Iso-octane has octane number of 100 2, 2, 4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2 . It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scale.