Return to Contents  Chapter  19: Carboxylic Acids  Ch 19 contents

Carboxylic Acids

Nomenclature:
Functional group suffix = -oic acid (review)
If the acid is substituted onto a ring the suffix -carboxylic acid is used.
 

 
IUPAC name: methanoic acid ethanoic acid  propanedioic acid butanedioic acid
Trivial name: formic acid acetic acid  malonic acid succinic acid

The anion dervived by deprotonation of a carboxylic acids is the carboxylate.

Physical Properties:

Structure: Acidity:
Carboxylic Acid Structure pKa
Ethanoic acid CH3CO2H 4.7
Propanoic acid CH3CH2CO2H 4.9
Fluoroethanoic acid CH2FCO2H 2.6
Chloroethanoic acid CH2ClCO2H 2.9
Dichloroethanoic acid CHCl2CO2H 1.3
Trichloroethanoic acid CCl3CO2H 0.9
Nitroethanoic acid O2NCH2CO2H 1.7

Reactivity:
 

electrostatic potential of acetic acid The image shows the electrostatic potential for acetic acid (ethanoic acid). 
The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density. 
  • There is low electron density (blue) on H atom of the -CO2H group alcohol, i.e. H+ character. 
  • The H atom of the RCO2H is acidic (pKa ~ 5).
  • The most important reactions of carboxylic acids converts them into carboxylic acid derivatives such as acyl halides, esters and amides via nucleophilic acyl substitution reactions.
electrostatic potential of acetate ion The image shows the electrostatic potential for the acetate ion (ethanoate ion) 
The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density. 
  • There is high electron density (red) on both O atoms of the -CO2- group alcohol, i.e. resonance and basic or nucleophilic behaviour

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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary