Electrophilicity is defined as the relative reactivity of an electrophilic reagent.

However, whereas Lewis acidity is measured by relative equilibrium constants, electrophilicity is measured by relative rate constants for reactions of different electrophilic reagents towards a common substrate (usually involving attack at a carbon atom). 

Relative Electrophilicity in Carbonyl and Carboxylic acid derivatives,

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 relative 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 substitutent in the following ways: 

• the effect the substituent has on the electrophilicity of the carbonyl C 
• if the substituent is electron donating, then the electrophilicity is reduced, \ less reactive
• if the substituent is electron withdrawing, the the electrophilicity is increased, \more reactive
• the ability of the substituent to function as a leaving group.

Carbonyls as aldehydes and Ketones Carbon atoms are less electrophilic than Acid Chloride and acid anhydrides but more electrophilic than thioester, ester, acid amide and Carboxylates.