| 词条 | Parent hydride | ||||||||||||||||||||||||||||||||||
| 释义 |
In IUPAC nomenclature, a parent hydride is an unbranched acyclic or cyclic structure to which only hydrogen atoms are attached.[1] 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.[2] Nonstandard bond numbers (see table below for standard bond numbers) are indicated using lambda nomenclature. Parent hydrides in substitutive nomenclatureParent 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.[3] Group 14 to 17 elements and boron have 'standard bonding numbers', that is for nitrogen and phosphorus 3, for carbon and silicon 4, as shown below in the table. Nonstandard bond numbers are indicated using λn as a prefix. For example, PH5 is named λ5-phosphane. 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 are named by appending prefixes or suffixes to the name of the parent hydride to indicate the substituents that replace the hydrogen atoms. Parent hydrides are used in both the organic nomenclature, and inorganic nomenclature systems.[4]
ExamplesExamples of mononuclear parent hydrides (with a single skeletal atom) are: BH3 (borane), CH4 (methane; not carbane[5]), SiH4 (silane), NH3 (azane), PH3 (phosphane), H2S (sulfane) and H2O (oxidane).[6]
Reactions and structureParent hydrides are useful reference compounds but nonetheless often nonexistent or unstable. Group III parent hydrides exist only under extraordinary conditions. Borane dimerizes irreversibly. Gallane and heavier congeners polymerize, sometimes with loss of hydrogen. Plumbane and bismuthane are unstable. For group V, stibane, indigane, thallane are also unstable. In many cases the permethyl compounds are stable. See also
References1. ^IUPAC Gold Book definition: parent hydride 2. ^IUPAC Gold Book definition: bonding number 3. ^Preferred IUPAC Names Provisional Recommendation:Parent hydrides Chapter 2, par. P-20. 4. ^Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 (Red Book) Par. IR-6 Parent Hydride Names and Substitutive Nomenclature - Full text PDF 5. ^The name 'carbane' is used to form derivatives, such as carbene and carbyne, and it is also an acceptable synonym for methane (although it is not the preferred IUPAC name [PIN]). However, it is not the parent hydride name for ane nomenclature. 6. ^Nomenclature of Inorganic Chemistry-IUPAC Recommendations 2005 Red Book 2005.pdf IR-6.1, p.84 1 : Chemical nomenclature |
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