CARBOXYLATE ANION

A 'carboxylate anion' is an ion with negative charge
that contains the group -COO⁻. It is the conjugate base of a carboxylic acid.
Carboxylic acids dissociate into a carboxylate ion and a positively-charged hydrogen ion (proton) much more readily than alcohols dissociate (into an alkoxide ion and a proton), because the carboxylate ion is more stable: the negative charge that is left behind when a proton leaves the carboxylate group is 'shared' between the two electronegative oxygen atoms in a resonance structure. This delocalization of the electron cloud means that neither of the oxygen atoms is so strongly negatively charged, and thus less readily attracts the positively-charged proton back to the carboxylate group once it has left. On the other hand, 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. Thus, the carboxylate ion is more stable - this is also why carboxylic acids have a lower pH than alcohols: the higher the number of protons that escape into solution, the lower the pH. ^[1]

Contents

Examples

Discussion

References

Examples

★ formate ion, HCOO⁻

★ acetate ion, CH₃COO⁻
See for a bigger list.

Discussion

See carboxylic acid for info.

References

1. Organic Chemistry, Fox, Marye Anne; Whitesell, James K., , , Jones and Bartlett Publishers, 1997, ISBN 0-7637-0178-5