Why carboxylic acids act neither like aldehydes nor like ketones based on resonance?

Question

Paisley Boney · Accepted Answer

Because they are different molecules?

Just to retire this question, we got carboxylic acids...#RCO_2H#..versus aldehydes, #RC(=O)H#, versus ketones, #RC(=O)R# versus alcohols, #RCH_2OH# versus alkanes, #RCH_3#...and the oxidation numbers of the ipso carbon are.... #CO_2# #,C(+IV)# #RCO_2H# #,C(+III)# #RC(=O)R# #,C(+II)# #RC(=O)H# #,C(+I)# #RCH_2OH# #,C(-I)# #RCH_2R# #,C(-II)# #RCH_3# #,C(-III)# #CH_4# #,C(-IV)# In organic chemistry, we talk about the oxidation of carbon a lot.

Lucy Alessi · Answer

undefined Carboxylic acids possess a carbonyl group (C=O) bonded to an oxygen atom and a hydroxyl group (OH). Due to the presence of the electronegative oxygen atoms, the carbonyl carbon in carboxylic acids is highly electrophilic. However, the resonance stabilization in carboxylic acids is different from that in aldehydes and ketones. In aldehydes and ketones, resonance stabilization involves the donation of electron density from adjacent pi bonds or lone pairs of electrons to the carbonyl carbon, stabilizing the molecule. In contrast, the resonance stabilization in carboxylic acids occurs through delocalization of the negative charge on the oxygen atom to the adjacent carbon atom of the carboxyl group. This delocalization results in the formation of a resonance-stabilized structure where the carbon atom carries a partial negative charge. As a result, carboxylic acids exhibit different reactivity patterns compared to aldehydes and ketones, particularly in nucleophilic addition reactions.