Common Functional Groups in Organic Chemistry

Organic Chemistry Functional Groups Structures and Characteristics

Functional groups determine the reactions and properties of organic compounds.
Functional groups determine the reactions and properties of organic compounds. MOLEKUUL/SCIENCE PHOTO LIBRARY / Getty Images

Functional groups are collections of atoms in organic chemistry molecules that contribute to the chemical characteristics of the molecule and participate in predictable reactions. These groups of atoms contain oxygen or nitrogen or sometimes sulfur attached to a hydrocarbon skeleton. Organic chemists can tell a lot about a molecule by the functional groups that make up a molecule. Any serious student should memorize as many as they can. This short list contains many of the most common organic functional groups.

It should be noted that the R in each structure is a wildcard notation for the rest of the molecule's atoms.

Key Takeaways: Functional Groups

  • In organic chemistry, a functional group is a set of atoms within molecules that function together to react in predictable ways.
  • Functional groups undergo the same chemical reactions no matter how large or small the molecule is.
  • Covalent bonds link the atoms within functional groups and connect them to the rest of the molecule.
  • Examples of functional groups include the hydroxyl group, ketone group, amine group, and ether group.

Hydroxyl Functional Group

Hydroxy functional group
This is the general structure of a hydroxyl functional group.

Itineranttrader / public domain

Also known as the alcohol group or hydroxy group, the hydroxyl group is an oxygen atom bonded to a hydrogen atom. Hydroxy groups link biological molecules together via dehydration reactions.

Hydroxyls are often written as OH on structures and chemical formulas. While hydroxyl groups are not highly reactive, they do readily form hydrogen bonds and tend to make molecules that contain them soluble in water. Examples of common compounds containing hydroxyl groups are alcohols and carboxylic acids.

Aldehyde Functional Group

This is the general structure of the aldehyde functional group.
This is the general structure of the aldehyde functional group. Todd Helmenstine

Aldehydes are made up of carbon and oxygen double-bonded together and hydrogen bonded to the carbon. An aldehyde may exist as either the keto or enol tautomer. The aldehyde group is polar.

Aldehydes have formula R-CHO.

Ketone Functional Group

This is the general structure of the ketone functional group.
This is the general structure of the ketone functional group. Todd Helmenstine

A ketone is a carbon atom double bonded to an oxygen atom that appears as a bridge between two other parts of a molecule.

Another name for this group is the carbonyl functional group.

Note how the aldehyde is a ketone where one R is the hydrogen atom.

Amine Functional Group

This is the general structure of the amine functional group.
This is the general structure of the amine functional group. Todd Helmenstine

Amine functional groups are derivatives of ammonia (NH3) where one or more of the hydrogen atoms are replaced by an alkyl or aryl functional group.

Amino Functional Group

The beta-Methylamino-L-alanine molecule has the amino functional group.
The beta-Methylamino-L-alanine molecule has the amino functional group. MOLEKUUL/SCIENCE PHOTO LIBRARY / Getty Images

 The amino functional group is a basic or alkaline group. It's commonly seen in amino acids, proteins, and the nitrogenous bases used to build DNA and RNA. The amino group is NH2, but under acidic conditions, it gains a proton and becomes NH3+.

Under neutral conditions (pH = 7), the amino group of an amino acid carries the +1 charge, giving an amino acid a positive charge at the amino portion of the molecule.

Amide Functional Group

This is the general structure of the amide functional group.
This is the general structure of the amide functional group. Todd Helmenstine

Amides are a combination of a carbonyl group and an amine functional group.

Ether Functional Group

This is the general structure of an ether functional group.
This is the general structure of an ether functional group. Todd Helmenstine

An ether group consists of an oxygen atom forming a bridge between two different parts of a molecule.

Ethers have formula ROR.

Ester Functional Group

This is the general structure of an ester functional group.
This is the general structure of an ester functional group. Todd Helmenstine

The ester group is another bridge group consisting of a carbonyl group connected to an ether group.

Esters have formula RCO2R.

Carboxylic Acid Functional Group

This is the general structure of the carboxyl functional group.
This is the general structure of the carboxyl functional group. Todd Helmenstine

Also known as the carboxyl functional group.

The carboxyl group is an ester where one substituent R is a hydrogen atom.

The carboxyl group is usually denoted by -COOH

Thiol Functional Group

This is the general structure of the thiol functional group
This is the general structure of the thiol functional group. Todd Helmenstine

The thiol functional group is similar to the hydroxyl group except the oxygen atom in the hydroxyl group is a sulfur atom in the thiol group.

Thiol functional group is also known as a sulfhydryl functional group.

Thiol functional groups have formula -SH.

Molecules that contain thiol groups are also called mercaptans.

Phenyl Functional Group

This is the general structure of the phenyl functional group.
This is the general structure of the phenyl functional group. Todd Helmenstine

This group is a common ring group. It is a benzene ring where one hydrogen atom is replaced by the R substituent group.

Phenyl groups are often denoted by the abbreviation Ph in structures and formulas.

Phenyl groups have formula C6H5.

Sources

  • Brown, Theodore (2002). Chemistry: The Central Science. Upper Saddle River, NJ: Prentice Hall. p. 1001. ISBN 0130669970.
  • March, Jerry (1985). Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.). New York: Wiley. ISBN 0-471-85472-7.
  • Moss, G. P.; Powell, W.H. (1993). "RC-81.1.1. Monovalent radical centers in saturated acyclic and monocyclic hydrocarbons, and the mononuclear EH4 parent hydrides of the carbon family". IUPAC Recommendations. Department of Chemistry, Queen Mary University of London.

Functional Group Gallery

This list covers several common functional groups, but there are many more because organic chemistry is everywhere. Several more functional group structures can be found in this gallery.