Addition polymerisation and Alkenes

Polymer

long molecular chain built up from monomer units (high Mr)

Monomer

small molecule that combines with many other monomers to form a polymer

based on different alkenes

Unsaturated - with double bond

Addition polymer

long molecular chain, formed by repeated addition reactions of many unsaturated alkene molecules / monomers

List the methods of dealing with polymer waste, to reduce landfill waste?

Sort into types and recycle

Combustion for energy

Organic feedstock

How can toxic fumes such as HCl be removed?

Neutralise by adding a base, e.g. NaOH

How have chemists developed solutions to reduce landfill waste?

Designed biodegradable / compostable polymers

Alkene

The general formula for alkenes is Cn H2n

The carbon-carbon double bond is a functional group and is responsible for the reactivity of alkenes.

Alkenes are described as unsaturated hydrocarbons

List all the formulas you need to know for unsaturated hydro carbons

Alkenes CnH2n

Cycloalkenes CnH2n-2

Arenes eg benzene C6H6

State and explain the shape around each C atom in C=C

3 bonding regions

Electron pairs repel equally

Therefore shape is trigonal planar

Angles are 120 degrees

Sterioisomer

Stereoisomers have (the same molecular and) the same structural formula but a different arrangement of atoms in space (spatial arrangement of the atoms).

E/Z isomers occur when alkenes have

2 different groups on each C atom in the C=C

because of restricted rotation around the double bond

How does prority work for E/Z isomers

If the 2 highest priority groups are on the same ‘side’ of the double bond it is a Z isomer

If the 2 highest priority groups are on the opposite ‘side’ of the double bond it is an E isomer

What is Cis-Trans

Cis-trans is a sub-set of E/Z:

E/Z isomers with a H atom on each C in the C=C are also known as cis-trans

isomers

Z isomers are cis isomers

E isomers are trans isomers

Cahn-Ingold-Prelog rules

Robert Sidney Cahn, Christopher Kelk Ingold and Vladimir Prelog

assigned priority to groups for classifying E / Z, according to highest

atomic number(s):

If the 2 highest priority groups are on the same side of C=C => Z

If the 2 highest priority groups are diagonally across the C=C => E.

How is a double bond made

In a double bond one of the C-C bonds is a σ-bond (Covalent)

The second part of the double bond is called a π-bond.

Whats a π-bond

The π-bond is caused by the sideways overlap of p-orbitals.

The π-bond is a shared pair of electrons (one from each C atom).

The π-bond prevents rotation around the C=C.

Electrophile

Electron pair acceptor

The reactivity of alkenes

Alkenes are more reactive than alkanes because of the π-bond. When alkene reacts, π bond breaks, σ bond intact Alkenes are very reactive because the π-bond is weaker than the σ-bond.

Bromine test

Adding bromine to an alkene changes the orange bromine solution to a

colourless solution.

Markownikoff rule

The major product formed when a hydrogen halide is reacted with an unsymmetrical alkene is the one that is formed from the most stable carbocation intermediate:

3o > 2o > 1o.