Figure 8.4. IUPAC and Common Names of Dicarboxylic AcidsPHYSICAL PROPERTIES
Many of the physical properties of carboxylic acids are similar to those of aldehydes and ketones
because they both contain carbonyl groups. However, the additional hydroxyl group permits
carboxylic acids to hydrogen bond and provides another acidic hydrogen that can participate in
reactions.
Hydrogen Bonding
Carboxylic acids are polar because they contain a carbonyl group and can also form hydrogen bonds
because they contain a hydrogen bonded to a very electronegative atom (in this case, the hydroxyl
oxygen). Carboxylic acids display particularly strong intermolecular attractions because both the
hydroxyl oxygen and carbonyl oxygen can participate in hydrogen bonding. As a result, carboxylic
acids tend to form dimers: pairs of molecules connected by two hydrogen bonds. Multiple hydrogen
bonds elevate the boiling and melting points of carboxylic acids past those of corresponding
alcohols. Boiling points also increase with increasing molecular weight.
KEY CONCEPT
Carboxylic acids are polar and can form hydrogen bonds. Their acidity is due to resonance
stabilization and can be enhanced by the addition of electronegative groups or a greater
ability to delocalize charge.