I want to identify the correct IUPAC name for this compound:

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I would say this is 2-methyl-5-(methylethyl)-5-(1-methylpropyl)-nonane. However, the solution manual says that it is 2-methyl-5-(1-methylethyl)-5-(1-methylpropyl)-nonane.

I don't understand why the first "1-" index is necessary. It doesn't add any information, as "(2-methylethyl)" would actually be just a propyl.

Am I missing something?

  • $\begingroup$ Awesome question. Possible reference: acdlabs.com/iupac/nomenclature, iupac blue book online (although they don't have the 2013 version). $\endgroup$ – JSCoder says Reinstate Monica Mar 19 '18 at 22:10
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    $\begingroup$ The suggested name “2-methyl-5-(1-methylethyl)-5-(1-methylpropyl)-nonane” seems to be based on obsolete IUPAC recommendations from 1979. The preferred name according to current (2013) IUPAC nomenclature is 5-(butan-2-yl)-2-methyl-5-(propan-2-yl)nonane and many people would probably still call it 5-(sec-butyl)-5-isopropyl-2-methylnonane. $\endgroup$ – user7951 Mar 31 '18 at 8:45
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    $\begingroup$ Related: IUPAC rules on omission of locants in carboxylic acid $\endgroup$ – user7951 Mar 31 '18 at 8:47

I'd not subtract a point for your "mistake," because there is no point to prove you are wrong. However, suppose the group is different than methyl. Then the position matter at that point. Say its bromo-group. So, 1-bromoethyl- and 2-bromoethyl- are two different things. That's why that rule is for. Can't give any favors just for methyl! :-)

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