Carboxyl group is a group composed of carbonyl group and hydroxyl group. It is the functional group of carboxylic acid, and is carboxyl COOH.
Exactly speaking, one hydrogen atom shares two oxygen atoms. Because C forms a large π bond with two oxygen atoms, the effect of two O on H is equivalent.
The univalent group consisting of carbonyl group and hydroxyl group is called carboxyl group. The nature of carboxyl group is not the simple addition of carbonyl group and hydroxyl group. For example, the carbonyl group in the carboxyl group becomes very inactive under the influence of hydroxyl group, and does not interact with HCN and NaHSO three etc. Nucleophile Addition reaction occurs, and its hydroxyl is easier to dissociate than the alcohol hydroxyl, showing weak acidity. In the anions of carboxylates, bond averaging occurs due to the delocalization of electrons. Therefore, its two carbon oxygen bonds are actually identical. In addition, due to the special structure of carboxyl group, it also has the property of aldehyde group (- CHO).
Use new system Copper hydroxide Distinguish aldehyde group from carboxyl group. Phenomenon: the blue flocculent precipitation in the carboxylic acid disappears and turns into a blue solution, which does not change when heated. The reaction principle is: acid-base neutralization Remove the C on the carboxyl group. The first C on the molecule becomes alpha carbon. The carboxyl and amino groups connected to alpha carbon are called alpha carboxyl and alpha- amino , similarly, there is α hydrogen 
