I think that toluene is a common name for 1-methylbenzene. And in IUPAC nomenclature, we must provide formal prefixes and suffixes along with correct numbering so the only correct option must be 1-chloro-4 methylbenzene.


1 Answer 1


The use of 'toluene' as a parent hydrocarbon in nomenclature is described in Rule P-22.1.3 in Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013.

These names [toluene, xylene, and mesitylene] are retained due to a long and well established tradition. Toluene and xylene are preferred IUPAC names, but are not freely substitutable; toluene is substitutable under certain conditions, but only for general nomenclature. (emphasis mine)

"General nomenclature" refers to any name generated by the use of IUPAC principles, rules, and conventions, whereas the "preferred IUPAC name" (PIN) refers to a name that is preferred among two or more names generated from two or more IUPAC recommendations. The introduction P-10 reads:

Any name other than a preferred IUPAC name, as long as it is unambiguous and follows the principles of the IUPAC recommendations herein, is acceptable as a 'general IUPAC name", in the context of a 'general IUPAC nomenclature'.

As stated in P-22.1.3, in the construction of a PIN for the molecule below, the use of 'toluene' as the parent hydrocarbon is not permitted; the PIN is 1-chloro-4-methylbenzene.


Regarding the substitution of toluene in general nomenclature, P- lists the characteristic groups that can be used in general nomenclature:

[...] halides $\ce{-Br, -Cl, -F, -I}$, pseudohalides $\ce{-N3, -NCO}$ (and chalcogen analogues), $\ce{-NC}$, substituent groups derived from the halogen oxo acids $\ce{-ClO, -ClO2, -ClO3}$ (similarly for groups in which $\ce{Cl}$ is replaced by $\ce{Br}$ or $\ce{I}$), $\ce{-NO2}$ and $\ce{-NO}$, and $\ce{-OR}$ ($\ce{R}$ = alkyl groups), and chalcogen analogues, and $\ce{-SO-R}$ and $\ce{-SO2-R}$, and $\ce{Se}$ and $\ce{Te}$ analogues.

Since chloride falls under this list, the name 4-chlorotoluene is permissible in general nomenclature, but it is not the preferred IUPAC name.

Note that there is no space between the prefix 'chloro' and the parent hydride name 'toluene'.

Also note that there is no such thing as '1-toluene'; in the name '4-chlorotoluene', for example, the methyl group of toluene is automatically assigned the locant '1' (see figure below from the Recommendations). Therefore, the name '4-chloro-1-toluene' is incorrect.

Locant numbering in toluene

  • $\begingroup$ The question says "the iupac name(s) of the compound is/are" so does it refer to pin or general name $\endgroup$ Jun 5, 2017 at 6:24
  • 5
    $\begingroup$ Sorry but I can't interpret ambiguous wording for you. $\endgroup$
    – orthocresol
    Jun 5, 2017 at 6:28

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