Polymers

Beneath is a general formula for α-amino acids.RCH(NH₂)COOH

Different 'R-groups' make different amino acids.

Amino acids are amphoteric, which means that they can react with both acids and bases.

At an αamino acid's isoelectric point, it becaomes a zwitterion. A H is transferred from the OH group on the carboxillic acid to the amine group.

If the amino acid is in a solution more acidic than it's isoelectric point, it acts as a base, it accepts a proton onto the O group.

If the amino acid is in a solution more alkaline than it's isoelectric point, it acts as a acid, it donates a proton from the NH³ group.

In this example, the isoelectric point is pH 7

Polypeptides and proteins are long chains of amino acids.

These are formed by the OH group on one amino acid and a H off the N on the other, leaving to form a water molecule, and the C and the N form a peptide bond.

Because water is given out, this a condesation reaction, to split the chain up, it is a hydrolysis reaction.

Steroismers are species with the same structural formula but a different arrengement of atoms in space.

Optical isomers are steroismers that are non-superimposible mirror images of each other.

The two types of stereoisomerism are cis/trans and E/Z. It's cis/trans if there is a hydrogen on each carbon, E/Z is used if the groups have different molecular masses.

A chiral carbon is a carbon attached two four different groups, all amino acids have a chiral carbon execpt glycine (R-group = H).

Polyesters are made via condesation reactions, like the proteins were.

There are three main types:

1. A chain formed from two different types of monomer unit, a diol (alcohol group on each end) and a dicarboxillic acid (with two -COOH groups).

2. Or a chain formed from one diol monomer

3. Or formed from one monomer, with two groups, a COOH and a OH.

You just remove an OH from one and a H from the other and join the places where you took them from together.

Polyesters are used to make fibres.

These are made by removing a water molecule, and we're still on condensation reactions.

You take the OH off the COOH again, and a H off the NH₂ (getting the hang of this yet?)

There are two ways of making polyamides:

1. Two monomers, a diamide (two amine groups) and a dicarboxillic acid (have a guess!)

2.One monomer with a carboxillic acid group and a amine group.

Polyamides are used to make fibres. Kevlar and Nylon are polyamides.

Addition Polymerisation

This was in AS chemistry, but they still may ask you about it on the exam, basically, just lose the double bond and join it all together.

Condesation Polymerisation

Lose a small molecule such as water or hydrochloric acid (although anything but water is very unlikely to come up) and join the spare bonds together.

Hydrolysis is used to split up condensation polymers:

Base Hydrolysis NaOH/H₂O

In polyesters, the functional groups split up and change into COONA and OH. In polyamides, the functional groups split up and change into COONA and NH₂.

Acid Hydrolysis H₂O/H⁺

In polyesters, the functional groups split up and change into COOH and OH. In polyamides, the functional groups split up and change into COOH and NH₂.