Alkylidene group
| Alkylidene group ( marked in blue ) |
 Methylidene group (often imprecisely also called methylene group) in propene. The methylidene group is marked in blue . |
 Ethylidene group in propene. The ethylidene group is marked in blue . |
 Isopropylidene group in 2-methyl-2-butene. The isopropylidene group is marked in blue . |
 Ethylidene group in 1,1-dichloroethane . The ethylidene group is marked in blue . |
An alkylidene group is the name given to a group of atoms in organic chemistry , the name of which is derived from the corresponding alkane. An alkylidene radical contains two fewer hydrogen atoms on the same carbon atom (defined as C-1) than the corresponding alkane. It is called a ' divalent residue' . The simplest alkylidene radical is the methylene group (–CH 2 -). This name comes from a time when the theory of chemical bonds was not yet developed. No distinction was made between tetragonal and trigonal carbon centers. This is why the H 2 C = group was also referred to as “methylene”. According to the IUPAC rules (rule A-4.1) this name is still allowed.
The term alkylidene group today implies that the carbon atom (C-1) to be linked is trigonal, i.e. H. sp 2 is hybridized and thus becomes part of a double bond . The H 2 C = group should therefore be referred to as the methylidene group . The ethylidene group has the structure H 3 C – HC =.
Nomenclature deviating from the IUPAC rule
A divalent radical derived from an alkane which contains two fewer hydrogen atoms on the same sp 3 -hybridized carbon atom than the parent compound, i.e. the alkane, is sometimes also referred to as an alkylidene group, for example in 1,1-dichloroethane . This terminology is understandable from the history of organic chemistry, but it should no longer be used today.
Individual evidence
- ^ H. Grünewald: International rules for chemical nomenclature and terminology , Volume 1, Verlag Chemie, Weinheim 1975, p. 12.
- ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 1: A-Cl. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1979, ISBN 3-440-04511-0 , p. 134.