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I was presented with the following question in an online test:
To avoid any confusion, here are the arranged options:
A. 2-Chlorotoluene
B. 1-Chloro-2-methylbenzene
C. B and D
D. O-ChlorotolueneCorrect answer: (C) B and D.
Explanation: Chloro is given priority so numbered as 1
My question is: Are the ortho, meta and para prefixes part of the official IUPAC nomenclature or not?
I chose B, what should be the correct answer to this question?
According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book),
The locants o, m, p are no longer recommended; the numerical locants '1,2-', '1,3-', and '1,4-' must be used in substitutive names. However, as an exception, the three isomers of xylene are still recognized as o-, m-, and p-xylene in general IUPAC nomenclature (see P-22.1.3).
and
The letters o, m, and p have been used in place of ortho, meta, and para, respectively, to designate the 1,2-, 1,3-, and 1,4- isomers of disubstituted benzene. This usage is strongly discouraged and is not used in preferred IUPAC names.
The preferred IUPAC name for the compound that is given in the question is 1-chloro-2-methylbenzene.
The name 2-chlorotoluene may be used in general nomenclature.
