Isooctane

 2,2,4-Trimethylpentane is commonly known as isooctane (the one with one methyl group at the 2 position of the main chain is called "iso", and the one with two methyl groups at the 2 position is called "new". However, To get used to, I still use 2,2,4-trimethylpentane as "iso-octane"), which is an isomer of octane