Naming compounds

When naming compounds, where are you meant to put the number of the functional group?
Because some of the compound names I have seen have them at the start and others in the middle? Is there a reason for this?

Kia ora!

The number is put immediately before the part of the name to which they relate – such as the functional group

e.g., hex-2-ene has an alkene functional group, and the double bond starts on the second carbon (is between the second and third carbons).

Note: before 1993 (when the IUPAC rules were changed) the naming would have been 2-hexene – but this naming is now obsolete.

If the compound had a methyl group attached, then the number showing where the methyl group is attached would be in front of methyl

e.g., 3-methylhex-2-ene


The double bond is between the second and third carbons so the number 2 is placed before the “ene”; the compound also has a methyl side chain attached to the third carbon atom so the number 3 is placed before the “methyl”.

Good luck!

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