The beta-lactam ring is highly reactive and enables penicillins to be effective antibacterials. The general structure of penicillin is given in table 20 of the data booklet. Explain, in terms of hybridization and bond angles, why the beta-lactam ring is strained.

Cytovaricin is an antibiotic that is produced using a chiral auxiliary. Suggest why it may be necessary to use a chiral auxiliary during its production.

Describe how a chiral auxiliary is involved in the synthesis of a drug.

C=O carbon is \({\text{s}}{{\text{p}}^{\text{2}}}\) hybridized and others are \({\text{s}}{{\text{p}}^{\text{3}}}\);

(normal) bond angles (120° and 109.5°) cannot be achieved in ring;

Accept bond angles in the ring are 90.

only one enantiomer is active/has required effect / one enantiomer may have adverse effects;

Accept stereo/optical isomer, but not just isomer.

chiral auxiliary attaches to non-chiral compound;

creates desired stereochemical conditions for reaction / ensures only one isomer is produced / OWTTE;

auxiliary removed/recycled after reaction (to leave desired product);

Award [1 max] for making the compound chiral/optically active / OWTTE.

Many students could correctly explain the mode of action of penicillins, but often explanation of the strain in the bond angle failed to go into the required depth concerning the hybridization of the atoms in the four-membered ring. An encouragingly large number of candidates could explain how chiral auxiliaries are used in drug synthesis, but sometimes their response to the first part of this question failed to identify why it is sometimes necessary to use such an elaborate procedure. Many students could give the mode of action of antiviral drugs, though sometimes these responses lacked the required precision.

Many students could correctly explain the mode of action of penicillins, but often explanation of the strain in the bond angle failed to go into the required depth concerning the hybridization of the atoms in the four-membered ring. An encouragingly large number of candidates could explain how chiral auxiliaries are used in drug synthesis, but sometimes their response to the first part of this question failed to identify why it is sometimes necessary to use such an elaborate procedure. Many students could give the mode of action of antiviral drugs, though sometimes these responses lacked the required precision.

Many students could correctly explain the mode of action of penicillins, but often explanation of the strain in the bond angle failed to go into the required depth concerning the hybridization of the atoms in the four-membered ring. An encouragingly large number of candidates could explain how chiral auxiliaries are used in drug synthesis, but sometimes their response to the first part of this question failed to identify why it is sometimes necessary to use such an elaborate procedure. Many students could give the mode of action of antiviral drugs, though sometimes these responses lacked the required precision.