Carboxyl group Information & Carboxyl group Links at HealthHaven.com

carboxyl group bonded to an atom or group of atoms symbolized by "R"

3D model of carboxyl group

A carboxyl group is a set of four atoms bonded together and present in carboxylic acids, including amino acids. Usually abbreviated as either CO₂H or COOH, this set of atoms constitutes a functional group. In every carboxyl group the carbon atom is attached to an oxygen atom by a double bond and to a hydroxyl group (OH) by a single bond. In this way a carboxyl group is equivalent to a carbonyl group bonded to a hydroxyl group.

The acidic nature of a carboxyl group arises from its H atom. Specifically, in aqueous solution the H atom can be transferred as H⁺ to H₂O molecules, forming H₃O⁺ and leaving behind a COO^– group. For example, the H atom in the carboxyl group of acetic acid (CH₃COOH) reacts with H₂O to make H₃O⁺ and the acetate ion: CH₃COOH + H₂O → H₃O⁺ + CH₃COO^–.

The drawings on this page show a carboxyl group bonding to an atom, or a groups of atoms, through its own carbon. In these representations, "R" symbolizes the atom or atoms to which bonding occurs. As examples, R = H for HCOOH, formic acid, but R = CH₃ for acetic acid, CH₃COOH.

The COOH group has only a separate fleeting existence when not bonded to a fifth atom. In such cases it is called the carboxyl radical and symbolized as •COOH.^[1] The acid dissociation constant of •COOH has been measured using electron paramagnetic resonance spectrocopy.^[2]

[edit] References

^ Milligan, D. E.; Jacox, M. E. (1971). "Infrared Spectrum and Structure of Intermediates in Reaction of OH with CO". Journal of Chemical Physics 54 (3): 927–942. doi:10.1063/1.1675022.
^ The value is pKa = -0.2 ± 0.1 according to the work of Jeevarajan, A. S.; Carmichael, I.; Fessenden, R. W. (1990). "ESR Measurement of the pKa of Carboxyl Radical and Ab Initio Calculation of the C-13 Hyperfine Constant". Journal of Physical Chemistry 94 (4): 1372–1376. doi:10.1021/j100367a033.

[edit] External links

[0] Milligan, D. E.; Jacox, M. E. (1971). "Infrared Spectrum and Structure of Intermediates in Reaction of OH with CO". Journal of Chemical Physics 54 (3): 927–942. doi:10.1063/1.1675022.

[1] The value is pKa = -0.2 ± 0.1 according to the work of Jeevarajan, A. S.; Carmichael, I.; Fessenden, R. W. (1990). "ESR Measurement of the pKa of Carboxyl Radical and Ab Initio Calculation of the C-13 Hyperfine Constant". Journal of Physical Chemistry 94 (4): 1372–1376. doi:10.1021/j100367a033.

[1]

[2]