4.2.1 Amino Acids and Chirality Amino acids Candidates should be able to: (a) state the general formula for an -amino acid as RCH(NH2)COOH; (b) state that an amino acid exists as a zwitterion at a pH value called the isoelectric point; (c) state that different R groups in -amino acids may result in different isoelectric points; (d) describe the acid–base properties of -amino acids at different pH values; Peptide formation and hydrolysis of proteins (e) explain the formation of a peptide (amide) linkage between -amino acids by condensation and subsequent condensation polymerisation to form polypeptides and proteins (f) describe the acid and the alkaline hydrolysis of proteins and peptides to form -amino acids or carboxylates Optical isomerism (g) describe optical isomers as non-superimposable mirror images about an organic chiral centre: four different groups attached to a carbon atom; (h) identify chiral centres in a molecule of given structural formula; (i) explain that optical isomerism and EIZ isomerism are different types of stereoisomerism. 4.2.2 Polyesters and Polyamides Condensation polymers Candidates will not be expected to recall the structures of synthetic polyesters and polyamides or their monomers. Candidates should be able to: (a) describe condensation polymerisation to form (i) polyesters, eg Terylene from benzene-1,4- dicarboxylic acid and ethane-1,2-diol, poly(lactic acid) from 2-hydroxypropanoic acid (lactic acid) (ii) polyamides, eg nylon-6,6 from 1,6- diaminohexane and hexane-1,6- dicarboxylic acid, Kevlar from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid; (b) compare condensation polymerisation with addition polymerisation (c) suggest the type of polymerisation from: (i) a given monomer or pair of monomers, (ii) a given section of a polymer molecule; (d) identify the monomer(s) required to form a given section of a polymer (and vice versa); (e) state the use of polyesters and polyamides as fibres in clothing; Hydrolysis and degradable polymers Poly(lactic acid) is used for waste sacks, packaging, disposable eating utensils and medical applications such as internal stitches. Production of degradable polymers from renewable resources. (f) describe the acid and the base hydrolysis of polyesters and polyamides; (g) outline the role of chemists in minimising environmental waste by development of degradable polymers, similar in structure to poly(lactic acid) (h) explain that condensation polymers: (i) may be photodegradable as the C=O bond absorbs radiation, (ii) may be hydrolysed at the ester or amide group. 4.2.3 Synthesis Synthetic routes Candidates should be able to: (a) for an organic molecule containing several functional groups: (i) identify individual functional groups, (ii) predict properties and reactions; (b) devise multi-stage synthetic routes for preparing organic compounds; Chirality in pharmaceutical synthesis Requirement for chiral drugs and medicines to minimise side effects, for economical reasons and to reduce risk to companies from litigation. Examples of chemical chiral synthesis use cyclic strained molecules, reagents fixed to a polymer support with reactants flowing over them, and supercritical CO2. (c) explain that the synthesis of pharmaceuticals often requires the production of a single optical isomer; (d) explain that molecules prepared synthetically in the laboratory often contain a mixture of optical isomers, whereas molecules of the same compound produced naturally by enzymes in living systems will often be present as one optical isomer only; (e) explain that the synthesis of a pharmaceutical that is a single optical isomer: (i) increases costs due to difficulty in separating the optical isomers, (ii) reduces possible side effects and improves pharmacological activity; (f) explain that modern synthesis of a pharmaceutical with a single optical isomer is often carried out: (i) using enzymes or bacteria which promote stereoselectivity, (ii) using chemical chiral synthesis or chiral catalysts, (iii) using natural chiral molecules, such as Lamino acids or sugars, as starting materials.