Editing Steroid (section)

=== Rings and functional groups ===
{{See also|Gonane|Sterane}}
[[File:gonane.png|thumb|120px|alt=Chemical diagram|class=skin-invert-image|[[Gonane]], perhydrocyclopenta[a]phenanthrene, the main structure of steroids, often referred to as the steroid nucleus.]]
[[File:5alpha5betaSteroidIUPAC.png|thumb|alt=Chemical diagram|class=skin-invert-image|Steroid 5α and 5β [[Stereoisomerism|stereoisomers]]<ref name = "IUPAC_steroids"/>{{rp|1786f}}]]
[[Gonane]], also known as steran or cyclopentanoperhydrophenanthrene, the nucleus of all steroids and sterols,<ref name="Rogozkin1991">{{cite book|vauthors=Rogozkin VA|chapter=Anabolic Androgenic Steroids: Structure, Nomenclature, and Classification, Biological Properties|title=Metabolism of Anabolic-Androgenic Steroids|chapter-url=https://books.auho.com/books?id=hRsnmJRF1WgC&pg=PA1|date=14 June 1991|publisher=CRC Press|isbn=978-0-8493-6415-0|pages=1–|quote=The steroid structural base is a steran nucleus, a polycyclic C17 steran skeleton consisting of three condensed cyclohexane rings in nonlinear or phenanthrene junction (A, B, and C), and a cyclopentane ring (D).1,2}}{{Dead link|date=March 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="Urich1994">{{cite book| vauthors = Urich K | chapter = Sterols and Steroids |title=Comparative Animal Biochemistry| chapter-url = https://books.google.com/books?id=GLbcWyeaCGQC&pg=PA624 |date=16 September 1994|publisher=Springer Science & Business Media|isbn=978-3-540-57420-0|pages=624–}}</ref> is composed of seventeen [[carbon]] atoms in carbon-carbon bonds forming four [[fused compound|fused ring]]s in a [[Chirality (chemistry)|three-dimensional shape]]. The three [[cyclohexane]] rings (A, B, and C in the first illustration) form the skeleton of a [[hydrogenation|perhydro]] derivative of [[phenanthrene]]. The D ring has a [[cyclopentane]] structure. When the two methyl groups and eight carbon [[side chain]]s (at C-17, as shown for cholesterol) are present, the steroid is said to have a cholestane framework. The two common 5α and 5β stereoisomeric forms of steroids exist because of differences in the side of the largely planar ring system where the hydrogen (H) atom at carbon-5 is attached, which results in a change in steroid A-ring conformation. Isomerisation at the C-21 side chain produces a parallel series of compounds, referred to as isosteroids.{{sfn|Greep|2013}}

Examples of steroid structures are:
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File:Testosteron.svg|alt=Chemical diagram|[[Testosterone]], the principal male [[Sex steroid|sex hormone]] and an [[anabolic steroid]]
File:Cholsäure.svg|alt=Chemical diagram|[[Cholic acid]], a [[bile acid]]
File:Dexamethasone structure.svg|alt=Chemical diagram|[[Dexamethasone]], a synthetic [[corticosteroid]] drug
File:Lanosterin.svg|alt=Chemical diagram|[[Lanosterol]], the [[biosynthetic]] precursor to animal steroids. The number of carbons (30) indicates its [[triterpenoid]] classification.
File:Progesteron.svg|alt=Chemical diagram|[[Progesterone]], a steroid hormone involved in the female menstrual cycle, pregnancy, and embryogenesis
File:Medrogestone.png|alt=Chemical diagram|[[Medrogestone]], a synthetic drug with effects similar to progesterone
File:Sitosterol structure.svg|alt=Chemical diagram|[[beta-Sitosterol|β-Sitosterol]], a plant or [[phytosterol]], with a fully branched hydrocarbon side chain at C-17 and an hydroxyl group at C-3
</gallery>
</div>
In addition to the ring scissions (cleavages), [[ring expansion|expansions]] and [[ring contraction|contractions]] (cleavage and reclosing to a larger or smaller rings)—all variations in the carbon-carbon bond framework—steroids can also vary:
* in the [[bond order]]s within the rings,
* in the number of methyl groups attached to the ring (and, when present, on the prominent side chain at C17),
* in the functional groups attached to the rings and side chain, and
* in the [[Chirality (chemistry)|configuration]] of groups attached to the rings and chain.<ref name = "Lednicer_2011"/>{{rp|2–9}}
For instance, [[sterol]]s such as cholesterol and lanosterol have a [[hydroxyl group]] attached at position C-3, while [[testosterone]] and [[progesterone]] have a carbonyl (oxo substituent) at C-3. Among these compounds, only [[lanosterol]] has two methyl groups at C-4. Cholesterol which has a C-5 to C-6 double bond, differs from testosterone and progesterone which have a C-4 to C-5 double bond.

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| [[File:Cholesterol lettering numbering.svg|thumb|alt=Chemical diagram|class=skin-invert-image|[[Cholesterol]], a [[prototype|prototypical]] animal sterol. This structural [[lipid]] and key steroid [[biosynthesis|biosynthetic]] precursor.<ref name = "IUPAC_steroids"/>{{rp|1785f}}]]
| [[File:Cholestane.svg|thumb|alt=Chemical diagram|class=skin-invert-image|5α-[[cholestane]], a common steroid core]]
|
|}