3.3.1 and 3.3.2 Alkenes Flashcards
Alkenes
General formula
CnH2n
Alkenes made up of
hydrocarbons
Alkenes are
saturated or unsaturated?
unsaturated
Alkenes
Unsaturated hydrocarbons with double bonds between one or more of the carbon atoms.
Alkenes reactivity?
why
pretty reactive
due to 2 pairs of e-s in the double bond so high e- density
Electrophilic addition reactions
double bonds open up and atoms are added to the carbon atoms
Why does electrophilic addition occur
plenty of electrons in the double bond so easily attacked by electrophiles
Electrophiles are …
electron pair acceptors
What are electrophiles attracted to
2
negative charge
polar molecules
Electrophile
definition
Lone pair acceptors
Addition
definition
Reaction which increases the number of substituents
Test for alkenes
bromine water test
Bromine water test
Add an alkene to bromine water in a test tube with a bung
shake
if the solution goes from orange to colourless an alkene is present
How does the bromine water test work
bromine is added across the c=c bond making a dibromoalkane which is colourless
electrophilic addition
Halogenoalkanes formed by
alkenes and hydrogen halides (eg: HBr)
electrophilic addition
Carbocation intermediate
Amount of each product formed depends on how stable the carbocation formed in the middle of the reaction is
Carbocation?
a molecule with a carbon atom which has 3 bonds and a positive charge
Unsymmetrical alkene with hydrogen halide
carbocation intermediate
or
more stable carbocations (with more alkyl groups)
Carbocations with more alkyl groups
are more stable
Alkyl groups
alkanes with with a hydrogen removed
eg: methyl CH3-
Alkenes reactions with H2SO4
alkenes react with cold, concentrated sulphuric acid to form alkyl hydrogen sulfates
How to convert alkyl hydrogen sulphates into alcohol
add water and warm the reaction mixture
reaction with an unsymmetrical alkene
mixture of products
