Melting points (in blue) and boiling points (in pink) of the first fourteen alkanes (temperatures in degrees Celsius, number of carbon atoms along the horizontal axis).

In addition to reactivity, the physical properties of an organic substance, such as melting point, boiling point and solubility, are amont its most important traits. The physical properties of an organic substance can often be predicted from its structure. In most cases, a substance's molecular weight and the functional groups are sufficient information to allow for a good estimate of the melting point, boiling point, and solubility to be estimated. Comparing molecules of similar size, the greater the strength of intermolecular force, the more equilibrium will favor the condensed phase at a given pressure and temperature.

Understanding how functional groups affect the physical properties of organic compounds is of primary importance to laboratory organic chemistry, and, furthermore, one of the bridges from organic chemistry to biochemistry and cell biology. The student must obtain this form of understanding to be able to grasp protein folding, for example, or the structure of biological membranes. Every MCAT makes this area a priority. You can expect both direct and indirect questions. Straightforward questions asking for a comparison of solubilities are common, for example, as are questions involving similar reasoning in a more advanced biological context.