Page - (000023) - in Biomedical Chemistry: Current Trends and Developments

and bioorganic transformations. Electrophiles are either positively charged or neutral and have at least one positively polarised, electron- poor atom. Conversely, nucleophiles are either negatively charged or neutral and have a lone pair of electrons that can be donated. Table 1.1.3: Relative acidity strengths of some functional groups and common reactants. Functional group Example pKa carboxylic acid 4.76 ammonium 9.26 alkylthiol CH3SH 10.3 alkylammonium ion 10.66 β-keto ester 10.6 water H2O 15.74 alcohol CH3CH2OH 16.0 ketone 19.3 thioester 21 ester 25 Scheme 1.1.4: Example of a biochemical reaction involving a Lewis acid and a Lewis base. Reversible conversion of carbon dioxide to hydrogen carbonate can occur rapidly in the active site of a carbonic anhydrase, the equilibrium being regulated by factors such as pH. 1.1.3 Stereoisomerism and Chirality Stereoisomers having the spatial orientation of bonds as their unique