Definition of Locant

The term locant is used in organic chemistry to name and classify the organic molecules. It is defined as a number or a figure that is used in indicating and representing the position of a functional group that is being present in the organic molecule. Take an example of pentanone which has ketone as its functional group. It has 5 carbons in the chain and two isomers i.e. 2-pentanone and 3-pentanone.


The carbon atoms in the chain are numbered from 1 to 5 starting from one end and continuing along the chain. The locant is the number of the carbon atom to which the atom of oxygen is being bonded. If the oxygen atom is bonded to the third carbon, then the locant is said to be three but if the oxygen atom is bonded to any other carbon say second or fourth, then the locant is 2 and 4 respectively. The locant is added to the name of the molecule to avoid any kind of ambiguity.

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