Alkenes Flashcards
alkenes
a homologous series of unsaturated hydrocarbons
features of a homologous series
- have the same general formula
- differ by CH[2] in molecular formula from neighbouring compounds
- show a gradual variation in physical properties
- have similar chemical properties
molecular formula definition
chemical formula showing the actual number of atoms of each element in a molecule
general formula of alkenes
C[n]H[2n]
functional group of alkenes
C=C
not all the carbon atoms in a compound will have double bonds, all except one bond can be single bonds
complete combustion of alkenes
- carbon is oxidised to CO2
- H is oxidised to water vapour
C[2]H[4] + 3O[2] _> 2CO[2] + 2H[2]O
alkenes and bromine
react with bromine to form a colourless compound
ethene + bromine -> dibromoethane
C[2]H[4] + Br[2] -> C[2]H[4]Br[2]
Why do alkenes react with bromine?
they are unsaturated
test for alkenes (to distinguish from alkanes)
- add a few drops of bromine water
- stays orange in an alkane
- is decolourised in an alkene
first four names
ethene
propene
butene
pentene
(methene can’t exist as one carbon can’t have a double bond)
example diagram
e.g.
(propene)
three carbons in a line
one double bond, one single bond
surrounded by Hs, but the carbons with a = only have one
isomers
have the same number of carbons and hydrogens but are arranged differently
Name all the different isomers of Butene
But-1-ene
But-2-ene
What does but-1-ene/but-2-ene look like as a structural formula?
it has the double bond between the first and second carbon atoms
but-2-ene has the double bond between the second and third carbon atoms
Why aren’t there more isomers of butene?
if you turn it around it doesn’t matter if the bond is in first or last place, it is still but-1-ene
each molecule only has half as many isomers as it does carbons
