What is the IUPAC name of iso-octane?

I know that the IUPAC name of iso-octane 2,2,4-trimethyl pentane but why is it not 2-methyl heptane. As far as i know, prefix-iso is used for those paraffins in whch a methyl group is attached to the second last carbon atom of the continous chain.
Why isn't this rule applicable here.

1 Answer
Jan 2, 2016

It is used as reference for the octane number, so the reason is historical.


Strictly speaking, you are correct. However, from all the isomers of octane, 2,2,4-trimethyl-pentane is the most important because of it's anti-knocking character in gasoline fuels. Specifically the octane number is defined:

A gasoline fuel with an octane number of 95 has the same antiknocking character as a mixture of 95% v/v of iso-octane (2,2,4-trimethyl-pentane) and 5% v/v n-heptane.