Constancy
In chemistry, permanence describes the position of two functional groups in relation to one another within an organic compound .
Here mean
- α- position or α-position : the functional groups are on the same carbon atom ( geminal ). Examples are α-hydroxycarboxylic acids or α-amino acids .
- β- position or β-position : the functional groups are located on two adjacent carbon atoms ( vicinal ). Examples are β-alanine , β-oxocarboxylic acids such as β-oxobutanoic acid (acetoacetic acid).
- γ- position or γ-position : the functional groups sit on carbon atoms, which are separated by another carbon atom. Examples are γ-diketones or γ-hydroxybutyric acid (according to IUPAC : 4-hydroxybutanoic acid).
- δ- position or δ-position : the two functional groups are attached to carbon atoms that are separated by two additional carbon atoms. Examples are the δ- lactones and δ- thiolactones .
- ε- position or ε-position : the two functional groups are attached to carbon atoms, which are separated by three additional carbon atoms. Examples are about ε- caprolactone or ε- caprolactam .
The designation ω-position has a special, non-systematic meaning for the maximum possible distance between two functional groups in a given molecule. In the case of unsaturated fatty acids , the last carbon atom is referred to as the ω-position, see nomenclature of unsaturated fatty acids .
The Greek letters used here to indicate the relative position of functional groups have a different meaning than the descriptors " α- " and " β- " which are used to characterize the stereochemical configurations of carbohydrates .
Ortho , meta , para for benzene derivatives
In benzene derivatives, the relative position of two substituents is described by the prefixes ortho , meta and para or " o- ", " m- " and " p- " for short :
- ortho position (corresponds to β position) denotes the position on two adjacent ring atoms, see for example phthalic acid ( ortho- benzenedicarboxylic acid). In the IUPAC nomenclature, this corresponds to a 1,2-substitution.
- meta- position (corresponds to γ-position) denotes the position on two ring atoms, which are separated by another atom, for example in resorcinol ( meta -dihydroxybenzene). Such a substitution pattern is called 1,3-substitution in the IUPAC nomenclature.
- para- position (corresponds to δ-position) denotes the position on two ring atoms, which are separated by two further atoms and are therefore exactly opposite each other on the six-membered benzene ring. Examples are hydroquinone ( para -dihydroxybenzene) or terephthalic acid ( para -benzenedicarboxylic acid). This substitution pattern is called 1,4-substitution in the IUPAC nomenclature.
Individual evidence
- ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, p. 615, ISBN 3-342-00280-8 .