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?
$\begingroup$
$\endgroup$
0
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
5
The current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) reads as follows:
P-14.4 NUMBERING
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.
Furthermore,
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’.
-
$\begingroup$ I see that the locant set of 1,2,4 is lower than 1,3,4 but the precedence of ethyl is greater than fluorine .. so shouldn't ethyl get the lowest number ? $\endgroup$ Feb 7, 2015 at 15:19
-
2$\begingroup$ @user126190 The prefixes (‘ethyl’, ‘fluoro’, and ‘nitro’) are ‘all considered together in a series of increasing numerical order’. $\endgroup$– user7951Feb 7, 2015 at 15:36
-
$\begingroup$ But this website link and many other websites too say alkanes are before halogens .. $\endgroup$ Feb 8, 2015 at 11:33
-
1$\begingroup$ @user126190 Your link is about the seniority of functional classes in functional class nomenclature, which is not related to your question. In your example, the functional class is already given; it is neither alkane nor alkyl halide – it is benzene. $\endgroup$– user7951Mar 28, 2015 at 17:21
-
$\begingroup$ @Loong is correct. As far as numbering of locants is concerned, alkyls, alkoxys, halos, and nitros all has the lowest priority because they are substituent only functional groups. $\endgroup$ Jun 1, 2015 at 18:38