Steroid Nomenclature, Numbering, Double Bonds and Stereochemistry

The general formula for the basic structure of the above cited compounds may be represented as follows  

The rings are conventionally lettered and numbered as indicated above. However, in actual conformation the basic structure of steroid is not planar. It has also been observed that in the naturally occurring steroidal compounds the substitutions in the rings usually occm at C-3, C-7 and C-11 positions. 

According to the standard convention the direction of projection from the plane of the ring system of substituting groups located at centres of asymmetry is usally designated by the Greek letters a and p. 

The a-substituting group is viewed as projecting beneath the ring plane and is conventionally represented by a broken line (dotted line). 

The P-substituting groups is viewed as projecting above the ring plane and is normally represented by a solid line. 

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STEROID NOMENCLATURE, NUMBERING, DOUBLE BONDS AND STEREOCHEMISTRY ... 

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