Characterization of chemical structures

It is fundamental to the development of any quantitative structure-activity relationship (QSAR) that the structures of the compounds be fully and accurately represented. It is most usual for the compounds in the chosen data set to be modeled on computers for which a range of molecular modeling and computational chemistry software is available. In order for this highly labor-intensive facet of a QSAR study to be successful, it clearly must result in a set of accurate chemical structures. The subsequent calculation of a range of molecular descriptors on which the QSAR will depend ideally will only be valid if the chemical structures are as close as possible to their actual characteristics in the aqueous phase and at ambient temperatures and pressures. Although it is not possible unambiguously to determine this by experiment, a combination of data from X-ray crystallography, NMR, and other spectroscopic techniques can give good clues to the structural features of chemicals, with which to validate computer molecular models.