We report a study of the dissolution temperature of n-hexacontane, as a function of concentration, with 52 different solvents, aimed at understanding the effect of molecular flexibility on the entropy-of-mixing. The entropy-of-mixing of rigid molecules may be expected to follow ideal mixing combinatorics and go as ln(mole fraction), while for flexible polymers it is expected to follow Flory-Huggins In(volume fraction). By isolating the entropy-of-mixing, we have experimentally found that rigidity, through ring structures, causes deviations from the Flory-Huggins behavior; and we have proposed a crossover form for the entropy-of-mixing which varies between In(volume fraction) and In(mole fraction) according to molecular rigidity.