Common Functional Groups in Organic Chemistry

Saturated hydrocarbon chains (such as simple alkanes) are relatively unreactive.

The reactions and reactivity of organic compounds are often determined by the functional groups attached to the carbon chain of which they are a part. It is therefore necessary to be able to recognise and remember information about the most common and important functional groups in order to understand and succeed at organic chemistry.

For each of the functional groups listed below a single example is shown on the right. The examples are all of molecules with carbon chains of 3 carbon atoms, hence the names include "prop" as part of the name, e.g. propane, propene, etc.. Where available links to pages of more examples of chemicals of the same type are included.

About the Structures shown above:

The chemical structures shown in the right-hand column above have been drawn out in full. That is, every chemical bond is represented by a line (or lines, in the cases of double and triple bonds). Many chemistry textbooks, websites and other sources show simpler representations of large or complex molecules in order to save space and / or for clarity. The purpose of the detailed representation here is to show how easy it is to check that you are drawing the correct structure(s) by counting the lines (bonds) extending away from each type of atom.

Students of this level of organic chemistry know that when forming these organic molecules:

  • Hydrogen (H) atoms form one single bond to another element. It must be to another element (and not to another hydrogen atom) because two hydrogen atoms linked together form a single molecule of hydrogen gas, H2.
  • Halogen atoms, that is atoms of fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and, in theory, Astatine (At) also form only one single bond to another element. As for hydrogen, the bond must be to an atom of another element (and not to another atom of the same element) because two halogen atoms linked together form a single molecule of the gas of that element, e.g. F2, Cl2, Br2.
  • Oxygen (O) atoms form either two single bonds to other atoms OR one double bond. Oxygen atoms can form single or double bonds with other oxygen atoms but two oxygen atoms linked together by a double bond form a molecule of oxygen gas (O2), so when working-out or checking drawings of molecular structures in organic chemistry it is worth remembering that a double bond from an oxygen atom does not go to another oxygen atom, but usually to an atom of carbon.
  • Nitrogen (N) atoms form either three single bonds to other atoms (e.g. to two atoms of hydrogen and one of carbon in the case of amines) OR one single bond to another atom and one double bond to a different atom OR one triple bond to another atom. Similar to the cases for the elements mentioned above, when working-out or checking drawings of molecular structures in organic chemistry it is worth remembering that a triple bond from a nitrogen atom does not go to another nitrogen atom because two nitrogen atoms linked together by a triple bond form a singe molecule of nitrogen gas (N2). Triple bonds from nitrogen atoms in organic compounds are generally to carbon atoms (as in nitriles).
  • Carbon (C) atoms form four single bonds to other atoms OR any combination of single, double, or triple bonds that can be represented by a total of 4 lines, where double bonds are represented by two lines between the same two atoms and triple bonds are represented by three lines between the same two atoms.

Therefore when double bonds are represented by two parallel lines and triple bonds are represented by three parallel lines it is easy to check if molecular structures are at least possible by counting the total number of straight lines extending from each atom. However, although this is a useful way to identify any wrong (impossible!) molecular structures, this check alone is not sufficient to guarantee that a structure is drawn correctly. This is due to the existence of multiple isomers of some combinations of elements. For example, see the structures of propanal and propanone (above). They are isomers of each other.

When studying the structures and naming of organic molecules it is useful to see and compare many examples of similar chemicals and their structures. Review the table above then visit the links to further examples in the first column (left-side) of the table.

The above table of organic chemistry functional groups is not a complete list but includes those functional groups required by most UK A-Level Chemistry (that is, AS Chemistry and A2 Chemistry combined) exam boards. Some of this information is also useful for students of GCSE Chemistry.

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