How do we assess the purity of organic compounds?
Undoubtedly, the most convenient means to assess purity is a comparison between the experimental melting point and the literature melting point. Melting points provide a very convenient means to identify organic compounds, and to assess their purity.
When a new organic compound is synthesized, it is usually recrystallized to constant melting point, and this measurement provides the basis for future comparison. When you identify organic unknowns on the basis of the melting points of their derivatives, the challenge is to get your derivative sufficiently pure and dry to give a melting point consistent with the literature data.