just try to analyse the stability of the compound since every substance in this universe try to be in most stable possible for it    for eg  n hexane   does not react with licl since assume that when licl react with benzene and form 1 chloro hexane and lih is formed but lih is not  as stable as the licl hence licl doesnt loose the chlorine to get replaced by the hydride    remember u must also see the stability of the n hexane  and 1 chloro hexane