What do I call an alkene

Alkenes nomenclature

Like it that Geneva nomenclature system prescribes, the names of the compounds are derived from the structure of the molecules. The following rules apply to the naming of the alkenes:

1. The Ending the name of the alkenes is:

This final syllable is therefore the sign of a double bond in the molecule.


2. For the initial members of the homologous series of alkenes can use the common names that have been introduced Ethylene, propylene and Butylene but one should also use the names Ethene, propene and But-en use. The name of the alkenes, derived from the corresponding alkanes, also applies to the higher members of the alkenes. From the C5-Connection an are used for the parent compound, as with the alkanes, the Greek or Latin numerals as initial syllables and the final syllable -en appended, e.g. B. Pent-en, hex-en, hept-en, oct-en etc.


3. The Trunk connection determines the longest straight chain of carbon atoms in the molecule (Main chain). However, it must be taken into account here that the double bond must lie in this main chain.



4. The Position of the double bond is indicated by numbers. The numbering of the carbon atoms begins at the end of the main chain to which the double bond is closest. The carbon atom followed by the double bond is identified. The number is placed after the ending -en (with a hyphen and brackets).

Example: pentene (2) and octene (3)


5. At branched connections will the Side chains as named for the alkanes. The numbering is fixed by the position of the double bond; the position of the side chain is indicated by the number of the carbon atom to which the group is attached.

Example: 4-methyl-pent-en- (1) and 3-methyl-5-ethyl-oct-en- (2)


6. In the case of double bonds in the middle (on the carbon atom 2, 3, ...), the cis-trans isomers must be specially named. The appropriate designation cis or trans is placed in front of or after the name of the compound.

Example: cis-pentene- (2), or hepten- (3), trans


7. Instead of the numbers 1, 2, 3 ... you can still find the outdated designations α, β, γ ... An α-alkene is therefore a compound with a terminal double bond. The designation n-pentene- (2) for the unbranched compound or i-pentene- (1) for the branched compound should also no longer be used, as they are not always unambiguous.