Section 7.1     Carbonyl-containing functional groups play important structural and functional roles in biological macromolecules and in drugs.

Section 7.2     A carbonyl (C=O) bond is composed of a σ bonding component and a π bonding component and is analogous to the C=C bond in ethylene. Carbonyl bonds are electrophilic and their relative reactivity is impacted by both electronic and steric factors.

Section 7.3     Electronic effects on carbonyl reactivity are mediated through inductive and resonance effects. The reactivity of carbonyl-containing functional groups varies widely depending on the nature of the substituent on carbon. Biologically relevant examples are shown below in order of their reactivity with nucleophlies.

Section 7.4     The hydration reactions of aldehydes and ketones proceed via distinct mechanisms at acidic, neutral, or basic pH. In general, C–O bond formation is slow compared to proton transfer (acid-base) reactions.

Section 7.5     The reaction of aldehydes and ketones with alcohols is similar to hydration but can involve a second addition step to afford an acetal or ketal. A special type of acetal is that found in the glycosidic bond that links sugars into di-, tri-, or polysaccharides.

Section 7.6     Reactions of amines with carbonyl species leads to imines or enamines depending on whether a primary or secondary amine is undergoing reaction. Imine and enamine formation proceeds through tetrahedral intermediates.

Section 7.7     Oximes and hydrazones are formed from the reaction of a hydroxylamine or hydrazine with an aldehyde or ketone. Close cousins of imines, oximes and hydrazones are generally more stable to hydrolysis due to their reduced basicity as compared to imines.

Section 7.8     Ester hydrolysis can be promoted under either acidic or basic conditions. Protonation of the ester carbonyl is required under acidic conditions where neutral water is the nucleophile. Amide hydrolysis is most favorable under acidic conditions where amine protonation favors breakdown of the tetrahedral intermediate.

Section 7.9     Proteases are enzymes that perform peptide (amide) bond hydrolysis under physiological conditions. Proteases are classified as serine, cysteine, aspartyl, or metallo proteases depending on the mechanism by which they hydrolyze peptide bonds.

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