Chapter 20: Carboxylic Acid Derivatives. Nucleophilic Acyl Substitution

Structure of Carboxylic Acid Derivatives

• The carbonyl group consists of an O atom bonded to a C atom via a double bond in a planar, sp² hybridization model similar to that of a ketone or an alkene.
• The heteroatom group is connected to this C=O unit via a s bond.
• To see these features, compare the CHIME images to the below.
• CHIME images of the other carboxylic acid derivatives can be found on the previous page.

• The resonance interaction of the carbonyl C=O with the lone pair of the adjacent heteroatom (structure III) has important implications on the reactivity

It also has implications for structure... Look at the CHIME image of the amide to the right.  What do you notice about the geometry at the N atom ?  Amines and ammonia are usually pyramidal (want to see ?) The planar sp2 N system allows the N lone pair to align with the C=O p system (see image below, with the other bonds omitted for clarity) The resonance interaction in the amide results in the C-N bond having some double bond character (shorter, restricted rotation)

amide