Chemical dyes, proteins, and even the hormone serotonin have something in common - they're all considered amines! In this article, we're going to dive into the world of organic chemistry and explore what amines really are. First, we'll take a look at the amine functional group. Then, we'll teach you how to classify amines and learn their formulae. We'll also cover amine nomenclature, so you can try your hand at naming different amines. Finally, we'll discuss the various properties and uses of amines. So, let's get started!

What are Amines?

An amine is an organic derivative of ammonia, in which one or more of the hydrogen atoms has been replaced by a hydrocarbon group. Here's ammonia. It consists of a nitrogen atom chemically bonded to three hydrogen atoms by single covalent bonds. The nitrogen atom also has a lone pair of electrons.

‍

If we replace one or more of the hydrogen atoms with an organic hydrocarbon group, we get an amine. Here's an example. A hydrogen atom has been swapped with a methyl group, forming methylamine. Don't worry – we'll look at how to name amines a little later on.

‍

Amine functional group

The functional group of an amine is characterized by a nitrogen atom with a lone pair of electrons, covalently bonded to at least one organic hydrocarbon group. We represent the organic group using the letter R. Here's a diagram of the functional group.

‍

Different types of Amines

As we mentioned earlier, amines are actually ammonia derivatives where one or more hydrogen atoms have been swapped out for an organic hydrocarbon group. These amines can be categorized as primary, secondary, or tertiary depending on the number of organic groups bonded to the nitrogen atom. Here are the general formulae for each type:

• Primary amines: NH2R (one hydrogen atom replaced by an organic group)
• Secondary amines: NHR2 (two hydrogen atoms replaced by organic groups)
• Tertiary amines: NR3 (all three hydrogen atoms replaced by organic groups)

These classifications and formulae are important to understand as they play a significant role in determining the properties and uses of specific amines.

‍

‍

Remember how we said that the nitrogen atom in an amine has a lone pair of electrons? Amines can use this pair to form a fourth bond with another organic group. This turns the amine into a quaternary ammonium ion, which has the affectionate nickname of 'quat'. Quaternary ammonium ions have a permanent positive charge and are readily turned into quaternary ammonium salts, which have a variety of uses. For example, they're found in products ranging from disinfectants to hair softeners.

‍

If you're interested in learning more about the various applications of amines, be sure to check out our article on the topic. In the meantime, it's worth noting that amines can be further categorized as either aliphatic or aromatic. Essentially, this depends on whether or not the amine contains a benzene ring.

For aromatic amines, at least one of the organic groups bonded to the nitrogen atom includes a benzene ring. In contrast, aliphatic amines have organic groups that are made up entirely of aliphatic chains and do not contain any benzene rings. This distinction is important, as it can have a significant impact on the chemical and physical properties of the amine in question.

‍

Naming Amines

Amines can be tricky to name because there are several different naming systems in use. However, one commonly-used method involves using the suffix "-amine" or the prefix "amino-" to indicate the presence of the amine functional group. Here are some key rules to keep in mind when naming amines:

• If there is only one amine group in the molecule, use the suffix "-amine."
• If there are multiple amine groups or other functional groups present, use the prefix "amino-."
• Use alkyl prefixes ending in "-yl" to indicate any alkyl groups attached to the nitrogen atom.
• Use root names to indicate the longest carbon chain in the molecule and numbers to indicate the position of any functional groups.

Let's practice this method with some examples:

• CH3CH2NH2: This molecule contains a single amine group, so we use the suffix "-amine." The alkyl group attached to the nitrogen atom is ethyl, so the name of this compound is ethylamine.
• CH3NHCH2CH3: This molecule contains a single amine group and two alkyl groups. The longest carbon chain is three carbons long, so the root name is "propane." We indicate the position of the amine group using the number 2, so the name of this compound is 2-propylamine.
• CH3NHCH(CH3)CH2CH3: This molecule contains a single amine group and several alkyl groups. The longest carbon chain is five carbons long, so the root name is "pentane." We indicate the position of the amine group using the number 2, so the name of this compound is 2-(1-methylethyl)amino-pentane.

Examples of amines

‍

First of all, let's find the amine group. We've highlighted it in blue. There's just one, so we use the suffix -amine. Next, identify any alkyl groups attached to the nitrogen atom. Here, there's just one methyl group, which we've highlighted in green. We use the prefix methyl-. This molecule's full name is therefore methylamine.

‍

Here's another example.

‍

Once again, this molecule has just one amine group, shown in blue. We therefore use the suffix -amine. But this time, there are three carbon chains attached to the nitrogen atom: two methyl groups, shown in green, and one ethyl group, shown in yellow. We show them using the prefixes methyl- and ethyl-, listing them in alphabetical order. But to show that there are two methyl groups present, we precede methyl- with a quantifier, di-. Putting this all together, we get the name ethyldimethylamine.

Finally, let's take a look at an amine with multiple functional groups.

