A locant is a number used to clearly identify the location of a functional group or substituent on the parent carbon chain.
Using the correct locant is a very important part of the IUPAC system of naming organic compounds. A few rules follow –
- When only 1 substituent is present, assign it the lowest possible number.
- For more than 1 substituent, assign the locant such that the 1st substituent receives the lowest number. In case of a tie, the second locant must be the lower number
- When the rule above fails and there is a tie in all cases, assign the locant alphabetically