Why is 4-ethyl-1-fluoro-2-nitrobenzene (structure is in the attached picture) called so ?
Shouldn't it be called as 1-ethyl-4-fluoro-3-nitrobenzene since the precedence of ethyl is greater than halogens?
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The current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) reads as follows:
When several structural features appear in cyclic and acyclic compounds, low locants are assigned to them in the following decreasing order of seniority:
(f) detachable alphabetized prefixes, all considered together in a series of increasing numerical order;
(g) lowest locants for the substituent cited first as a prefix in the name;
Note that Rule f takes precedence over Rule g. Also note that all prefixes (i.e. ethyl, fluoro, and nitro) are considered together; i.e., there isn’t any order of functional group priorities at this point.
P-14.3.5 Lowest set of locants
The lowest set of locants is defined as the set that, when compared term by term with other locant sets, each cited in order of increasing value, has the lowest term at the first point of difference; (…)
Therefore, the example is named as 4-ethyl-1-fluoro-2-nitrobenzene rather than 1-ethyl-4-fluoro-3-nitrobenzene since the locant set ‘1,2,4’ is lower than ‘1,3,4’.