Naming double bond sidechain [duplicate]








**This question already has answers here**:
 
 




[How do you name an alkene using IUPAC rules if the longest carbon chain in this alkene does not include the double bond?](/questions/28554/how-do-you-name-an-alkene-using-iupac-rules-if-the-longest-carbon-chain-in-this)

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Closed 8 years ago.



![enter image description here](https://i.stack.imgur.com/foH3j.png)


In IUPAC naming double bonds take preference over an alkane chain of any length, right? So the above should be named as `2-ethylnon-1-ene`.


However, when I verify with chemdraw it gives the answer as `3-methylenedecane`. I cannot seem to find any mention of double bond side chains as `alkylene` anywhere on the internet... Is this common nomenclature, and if not why would chemdraw name it as this? 




According to IUPAC rules first thing you need to see is **longest carbon chain** which is 10(deca) over here.


Then while **numbering the Carbon** double bond is given preference.


So above compound is 10 carbon chain in which 3rd carbon is double bonded.


Thus, **3-methylenedecane** is correct name. 




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Few more such examples to make it more clear:


1. **2,6,10-trimethyldodec-1-ene**


![enter image description here](https://i.stack.imgur.com/h9UTt.png)


2. **8-ethyldec-1-ene**


![enter image description here](https://i.stack.imgur.com/jJJ7t.png)


Example Source: [ChemSink](http://www.chemsink.com/index.py?q=CCCCCCCC%28%3DC%29CC)




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**Basic IUPAC rules:**


1. Find the longest chain in the molecule and name it.
2. Name all groups attached to the chain as alkyl substituents.
3. Number the carbons of the longest chain beginning with the end that is closest to a substituent.
4. Write the name of the alkane by first arranging all of the substituents in numerical order (each preceded by the number of the carbon to which it is attached and a hyphen), and then add the name of the stem.
Haloalkanes.
5. The halogen is treated as an alkyl substituent, without any priority.
6. Ethers are named as alkoxyalkanes. The first carbon of the alkoxy substituent is numbered as C-1 of that substituent.


**Note that these rules are changed as of 2008. Older HW and exams have slightly different answers.**


Rules Source: <http://valhalla.chem.udel.edu/nomenclature.html>


 1

It looks like you're correct.


This molecule has been given 2-ethyl-1-hexene or [2-ethylhex-1-ene](http://chemwiki.ucdavis.edu/Organic_Chemistry/Hydrocarbons/Alkenes/Naming_the_Alkenes)
![enter image description here](https://i.stack.imgur.com/urxn0.gif) 


Another name for your molecule would be 3-methylidenedecane. 


Added from [Wikipedia](http://en.wikipedia.org/wiki/Methylene_(compound)): 


The trivial name carbene is the preferred IUPAC name. 


The systematic names methylidene and dihydridocarbon are constructed according to the substitutive and additive nomenclatures, respectively.


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