Isooctane, octane rating scale

The burning properties of hydrocarbons depend on their structure. Isooctane (2,2,4-trimethylpentane) is the standard used to assign octane ratings. The octane rating is an arbitrary scale for rating the relative knocking prop-... 

Gasolines are usually rated according to the octane number, a measure of their tendency to cause knocking. On this scale, a branched Cg compound (2,2,4-trimethylpentane, or isooctane) has been arbitrarily assigned an octane number of 100, and that of n-heptane, a straight-chain compound, is zero. The higher the octane number of the hydrocarbon, the bet-... 

The best isomer— trimethylbutane (called triptane)— proved to be too difficult to make in the large quantities required for testing, though it is superior to isooctane. The octane was selected as the rating of 100 on the octane scale. The compound n-heptane was selected as the 0 rating. 

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