When a solution of a porphin inn-octane is slowly frozen the guests predominantly occupy a single site (A) in which the porphin has been shown to replace a number of host molecules displaced along theb-direction; if the solution is quickly frozen the optical spectra reveal the presence of a second site (B). In the present paper it is shown that the occurrence of these two types of sites,AandB, is a common phenomenon throughout the series fromn-heptane (C7) ton-decane (C10) as hosts and phenomenological criteria are formulated to distinguish between the two kinds of sites.