Can I compare structures by looking at specific layers from their InChIs?
Taken from the InChI Technical Manual. “Values computed for each layer depend on prior layers. As a consequence, for example, two stereochemical layers for different compounds cannot be directly compared – comparisons must involve the complete set of preceding layers. Layers do not, however, depend on successive layers.” The above image highlights why you cannot directly compare layers such as the stereochemical layer without taking earlier layers into account. The two compounds are clearly different (and thus have different main layers), yet both have the same stereochemical layer. This is because the stereochemical layer only holds the canonical number for a stereocentre and its stereochemistry, with all the information from the earlier layers used in calculating the stereochemistry being absent. Therefore, directly comparing the stereochemical layers of the two compounds would be analogous to stating “these two compounds are identical, as each has a stereocentre at atom no. 2 with s
