This question is a follow-up to a recent question on discodermolide stereochemistry that I answered here. In the course of reading IUPAC's definition of "stereogenic center", I wondered if axially chiral molecules such as BINOL have a "stereogenic unit" according to IUPAC.
The part of IUPAC's definition that may (or may not) apply to BINOL is:
A chain of four non-coplanar atoms (or rigid groups) in a stable conformation, such that an imaginary or real (restricted) rotation (with a change of sign of the torsion angle) about the central bond leads to a stereoisomer.
Here is the structure of (S)-BINOL:
Does the four-atom chain consisting of the O-bond carbons plus the transannular C-C-bound carbons qualify? I can't quite work out what is meant by "with a change of sign of the torsion angle" and "stable conformation". If it does qualify, suppose temperature is increased to the point where spontaneous racemization happens (and suppose that any side reactions or decomposition can be ignored). Is that chain no longer a stereogenic unit?