# Numbering for the IUPAC name of this benzene derivative [duplicate]

My first guess was 2-chloro-4-nitrotoluene, but this was not among the choices for this question. My teacher says we will begin numbering from Cl, as halogens have higher priority than a nitro-group. However, this compound is named 2-chloro-1-methyl-4-nitrobenzene on PubChem.

I am confused. Please explain where should I begin numbering from.

• "as halogens have higher priority than a nitro-group" there is your mistake (or the mistake of your teacher). – Loong Feb 9 at 11:38
• @Loong And what do I tell him so he understands? He says the same thing, that before considering the lowest sum, we give the main functional group the number 1. – Akshat Vats Feb 9 at 11:53
• Your teacher is also talking about "the lowest sum"? That's his second mistake. – Loong Feb 9 at 12:01
• @Loong I mean he is talking about the lowest locant rule – Akshat Vats Feb 9 at 12:03
• Neither "chloro" nor "nitro" nor "methyl" can be the principal characteristic group (which would be expressed as a suffix or implied by a traditional name); there are no priorities for these three groups. So there is no principal characteristic group in this compound that would automatically get the lowest locant. – Loong Feb 9 at 12:10

For instance, if you began numbering from the carbon bonded with the chlorine, your molecule would have been named 1-chloro-2-methyl-5-nitrobenzene or 1-chloro-6-methyl-3-nitrobenzene. Or, if you chose your numbering to begin from the other group, you'd have named it 3-chloro-4-methyl-1-nitrobenzene or, even worse, 5-chloro-4-methyl-1-nitrobenzene. With these examples, you can notice that the simplest name, i.e. the one that has the lowest numbers, is the one PubChem gave you : and that's the reason one should start numbering by the methyl.