When the rings of a steroid are represented as projections onto a plane in the conventional manner, an atom or group is called if it projects below the plane and if it projects above the plane.
This '/-system' has been extended to other cyclic natural products and related products (see, for instance, Section E, Stereochemistry and Stereoparents, pp. 192I-212I, in 'Chemical Substance Index
Names', Appendix IV, in the 1992 Index Guide, Chemical Abstracts Services, Columbus, Ohio 1992).
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(Recommendations 1993), 1993, Blackwell Scientific publications, Copyright 1993 IUPAC]. If you need to cite these rules please quote this reference as their source.
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