Formal nomenclature for fulvene

I am a little bit confused trying to name the compound fulvene:


[![fulvene](https://i.stack.imgur.com/cHvVx.png)](https://i.stack.imgur.com/cHvVx.png)


I'm not sure whether its name is 5-methylene-1,3-cyclopentadiene or 3-methylene-1,4-cyclopentadiene.




Fulvene consists of a cyclopentadiene ring and a $\ce{{}=CH2}$ substituent group. According to the current version of *[Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book)](http://dx.doi.org/10.1039/9781849733069-fp001),* the prefix ‘methylene’ is no longer recommended to designate the $\ce{{}=CH2}$ group. The preferred prefix is ‘methylidene’; thus, the systematic name of fulvene without locants is methylidenecyclopentadiene.


Concerning the numbering of locants, the current IUPAC recommendations read 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:
> 
> 
> (…)
> 
> 
> (e) saturation/unsaturation:
> 
> 
>   (i) low locants are given to hydro/dehydro prefixes (…) and ‘ene’ and ‘yne’ endings;
> 
> 
>   (ii) low locants are given first to multiple bonds as a set and then to double bonds (…);
> 
> 
> (f) detachable alphabetized prefixes, all considered together in a series of increasing numerical order;
> 
> 
> (…)
> 
> 
> 


Therefore, low locants are given first to the double bonds in the ring according to (e) and then to the prefix ‘methylidene’ according to (f). Thus, the correct systematic name is **5-methylidenecyclopenta-1,3-diene** rather than 3-methylidenecyclopenta-1,4-diene since the locant set ‘1,3’ for the double bonds is lower than ‘1,4’.


![35-methylidenecyclopenta-1,3-diene](https://i.stack.imgur.com/bYJGu.png)
Note that according to IUPAC nomenclature since 1993, locants are placed immediately before that part of the name to which they relate (e.g. cyclopenta-1,3-diene rather than 1,3-cyclopentadiene).


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