- Unsaturated hydrocarbons with one or more C=C bond

- General formula CnH2n

- C=C is a sigma and pi bond, where the pi bond is the overlap of p orbitals, and cannot rotate

- Trigonal planar around C=C

- Highly reactive as the pi bond is a region of high electron density

- e- deficient species (electrophlies) can attack the C=C

- pi bond has a smaller bond enthalpy than a sigma bond, so easier to break

1 of 5


- Stereoisomers have the same structural formula, but a different arrragment of atoms in space

- C=C does not rotate, so this is possible

- Types are E/Z and optical (see 27.2 for optical)

- E/Z requires C=C bond, and two different groups attached to each carbon 

- cis-trans are a certain kind where the group pair is the same on each carbon

cis/Z are where the highest priority are on the same side, and vice versa for trans/E

- CIP (Cahn-Ingold-Prelog) rules define priority - highest atomic number takes priority

2 of 5


- Addition reactions across the double bond saturates the alkene

- Hydrogen (Ni cat.) to make an alkane

-Halogen to make a dihaloalkane (bromine water test)

- Hydrogen halide to make a haloalkane (with asymmetrical molecules, two products formed)

- Steam (Acid catalyst-i.e. H3PO4) to make a alcohol (with asymmetrical molecules, two products formed)

3 of 5

13.4 Electrophilic addition

- Electrophile is a species that accepts a pair of e-, usually electron deficent with a +ve full or partial charge 

- Hydrogen halide-hydrogen has +ve dipole, accepts the e- pair 

- Halogen-dipole induced on halogen molecule

- Stability of formed carbocation is in order of: primary (least), secondary, tertiary

- Markownikoff's rule-Hydrogen will attach to the carbon with the most hydrogen atoms

4 of 5


- Addition polymerisation, where monomers are added to each other via the breaking of the C=C bond

- Monomer is the repeat unit, repeated times in the polymer

- Waste polymers processed by:

- Recycling (processed into new polymers)

- Burnt (for energy production)

- Chemical feedstocks (To make other plastics) 

- Halogenated plastics are toxic when burnt, so this must be removed

- Plant-based polymers are biodegradeable, with no toxic waste

- Photodegradeable polymers have bonds that weaken in light, beginning the breakdown of the polymers

5 of 5


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Functional Groups resources »