Carboxylate group

Carboxylate group. R is a hydrogen atom or an organic radical ( alkyl or aryl group ).

In organic chemistry, a carboxylate group or carboxyate group is a deprotonated carboxy group (R-COO ^- ). It is formed during the neutralization of carboxylic acids by alkalis , in that the hydroxide ion takes over a proton from the carboxy group in aqueous solution :

${\displaystyle \mathrm {R{-}COOH\ +\ OH^{-}\longrightarrow \ R{-}COO^{-}\ +\ H_{2}O} }$

In aqueous solutions of carboxylic acids only a small proportion of the dissolved acid molecules release the proton of their carboxy group to a water molecule:

${\displaystyle \mathrm {R{-}COOH\ +\ H_{2}O\longrightarrow \ R{-}COO^{-}\ +\ H_{3}O^{+}} }$

So there are For example, every hundredth acetic acid molecule in diluted vinegar loses its proton, so that only one percent of the carboxy groups are converted into the carboxylate groups of the acetate ions (partial protolysis ). With increasing dilution, the degree of dissociation also increases . This relationship is described by Ostwald's law of dilution .

In the carboxylate group, the negative charge is evenly distributed (delocalized) over the two oxygen atoms due to the mesomerism . The carbon atom is in the sp ² -hybridized state, so that the carboxylate group is axially symmetrical and planar. The three bonds of the carbon atom form bond angles of approximately 120 °.

literature

• Organikum , 16th edition, VEB Deutscher Verlag der Wissenschaften Berlin 1985, ISBN 3-326-00076-6 .
• Peter Sykes: reaction mechanisms - an introduction , 8th edition VCH Weinheim 1982 ISBN 3-527-21090-3 .