Parent hydride
In IUPAC nomenclature, a parent hydride is an unbranched acyclic or cyclic structure to which only hydrogen atoms are attached. Parent hydrides are parent structures that contain one or more hydrogen atoms. They are the basic structures used in substitutive nomenclature.
The bonding number of a skeletal atom in a parent hydride is the sum of the total number of valence bonds to adjacent skeletal atoms, if any, and the number of attached hydrogen atoms. In SH2, for example, S has bonding number 2.
Parent hydrides are compounds with an unsubstituted skeleton, thus with only hydrogens attached to it. They have a defined standard population of hydrogen atoms. Acyclic parent hydrides are always saturated and unbranched. Cyclic parent hydrides are usually either fully saturated or fully unsaturated (containing the maximum number of double bonds). Some combinations of rings or combinations of cyclic and acyclic hydrides may be partially saturated. All elements have 'standard bonding numbers', that is for nitrogen and phosphorus 3, for carbon and silicon 4, etcetera.
The names of parent hydrides are ending with 'ane', analogous with the nomenclature for alkanes. Unsaturated hydrides are given the ending 'ene' or 'yne', for example, 'diene' for two double bonds. For non-carbon homocyclic compounds with 3 to 10 membered rings the Hantzsch–Widman nomenclature is preferred. Derivatives of parent hydrides get the name of the parent hydride, along with prefixes or suffixes appropriate to the substituents that replace the hydrogen atoms.
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