13.3 Reactions of alkenes
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Are alkenes more or less reactive than alkanes
MUCH MORE due to presence of the π-bond π-electrons are more exposed than electrons in σ-bond electrons π-bond readily breaks and alkenes undergo addition reactions
Alkenes undergo many addition reactions for example with:
Hydrogen in the presence of a nickel catalyst Halogens Hydrogen halides Steam in the presence of an acid catalyst Each involves addition of small molecule across double bond causing the π-bond to break and for new bonds to form
What is hydrogenation
The addition reaction in which hydrogen is added across a double bond
What can the reaction of alkenes with bromine be used to identify
Identify if there is a C=C bond present and the organic compound is unsaturated
What happens when bromine water is added dropwise to a sample of an alkene
Bromine adds across the double bond Orange colour disappears indicating the presence of a C=C bond
What happens when bromine water is added dropwise to a saturate compound
There is no addition reaction and no colour change
What do alkenes react with gaseous hydrogen halides at room temperature to form
Haloalkanes If alkene is a gas, then the reaction takes place when the two gases are mixed, if the alkene is a liquid, then the hydrogen halide is bubbled through it Also react with concentrated hydrochloric or hydrobromic acid
When are alcohols formed
When alkenes react with steam Steam adds across the double bond Used to produce ethanol from ethene Two possible products