# How do I call the functional group of this alkane?

Given the following chain of carbon atoms (imagine they are all saturated with the correct number of hydrogen atoms), how do I call it? 4-(dimethyl-ethyl)-octane? I'm having trouble naming the short carbon chain extending from the 4th carbon atom of the octane. Can you help me out please?

Under the 2004 provisional recommendations by IUPAC, one possible systematic name is 4-(2-methylpropan-2-yl)octane, which indicates that the longest chain in the substituent is three carbons long, is connected to the main carbon chain via the second carbon (-2-yl), and has a methyl group on the second carbon (2-methyl).

4-(1,1-dimethylethyl)octane is also possible, and indicates that there is an ethyl substituent on the fourth carbon in octane, which is further substituted with two methyl groups on the first carbon where it branches off (see section P-29.4).

However, the preferred IUPAC name is 4-tert-butyloctane; the tert-butyl group is used to describe a $\ce{-C(CH3)3}$ group and is preferred over either of the two above systematic names (see section P-56.2.2.2).

I don't have access to the 2013 recommendations but I believe it should not be different.

• In the 2013 edition, the structure and wording of several rules have changed, which makes them difficult to compare to the 2004 draft. Anyway, the resulting names and the preference for “4-tert-butyloctane” has not changed. However, note that the current IUPAC recommendations do not use parentheses in “4-tert-butyloctane”. – Loong Nov 14 '15 at 14:54
• @Loong Okay, edited. – orthocresol Nov 14 '15 at 15:14

4-tert-butyloctane is allowed according to IUPAC

• Could you elaborate a bit? This isn't really helpful to the OP nor to anyone else visiting this post. Is 4-t-butyl octane the preferred IUPAC name? How did you name the compound like that? And so on, are questions you can answer in order to write a decent post. – M.A.R. Nov 14 '15 at 13:11

2,2-dimethyl-3-propylheptane

Choose the 7 carbon chain instead. Not necessary to be the longest chain in this case

• Yes it is. Choosing the longest all-carbon chain is always necessary for saturated alkanes. – Jan Nov 14 '15 at 14:50