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Cl-, CH3- and NO2-substituted benzene derivative

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.

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    $\begingroup$ "as halogens have higher priority than a nitro-group" there is your mistake (or the mistake of your teacher). $\endgroup$
    – Loong
    Feb 9, 2021 at 11:38
  • $\begingroup$ @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. $\endgroup$ Feb 9, 2021 at 11:53
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    $\begingroup$ Your teacher is also talking about "the lowest sum"? That's his second mistake. $\endgroup$
    – Loong
    Feb 9, 2021 at 12:01
  • $\begingroup$ @Loong I mean he is talking about the lowest locant rule $\endgroup$ Feb 9, 2021 at 12:03
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    $\begingroup$ 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. $\endgroup$
    – Loong
    Feb 9, 2021 at 12:10

1 Answer 1

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The main goal of IUPAC names is to keep them simple and understandable by anyone. So, you basically want to keep numbers the lowest possible. Hence, you shall start numbering where it will give the lowest numbers for your substituents.

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.

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    $\begingroup$ Please see How to ask and answer nomenclature questions? $\endgroup$
    – andselisk
    Feb 9, 2021 at 9:52
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    $\begingroup$ My teacher says the same thing, that before considering the lowest sum, we give the main functional group the number 1 $\endgroup$ Feb 9, 2021 at 11:55
  • $\begingroup$ I meant the lowest locant rule $\endgroup$ Feb 9, 2021 at 12:04
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    $\begingroup$ @AkshatVats There is no "main functional group" in this compound. All three substituent groups are considered together. $\endgroup$
    – Loong
    Feb 9, 2021 at 12:11
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    $\begingroup$ @AkshatVats I already did. You can find it if you follow the duplicate link at your question. My answer is here: chemistry.stackexchange.com/a/53566/101286 $\endgroup$
    – Loong
    Feb 9, 2021 at 15:26

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