‍

You can see that there are not only two amine groups but also a hydroxyl group, shown in pink. We therefore need to use the prefix amino- with the quantifier di-. To show the hydroxyl group, we use the suffix -ol. The carbon chain is three carbon atoms long, shown in green, and so we use the root name -prop-. To show the position of the functional groups, we use numbers. Here, the hydroxyl group takes priority, and so we call the carbon it is attached to ‘carbon 1’. This means that the amine groups are found on carbons 2 and 3. The full name of this molecule is therefore 2,3-diaminopropan-1-ol.

‍

If another functional group is present, you always use the prefix -amino alongside the suffix of the other functional group. The only exception to this rule is if the other functional group is a halogen. In this case, you carry on using the suffix -amine and instead use the prefix for the halogen.For more on nomenclature, check out Naming Conventions.

Properties of Amines

Now that we've learned how to name amines, let's focus on some of their properties.

Polarity

Amines are polar molecules. This is because nitrogen is more electronegative than both carbon and hydrogen. The nitrogen atom becomes partially negatively charged while the carbon and hydrogen atoms become partially positively charged.

‍

Melting and boiling points

Primary and secondary amines have high melting and boiling points compared to similar-sized alkanes. Because the nitrogen atom not only has a lone pair of electrons but is also attached to a hydrogen atom, it can form hydrogen bonds between molecules. These are the strongest type of intermolecular forces and require a fair amount of energy to overcome.

‍

The boiling points of primary, secondary, and tertiary amines can vary due to differences in intermolecular forces. Secondary amines have slightly lower boiling points than primary amines because the nitrogen atom is located between two organic groups, which reduces the strength of the permanent dipole between nitrogen and hydrogen. This weaker dipole results in weaker hydrogen bonding and lower boiling points. Tertiary amines have much lower melting and boiling points than primary and secondary amines because all three hydrogen atoms on the nitrogen atom are replaced by organic hydrocarbon groups. This means that the molecule cannot form hydrogen bonds, resulting in weaker intermolecular forces and lower boiling points.

When it comes to solubility, short-chain amines, including tertiary amines, are generally soluble in water because they can form hydrogen bonds with water molecules. However, tertiary amines can only form one hydrogen bond with water due to the lack of hydrogen atoms on the nitrogen atom. As the size of the amine increases, the insoluble hydrocarbon chains start to interfere with and disrupt the hydrogen bonding with water molecules, resulting in decreased solubility. Longer-chain amines are typically insoluble.

‍

Amines have a trigonal pyramidal shape with nitrogen at the apex. The bond angles between the attached groups are 107°.

‍

Not sure where this shape and bond angle have come from? Shapes of Molecules has got you covered.

Basicity

Amines can act as both weak Bronsted-Lowry bases and Lewis bases due to the presence of a lone pair of electrons on the nitrogen atom. Primary amines are better Bronsted-Lowry bases than ammonia because the alkyl group bonded to the nitrogen atom is electron-releasing and increases the availability of the lone pair of electrons, making it more appealing to protons. Secondary amines are even better bases than primary amines because they have two alkyl groups, which further increase the availability of the lone pair of electrons.

Tertiary amines are the best bases as gases, but they are less soluble in aqueous solution than secondary amines, making them less effective at picking up a proton in solution. The strength of different amines as bases can be studied in more detail in the article "Amines Basicity."

Uses of Amines

Amines have various uses in different fields. In the human body, amines are essential components of proteins and neurotransmitters. Many painkillers, including morphine and novocaine, are amines. Amines are also used in removing carbon dioxide from flue gases and in the production of various insecticides, pesticides, and disinfectants.

Apart from these, amines are also used in the production of dyes, rubber, and plastic materials. They are used as intermediates in the manufacturing of pharmaceuticals, agrochemicals, and other organic chemicals. Amines are also used as solvents, curing agents, and fuel additives. Overall, amines have a wide range of applications in different industries due to their diverse chemical properties and reactivity.

Amines - Key takeaways

That's correct! Amines are organic compounds that are derivatives of ammonia, where one or more hydrogen atoms have been replaced by a hydrocarbon group. They can be classified as primary, secondary, or tertiary depending on the number of hydrogen atoms replaced by organic groups.

Amines can also be classified as aliphatic or aromatic depending on whether they are bonded to aliphatic or benzene ring organic groups. Amines have polar characteristics, and their physical properties such as melting and boiling points and solubility in water depend on their molecular structures. Amines are also weak bases, and their relative strength as bases depends on the availability of the lone pair of electrons on the nitrogen atom. As you mentioned earlier, amines play crucial roles in the body, drugs, and disinfectants, among other applications due to their diverse chemical properties and reactivity.

Amines

What is an amine?

An amine is an organic derivative of ammonia, meaning one or more of ammonia's hydrogen atoms is replaced with an organic group.

How do you name amines?

You typically name amines using the suffix -amine. However, if there is more than one amine group or any other functional group present, you use the prefix -amino. 

What is the formula for an amine?

The formula for an amine depends on the type of amine you are dealing with. Primary amines have the general formula NH2R, secondary amines have the general formula NHR2 and tertiary amines have the general formula NHR3.

What are some examples of amines?

Examples of amines include amino acids, which make up all of the proteins in our body.

How do you identify an amine?

Amines can be identified by their functional group, which contains a nitrogen atom with a lone pair of electrons bonded to at least one organic group.

‍