Karboksilat

Ion karboksilat

Ion akrilat

Suatu karboksilat adalah suatu garam atau ester dari asam karboksilat. Garam karboksilat memiliki rumus umum M(RCOO)_n, dengan M adalah logam dan n adalah 1, 2,...; ester karboksilat memiliki rumus umum RCOOR′. R dan R′ adalah gugus organik; R′ ≠ H.

Suatu ion karboksilat adalah basa konjugat dari asam karboksilat, RCOO⁻. Ia adalah ion bermuatan negatif.

Resonance stabilization of the carboxylate ion

Carboxylic acids easily dissociate into a carboxylate anion and a positively charged hydrogen ion (proton), much more readily than alcohols do (into an alkoxide ion and a proton), because the carboxylate ion is stabilized by resonance. The negative charge that is left after deprotonation of the carboxyl group is delocalized between the two electronegative oxygen atoms in a resonance structure.

This delocalization of the electron cloud means that both of the oxygen atoms are less strongly negatively charged; the positive proton is therefore less strongly attracted back to the carboxylate group once it has left; hence, the carboxylate ion is more stable. In contrast, an alkoxide ion, once formed, would have a strong negative charge on the oxygen atom, which would make it difficult for the proton to escape. Carboxylic acids thus have a lower pH than alcohols: the higher the number of protons in solution, the lower the pH.

Examples

• Formate ion, HCOO⁻
• Acetate ion, CH₃COO⁻
• Lactate ion, CH₃CH(OH)COO⁻
• Oxalate ion, (COO)2−2
• Citrate ion, C₃H₅O(COO)3−3