What percentage ratios relative to each other does the three isomeric alkene hydrocarbons of butylene exist in gasoline? And how much does their presence affect overall octane number if only four carbons instead of six to eight carbons like in most of the rest of the gasoline? Does the presence of the three isomeric forms of butylene reduce overall octane a small amount? Since it's a smaller hydrocarbon,I would guess that it would reduce it some. Shorter chains usually equate into less chemical energy per molecule. It also seems like it would evaporate away faster than the other gasoline hydrocarbons. But the overall percentage of butylenes relative to the rest of the larger hydrocarbons is probably small, I would presume?