# Why do highly branched alkanes have higher octane numbers than their corresponding linear isomer?

The octane number of fuels are based on a set of primary reference fuels, which are mixtures of iso-octane and n-heptane. Now iso-octane being branched alkane has very less tendency to react and given ON=100 and n-heptane reacts easily and given ON=0. However n-octane that is the corresponding linear isomer of iso-octane has an ON<0. Now why does branching in a alkanes reduce its reactivity?