Alkenes: Nomenclature of Hydrocarbon Compounds

University:
Colorado State University
Course:
CHEM 107 | Fundamentals of Chemistry (GT-SC2)
Academic year:

2023
Views:

438

Pages:

3
Author:

Hizkia L

Nomenclature of Hydrocarbon Compounds : Alkenes a. Alkene General Formula Alkenes are unsaturated aliphatic hydrocarbons having one double bond (C=C). Compounds with two double bonds are called alkadienes, those with three double bonds are called alkatrienes, and so on. What is the general formula for alkenes? Look at the compounds below then compare! What conclusions did you draw? Yes, that's right, it turns out that alkenes have two fewer hydrogen atoms attached than alkanes. Since the general formula for alkanes is Cn H2n + 2, the general formula for alkenes is (James E. Brady, 1990): CnH2n _ b. Alkene Nomenclature 1) Alkenes are straight chains The names of straight-chain alkenes correspond to the names of the alkanes, but by changing the -ane ending to -ene. Example: • C2 H4 ethene • C3 H6 propene • C4 H8 butene 2) Branched chain alkenes The order of naming is: a) Choose the parent chain, which is the longest carbon chain that contains a double bond. Example: b) Numbering, with numbering rules starting from one end of the main chain, so that the double bond gets the smallest number (not based on branch position). Example: b) Naming, in the following order: - the C atomic number that binds the branch – the name of the branch - the C atomic number of the double bond - the name of the main chain (alkene) Example : c. Alkene isomers Alkenes have two isomers as follows. 1) Structural isomerism Structural isomerism, namely isomerism that occurs when the molecular formula is the same, but the structural formula is different. The isomers in alkenes begin to be found at C4 H8 and continue to higher terms. Notice the example below! a) C4 H8 has three kinds of isomers, namely: b) C5 H10 has five kinds of isomers, namely: \ 2) Geometry isomerism Geometry isomerism, namely isomerism that occurs due to differences in the orientation of the groups around the C double bond. Example: 2–butene has two geometric isomers, namely cis–2–butene and trans–2–butene. The condition for the occurrence of geometric isomers is when each double bonded carbon atom binds 2 different atoms or 2 groups, so that if the bonded atoms or groups switch places, the structure will be different.