Why may a stereo layer appear several times in a single InChI?
As additional levels are added, stereodescriptors may change, and this may result in a new stereo layer. An example is shown below. We see that in the Stereo Layer, as no isotopes are taken into consideration, only the chiral center at 3 is calculated as H and D are seen as equivalent. In the Isotopic Layer the H and D are seen as different and so an Isotopic Stereo sub-layer is included with stereo information for chiral centres 2 and 3.
