Heptanes and Higher Alkanes

V. Isomerization of Heptanes and Higher Alkanes 1. Without Cracking Suppressors... 

The foregoing study indicates that, unlike n-pentane and hexanes, hydrogen does not suppress the formation of side reactions during the action of aluminum chloride on n-heptane and higher alkanes. 

Light alkanes do not undergo exothermic proton transfer reactions with H3O. However, as the molecular mass increases, the proton affinity of the alkane increases and therefore for larger alkanes the proton transfer process eventually becomes exothermic. Arnold and coworkers have estimated that the endothermic/exothermic crossover point occurs at hexane, such that all heavier alkanes should have clear exothermic proton transfer reactions with H3O+ [10]. For heptane and higher alkanes, fast reaction with H3O+ is seen but the rate coefficient falls short of that predicted from the collision-limiting models presented in Section 2.23.2. Furthermore, reaction is dominated not by proton transfer but instead by association, that is... 

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