Carboxylate anion
Encyclopedia
A carboxylate is a salt or ester
of a carboxylic acid
.
Carboxylate salts have the general formula M(RCOO)n, where M is a metal and n is 1,2,...; carboxylate esters have the general formula RCOOR'. R and R' are organic groups; R'≠H.
A carboxylate ion is the conjugate base of a carboxylic acid, RCOO−. It is an ion
with negative charge.
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 either of the oxygen atoms is less strongly negatively charged; the positively charged proton is therefore less strongly attracted back to the carboxylate group once it has left. 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. Thus, the carboxylate ion is more stable and carboxylic acids have a lower pH
than alcohols: the higher the number of protons in solution, the lower the pH.
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
of a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
.
Carboxylate salts have the general formula M(RCOO)n, where M is a metal and n is 1,2,...; carboxylate esters have the general formula RCOOR'. R and R' are organic groups; R'≠H.
A carboxylate ion is the conjugate base of a carboxylic acid, RCOO−. It is an ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
with negative charge.
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 alkoxideAlkoxide
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands...
ion and a proton), because the carboxylate ion is stabilized by resonance
Resonance (chemistry)
In chemistry, resonance or mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula...
. The negative charge that is left after deprotonation
Deprotonation
Deprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...
of the carboxyl group is delocalized between the two electronegative oxygen atoms in a resonance structure.
This delocalization of the electron cloud means that either of the oxygen atoms is less strongly negatively charged; the positively charged proton is therefore less strongly attracted back to the carboxylate group once it has left. 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. Thus, the carboxylate ion is more stable and carboxylic acids have a lower pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
than alcohols: the higher the number of protons in solution, the lower the pH.