“…It was pointed out long ago (7) that olefin hydrocarbons differ from the paraffins in their tendency to knock. Data have been published (1,2,8) on the knock characteristics of several isolated aliphatic olefins of definite structure-namely, 2-pentene, trimethylethylene, and diisobutylene-and as might be expected from analogy with the paraffin hydrocarbons, there appears considerable difference between the two isomeric pentenes upon which data are available.…”