What is the meaning of n in n-octane and similar compounds?
In this case, n means "normal", i.e. straight chain. This is somewhat of a holdover from the olden days, but in the case of octane in particular, it makes sense to specify n-octane if that is what you have. For example, the "octane" used as a standard gasoline engine fuel against which gasolines are rated (by definition, 100 octane) is actually not n-octane, but rather 2,2,4-trimethylpentane - a branched isomer of octane - in contrast to the straight chain version.