Amino Acids,Polymers and Chirality

The body has 20 different amino acids, defined by their R-groups.

they are soluble in both acids and bases.

the isoelectric is the pH were there is no overall net charge. This causes a zwitterion to form, where the proton from the carboxylic group is transferred to the amine group. Every amino acid has a different isoelectric point.

r-groups are not affected at the isoelectric point, but they are at other pH's.

amide bonds

Condensation reaction removes a small molecule to join two larger ones. In amino acids, this creates a amide the bond and water is expelled. An amide bond includes an NH-C=O.

Two amino acids can form two different Dipeptides as the r-groups change it round.

Acid Hydrolysis

This splits amide bonds by water and reflux with concentrated acid, and the resulting amino acids are originated, due to the acids.

alkaline hydrolysis

With sodium hydroxide and 100℃. Resulting amino acids are actually salts of sodium.

Stereoisomerd have the same structural formula but a different arrangement of atoms in space. There are two types.

E/Z is shown around a double bond.

optical isomerism is shown around a chiral carbon, such as those in amino acids. These carbons have 4 different groups attached to them.

optical isomers are non-superimposable mirror images of each other. They are chemically different and al so rotate plane polarised light in different directions. If there are equal amounts of each chiral isometric, the mixture is called racemic.

In organisms, usually only one of the chiral isomers are biologically active, and only reacts with specific enzymes.

Condensation polymerization needs 

• monomers with two different functional groups.

Polyesters can be made with either a diol and a dicarboxylic acid, or one hydroxycarboxylic acid, which has a carboxylic and alcohol group. Both expel one molecule of water. This reaction makes an ester bond.

These can also be made using two different monomers (a diamine and a dicarboxylic) or one repeating carboxylamide, like amino acids. These reacR to make an amide bond and water.

an example of a polyamide is Kevlar which is very strong; used for bulletproof vests and helmets.

Addition: C=C bond is split and makes only the polymer and no side products.

Condensation: Either NH2 or OH reacts with COOH to  make amide/ester bond and water.

If the monomer contains double ***** = addition

if there are two monomers with different functional groups = condensation

Acid hydrolysis requires HOT AQUEOUS ACID.

when acid hydrolysing a polyamide REMEMBER the nitrogen will be PROTONATED!!!

Alkaline hydrolysis requires HOT AQUEOUS ALKALI and is faster than acidic hydrolysis.

CARBOXYLIC GROUPS will be a SALT.

Degradaability

New plastics such as poly(lactic) acid can under go hydrolysis.

photodegradability causes plastic to become weak and brittle when exposed to sunlight. C=O groups make this happen as they absorb light energy.