Nomenclature:

Acyl Chlorides Functional group suffix = oyl chloride (review)
Anhydrides Functional group suffix = alkanoic anhydride (review)
Esters Functional group suffix = alkyl -oate (review)  Functional group prefix = alkoxycarbonyl-  or   carbalkoxy- Cyclic esters are called lactones
Carboxylic Acids Functional group suffix = -oic acid (review)  Functional group prefix = carboxy-
Amides Functional group suffix = amide (review)  Functional group prefix = carbamoyl- Cyclic amides are called lactams
Nitriles Functional group suffix = nitrile or -onitrile (review)  Functional group prefix = cyano-

• 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.
• Nitriles consists of a N atom bonded to a C atom via a triple bond in a linear, sp hybridization model similar to that of an alkyne.
• The resonance interaction of the carbonyl 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 amide in the table above....  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 to the right, 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)

Reactivity:

Carboxylic acid derivatives react tend to react via Nucleophilic Acyl substitution where the group on the acyl unit, R-C=O undergoes substitution:

The observed reactivity order is shown below:

It is useful to view the carboxylic acid derivatives as an acyl group, R-C=O,  with a different substituent attached.  The important features of the carboxylic acid derivatives that influence their reactivity are governed by this substituent in the following ways:  the effect the substituent has on the electrophilicity of the carbonyl C (review substituent effects ?) if the substituent is electron donating, then the electrophilicity is reduced, \ less reactive if the substituent is electron withdrawing, the electrophilicity is increased, \ more reactive the ability of the substituent to function as a leaving group.

I  and II are similar to those of aldehydes and ketones, but there is also a third possibility III where a lone pair on the heteroatom Z is able to donate electrons to the adjacent positive center. The stronger this electron donation from Z the less positive the carbonyl C and the less electrophilic the carbonyl group.  The ability of Z to donate electrons is linked to its electronegativity...the more electronegative Z is, the less the stabilizing effect.

Use the following series of electrostatic potential  maps to look at the electrophilicity of the carbonyl C in a example of each carboxylic acid derivative. Note how the blue colour gradually reduces in intensity down the series.

	The image shows the electrostatic potential for ethanoyl chloride.  The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density.
	The image shows the electrostatic potential for ethanoic anhydride.  The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density.
	The image shows the electrostatic potential for methyl ethanoate.  The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density.
	The image shows the electrostatic potential for ethanamide.  The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density.
	The image shows the electrostatic potential for acetonitrile.  The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density.