A Proposal for Rule 6: Spiro and other axially-symmetric compounds. Early on in the development of the CIP system, it was recognized that certain cases involving C2, D2, and C3 point groups require additional consideration for assignment of stereodescriptors; an S4 case was described later 3 (Figure ). Specifically, an algorithm must distinguish between both enantiomers of compounds VS285, VS281, and VS283, and yet still deliver no stereodescriptors for cubane (VS009) and the S4 compound VS012. Only simple spiro structure VS285 is mentioned in BB 2013, in section P-93.5.3.