Not all tetracoordinate atoms will be stereocenters. A stereocenter is an atom whose "ligand permutation produces stereoisomers," as defined by Mislow and Siegel . The presence of four bonds around a central atom is therefore a necessary, but insufficient condition to form a stereocenter. Molecular topology can result in permutation that does not yield stereoisomers. The assignment of non-default parities to such atoms should therefore be avoided.