.

What is the meaning of nucleophilicity?

The meaning of nucleophilicity is a measure of how strong of a nucleophile a chemical or compound is. A higher nucleophilicity means a stronger nucleophile.

What is the difference between a base and a nucleophile?

The difference between a base and a nucleophile is to do with the chemicals they attack. While a nucleophile attacks electron-deficient areas around carbons atoms, a base attacks electron-deficient hydrogen atoms. In most cases, if something is a nucleophile then it is also a base.

How can we define basicity?

We can define basicity by thinking about how many protons any particular base is able to accept. If a base is simply a proton acceptor, then the more protons it can accept, the stronger its basicity.

‍