F324 - Amino acids and polymers

Detailed notes on this part of F324 including OCR textbook diagrams as well as reagents & conditions.

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Polymers and Amino Acids
Amino Acids
AlphaAmino Acids
amino acids have a carboxylic acid group and an amine group attached to the same
carbon atom, which is also a chiral centre.
Isoelectric point: the pH at which an amino acid has no charge.
Zwitterion: A molecule with net charge of zero, but negative and positive charges on different parts within the structure.
A proton is transferred from the COOH to the NH 2. The zwitterion has no overall charge as the COO
cancels out the NH 3
The isoelectric point is the pH at which there is no net electric charge. This + / charge increases the intermolecular forces
between amino acids considerably. They are often described as having unusually high melting points and their pH is around 6.
This is due to the fact that the COOH is actually slightly more acidic than the NH2 is basic.
The rest of the molecule (the R group) also has an influence on how acidic or how basic the ­COOH and ­NH2 groups are
which means that every amino acid will have a slightly different isoelectric point.
Polypeptides and Proteins
Condensation Reactions
The functional group (in purple) is an amide group (CONH) ­ and this makes a peptide bond.
A different dipeptide can be made by joining them the other way round, i.e. alanine provides the ­OH and glycine the ­H for the
eliminated water molecule to form.
A polypeptide is formed when more than 50 amino acids are joined together by peptide bonds, and because this is a
condensation reaction, each linkage is eliminating a water molecule.

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Polymers and Amino Acids
Acid Hydrolysis
Reagents and Conditions: heat under reflux, concentrated HCl
Alkali Hydrolysis
Reagents and Conditions: hot aqueous NaOH
Condensation Polymerisation
A polyester is made from a diol and a dicarboxylic acid.
It is described as a condensation reaction as water is eliminated as
the ester link is formed. Used in the manufacture of carpets.
Terylene is made from the reaction between the monomers
ethane1,2diol and benzene1,4dicarboxylic acid.…read more

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Polymers and Amino Acids
reaction as water is eliminated as the amide link is formed. Used in the manufacture of clothing.
Kevlar is another polyamide made from the monomers
benzene1,4dioic acid and benzene1,4diamine. It is a very
strong polymer used in fire and bullet proof vests and crash
Because amide links in polyamides and ester links in polyesters can be hydrolysed, they are biodegradable. These links are
found in nature so there are fungi and bacteria that can degrade them.…read more

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Polymers and Amino Acids
Most plastic packaging is addition polymers which will not degrade in landfill sites. Environmental demand means we have had
to produce biodegradable plastics. These have chemical bonds that will hydrolyse (similar to polyesters and polyamides). A
polymer based on tapiocha starch will decompose in only 28 days when buried.
Photodegradable polymers
These become weak when exposed to light. The polymers can be blended with light sensitive catalysts which will catalyse the
decomposition of the polymer.…read more


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