One of the most important issues in chemoinformatics is how to compare molecules. There are two equally important aspects to this issue: (1) how to represent the information in a molecular structure in a computationally appropriate form and (2) how to determine the structural relationship of one molecule to another using this information. In the first instance, a common approach in widespread use today is the development of 'vectorized' representations of molecular structure such as that exemplified by Extended Connectivity Fingerprints (ECFP) . Other related approaches such as MACCS key fingerprints represent the structural features of molecules as binary vectors whose components are based on the presence or absence of specific substructural features. Many of these and closely related methods provide a basis for developing all manner of AI models. An important caveat regarding these approaches is that they deal almost exclusively with 2D molecular structures. Three-dimensional structural features, such as multiple conformations, are rarely treated for a variety of reasons.