Amino Group: Definition And Examples

Amino groups are single functional groups comprised of a nitrogen atom linked to hydrogen atoms, aryl groups, alkyl groups or some combination of those structures. If an amino group is attached to an organic compound (compounds containing carbon) it is referred to as an amine.

The most notable amines are amino acids. An examination of the composition of amino groups, and the way they form structures such as amino acids, will help make amino groups clearer.

Defining Amino Groups/Amines

In chemistry, a functional group is a group of atoms which are responsible for certain reactions that the molecule may undergo, as well as specific properties of that molecule. Functional groups which contain a nitrogen atom linked by single bonds to alkyl groups, aryl groups, hydrogen groups, or some combination of these groups are called amino groups. An organic compound that is comprised of an amino group and other atoms is referred to as an amine.

Amines are derived from ammonia, chemical formula NH3. The H3 in NH3 means that there are three hydrogens in the molecule, and when at least one of these hydrogens is replaced by an aryl or alkyl group, an amine is formed. Primary amines are formed when one hydrogen is a place, secondary amines are formed when two hydrogens are placed, and tertiary amines are formed when all three hydrogens are replaced. Much like pure ammonia, amines easily coordinate with protons thanks to the presence of an unshared electron pair, and as such, they are considered weak bases. A fourth type of amine, cyclic amines, can be formed if the connectivity between substituents linked to the nitrogens is just right.

An example of the structure of a primary amine. Photo: By Kes47 (?) – File:Primary-amine-2D-general.png, Public Domain,

Amines follow a specific naming structure. An amine will be given either the suffix “-amine” or the prefix “amino”. If an “N-” is appended to the amine, it means that there is a substitution at the nitrogen atom. Organic compounds having different numbers of amino groups will be named differently to reflect this. An organic compound with two amino groups is referred to as a diamine, three amino groups make a triamine, four amino groups a tetramine, and so on.

In terms of the structure of amines, amines can have several different structures. Amines belonging to the alkyl group typically have tetrahedral nitrogen centers, meaning that there are bonds between nitrogen and atoms like carbon or hydrogen, with the nitrogen in the center. CNH and CNC bonds are said to be close to the idealized angle for tetrahedral bonds, the angle 109°. C-C bonds have slightly longer bond distances than C-N bonds. Some amines have a chiral, or mirror, structure. Amines which have the NRR’R” or NHRR’ structures are considered chiral, with the nitrogen atom in the center having four substituents. In the case of aromatic amines, the distance between the C-N bonds is approximately equivalent to the distance between the C-C bonds.

Properties Of Amines

Amines have several notable chemical properties. Mineral acids can bind with amines to form amine salt, such as occurs when hydrochloric acid bonds with an amine to form amine hydrochloride. Amines which are water insoluble can be made water-soluble by combining them with acid and creating an amine salt. Alkylammonium salts are formed when amines react with alkyl halides. Alkyl halides and ammonia can be combined together to create ammines, and this also has the effect of neutralizing the ammonium salt that results when the amine is formed. Synthesizing amines with this method will create compounds comprised of all three types of amines, primary, secondary, and tertiary. This mixture can be easily divided into the three different types of amines by using distillation.

Another way to produce amines is by reacting ammonia with any compound that has nitrogen in a substantially oxidized state, such as alcohol. Many different chemical reactions have amines as an ingredient, such as the creation of amides by the reaction of amines and esters, acid anhydrides, and acid chloride. Every reaction of an amine involves the bonding of amino-nitrogen to an electron-deficient atom, via the pathway of the amine’s free electron pair.

Important Amines


Aniline is a famous aromatic amine. Photo: By Ben Mills – Own work, Public Domain,

Anilines have the formula C6H5NH2, and as an aromatic amine, it has a pungent odor. The odor of aniline is often said to be like rotting fish or garbage. Aniline is often used in the creation of chemical precursors for use in the production of polyurethane and similar industrial compounds. Much is known about how aniline interacts with other compounds. When aniline oxidizes it typically results in the creation of new C-N bonds, although some reactions can be restricted to the nitrogen regions. If aniline oxidizes in an alkaline solution, azobenzene is created.

Reactions between aniline and chromic acid result in the creation of quinone while chlorates reacting with analine create aniline black, a material with high electrical potential. Reactions with acyl chlorides like acetyl chloride creates amides. Aniline is often used in the creation of chemicals to process rubber, the creation of pigments and dyes, and the creation of herbicides. Aniline can also be used to create certain pharmaceutical drugs, such as those using paracetamol, like acetaminophen.


Trimethylamine has the formula N(CH3)3 and it is a colorless, flammable, and hygroscopic chemical. The compound is an aromatic amine, similar to aniline, and much like aniline, it has a strong odor like fish when in low concentrations, though at higher concentrations it is said to have an older more like ammonia. At room temperature, trimethylamine is a gas. Trimethylamine often comes from the breakdown of organic material, but in humans gut microbiota can produce it by breaking down nutrients like carnitine and choline.

Trimethylamine can be synthesized by combining of methanol and ammonia, prompting their reaction by employing a catalyst. Trimethylamine is sometimes used in the production of industrial chemicals, for the creation of herbicides or plant growth regulators, dyes, choline, and tetramethylammonium hydroxide. There is a genetic disorder that involves an overabundance of trimethylamine in the body, as it fails to be degraded properly. Individuals with this condition often have a strong fish-like odor in their urine or sweat, particularly after the consumption of foods rich in choline. A version of this disorder has also reportedly been observed in chickens.

Biogenic Amines

Biogenic amines are different nitrogenous compounds created by the amination/transamination of ketones or aldehydes, or through the decarboxylation of amino acids. They have low molecular weight and are created by the metabolisms of animals, microbes, and vegetables. The enzymes of raw materials frequently form biogenic amines in beverages or foods. Biogenic amines often play the role of neurotransmitters in the brain, with some examples being histamines, serotonin, epinephrine, norepinephrine, and dopamine.

Histamines mediate attention and arousal in the brain, while serotonin is involved in the regulation of appetite, mood, sexuality, and sleep. Epinephrine is found at the lower levels of the brain, where it functions as a stress hormone. Norepinephrine is also a stress hormone, and it is released by the adrenal glands, playing a role in the regulation of attention, wakefulness, sleep, and feeding cycles. Dopamine plays a role in the motivation/reward cycle, the coordination of movement, and behavioral reinforcement.

Biogenic amines are present in all foods that contain free amino acids or proteins, and as such, they can be found in many different food products like nuts, vegetables, dairy products, fish, and beer. Because many microorganisms can produce biogenic amines, fermented foods are likely to contain high levels of biogenic amines.

Amino Acids

A chart of 21 amino acids commonly used by eukaryotes. Photo: By Dancojocari – Own workPrint It HereThis W3C-unspecified vector image was created with Adobe Illustrator.iThe source code of this SVG is valid., CC BY-SA 3.0,

Amino acids are considered the base units, or building blocks, of proteins and polypeptides. Nitrogen, hydrogen, carbon, and oxygen, or common to all amino acids, though many amino acids have different elements within their side chains. Amino acids typically function as monomers (smaller, simpler molecules that link together to form larger molecules), and when amino acids are joined together they create peptides. Peptides are links together to create a chain of amino acids dubbed polypeptides, and these polypeptides can be transformed into proteins.

The process that creates proteins is called translation, and it is carried out by the ribosomes within a cell. 22 different amino acids are used to create the proteins that are cells need. The amino acids used to create proteins are called proteinogenic amino acids, however not all amino acids can be found in proteins. The neurotransmitter gamma-aminobutyric acid is an example of an amino acid that cannot be found in a protein.