Chemical Properties Of Steroids

It is a fused tetracyclic compound composed of three six carbon cyclohexane rings (A, B, C) and one five carbon ring (D). The order of carbon atom numbering is shown in.
The number and position of double bonds in various natural steroid molecules, the type, number, and position of substituent groups, the configuration between substituent groups and cyclic nuclei, and the configuration between rings all vary.
The six carbon rings A, B, and C in natural steroid molecules all adopt a "chair like" conformation (cyclohexane structure), which is the most stable conformation (the only exception being that the A ring in estrogen molecules is an aromatic ring with a planar conformation).
The junction between ring A and ring B can be cis or trans, while the C/D junction is generally trans; Only cardiac glycosides and toad venom are exceptions.
The orientation of the substituent groups connected to the carbon atoms of the four ring skeleton of steroids is represented by α - or β -: those located above the skeleton plane are represented by β (solid line), and those located below are represented by α (dashed line). For example, the hydroxyl group on cholesterol molecule C-3, the two angular methyl groups C-18 and C-19, and the side chains are all beta oriented.