MM3 is a widely used molecular mechanics computer program used to calculate the three dimensional structure of molecules. It has been parameterized for several individual classes of functional groups. This paper examines the accuracy of MM3 in calculating the structure of compounds that contain multiple functional groups. The calculated values from MM3 will be compared to data from x-ray diffraction, a commonly used method of determining molecular structure. The number and type of missing parameters will be examined. The accuracy of MM3s calculated values will be compared to the values measured by x-ray diffraction.|Based on the results of this study MM3 is fairly accurate at calculating complex molecular structure. Certain properties specific to the solid state such as molecular vibration and intermolecular forces must be accounted for in order to improve the accuracy of MM3 in calculating solid phase structure.