. Functional derivatives of carboxylic acids Compounds such as acid chlorides, amides, esters etc., are called carboxylic acid derivatives because they differ from a carboxylic acid only in the nature of the group or atom that has replaced the -OH group of carboxylic acid. Group replacing - OH Name Structure Example –Cl Acid chloride R Cl Cl Acetyl chloride –NH Acid amide R NH NH Acetamide –OR' ester R OR' OCH Methyl acetate –OOCR Acid anhydride R R R Acetic anhydride XII U12-Carbonyl XII U12-Carbonyl - - - - Relative reactivity of Acid derivatives The reactivity of the acid derivatives follows the order R C Cl > R C O C R > R C OR' > R C NH The above order of reactivity can be explained in terms of i) Basicity of the leaving group ii) Resonance effect (i) Basicity of the leaving group Weaker bases are good leaving groups. Hence acyl derivatives with weaker bases as leaving groups (L) can easily rupture the bond and are more reactive.
The correct order of the basicity of the leaving group is H N : > : OR > RCOO : > : Cl Hence the reverse is the order of reactivity. (ii) Resonance effect Lesser the electronegativity of the group, greater would be the resonance stabilization as shown below. This effect makes the molecule more stable and reduces the reactivity of the acyl compound. The order of electronegativity of the leaving groups follows the order – Cl > - OCOR > - OR > - NH Hence the order of reactivity of the acid derivatives with nucleophilic reagent follows the order acid halide > acid anhydride > esters > acid amides .
. Nomenclature Compound (common name, Structural formula, IUPAC Name) IUPAC Name Prefix with position number Root used Primary suffix Secondary Suffix Acetyl chloride Cl Ethanoylchloride – eth ane / oyl chloride Propionyl chloride C H Cl Propanoylchloride – prop ane / oyl chloride Benzoyl chloride C H Cl Benzoylchloride – Benz ane