I completed the A-Level in one year teaching most of the course to myself, earning an A overall. This is a summary of the textbook chapter with all details you will need for the exam, I found this most useful as it streamlines the information and keeps everything I needed in one place. Comparing ma...
Alkenes: an unsaturated hydrocarbon that contains at
least one carbon-carbon double bond. CnH2n
• the double bond is planar with atoms at 120°,
• Has a fixed rotation due to the double bond, there’s 1. Br has an instantaneous dipole as it approaches the
overlapping p-orbitals making a pi-bond and so the alkene, producing a slightly positive atom.
bonds cannot rotate, creating restricted rotation. 2. Double bond breaks and C atom bonds with one of the
Br atoms, causing a repulsion with the electrons of the
other Br atom forcing the Br-Br bond to break.
3. The halide ion is attracted to the carbocation and so
donates the lone pair of electrons to form a dative bond
• Only has van der waals so has similar physical and remove the charge.
properties to alkanes 4. Produces a dihalogenoalkane
• Can be attacked by electrophiles
Naming-take the root of the hydrocarbon chain and
then add the suffix -ene
The fixed rotation means that the alkanes have isomers.
Positional isomers as the double bond will move,
Geometric isomers due to E-Z isomerism.
Z=same side of double bond, 1. The electrons in the double bond are attracted to the H
E=different sides of the double bond atom in sulphuric acid
To find which groups have the priority you calculate the 2. Double bond breaks and creates a dative bond with H
atomic number/ molecular mass, the larger groups have atom, forcing O-H bond to break producing -OSO3H
priority when differentiating if it’s E/Z. 3. The -OSO3H bonds to the carbocation donating the
lone pair of electrons in a dative bond to remove the
charge
14.2 Reactions of alkenes: 4. The addition of water causes H2SO4 to recombine
proving it’s a catalyst
Can burn in oxygen, however not used as fuels as their 5. Produces an alcohol
reactivity is more useful. Can react with water to produce an alcohol needs steam
Electrophile: positively charged ions / atoms that accept and phosphoric acid as a catalyst.
a pair of electrons eg. H+
In electrophilic addition the double bond is broken to Positive Inductive Effect-
form a positive C atom so another species bonds to Alkyl groups are electron releasing, which stabilises the
remove the charge. compound / carbocation, the reactions will favour the
reaction with the most stable carbocation and product.
Primary Secondary Tertiary
+ + +
R - C -H R-C-R R-C-R
1. The electron rich double bond is attracted to the H R
H
positive H atom in the hydrogen halide.
2. Double bond breaks and donates electrons to the H This means you are more likely to find the functional
atom forming a dative bond, causing the highly group towards the centre of the chain as the carbocation is
polar H-Br bond to break, creating a halide ion more stable. This idea only occurs with an asymmetric
3. There’s now a positive carbon compound called a alkene or an asymmetric electrophile.
carbocation, this attracts the halide ion
4. The halide ion donates the lone pair of electrons to
the positive C atom forming a dative bond 14.3 Addition Polymers:
5. Produces a halogenoalkane
Monomer: a repeating unit that can bond together to form
long, repeating chains
Polymer: large chains made from repeating monomers
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