3.4 Alkenes Flashcards
C-C single bond
Sigma
C=C double bond
Sigma and Pi
Is C-C or C=C stronger?
C=C is stronger as it is composed of a sigma and pi bond
Is a sigma or a pi bond more reactive?
A pi bond as it requires less energy to break
Why is there non rotation around a C=C bond?
The pi bond is formed by overlap of the p orbital
If there was any rotation, the p orbitals wouldn’t overlap and the pi bond would break
Electrophile
Electron pair acceptor
Types of electrophiles
Hydrogen halides
Halogens
Sulphuric acid
Hydrogen halides
HCl
Her
Halogens
Cl2
Br2
Sulphuric acid
H2SO4
Electrophilic addition with hydrogen halides
Reagent : HCl, HBr
Conditions : none
Product : Haloalkane
Double bond to single bond
2 steps
Alkyl groups
Methyl
Ethyl
Propyl
Positive inductive effect
Ability to release electron density through a covalent bond
Primary carbocation
1 alkyl group
Least stable
Tertiary carbocation
3 alkyl groups
Most stable
Why are tertiary carbocations more stable than primary carbocations?
More positive inductive effect from 3 alkyl groups compared to 1 in a primary carbocation
Major product
Higher quantity
Produced from a more stable carbocation
Electrophilic addition with halogens
Reagent : Cl2, Br2
Conditions : none
Product : Haloalkane
Two steps
Why do bromine molecules react with the double bonds in alkenes?
The C=C is electron rich, it induces a dipole in Br2, the delta + Br is attracted to the C=C
Test for alkenes
Add bromine water
Orange to colourless
Electrophilic addition with sulphuric acid
Reagent : H2SO4
Conditions : None
Product : Alkyl hydrogen sulphate
What does H2SO4 act as in electrophilic addition?
A catalyst
Alkyl hydrogen sulphate + H2O
Alcohol + H2SO4
Addition polymer
Long chain of monomers
Ethene monomer
Polythene polymer
