Carboxyl Group

Definition

The carboxyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl (OH) group. It is a key structural feature found in many organic compounds, particularly carboxylic acids, aldehydes, ketones, and esters.

5 Must Know Facts For Your Next Test

1. The carboxyl group is polar due to the electronegativity difference between the carbon and oxygen atoms, making it a good hydrogen-bond acceptor.
2. Carboxylic acids, which contain a carboxyl group, are weakly acidic compounds that can donate a proton (H+) to a base, forming a carboxylate ion.
3. Esters, which are formed by the reaction of a carboxylic acid and an alcohol, have a characteristic C-O-C linkage that is less polar than the C=O bond in the carboxyl group.
4. Aldehydes and ketones, which also contain a carbonyl group (C=O), can be distinguished from carboxylic acids by the absence of the hydroxyl (OH) group in the carboxyl group.
5. The carboxyl group plays a crucial role in the structure and reactivity of many biomolecules, such as amino acids, fatty acids, and various metabolites.

Review Questions

• Explain the polarity and hydrogen-bonding properties of the carboxyl group and how they influence the behavior of carboxylic acids.
  • The carboxyl group is polar due to the electronegativity difference between the carbon and oxygen atoms. This polarity allows the carboxyl group to act as a good hydrogen-bond acceptor. In carboxylic acids, the hydrogen atom of the hydroxyl group in the carboxyl group can be donated to a base, forming a carboxylate ion. This ability to donate protons and form hydrogen bonds contributes to the weak acidity of carboxylic acids and their solubility in polar solvents, such as water.
• Describe the structural differences between carboxylic acids, aldehydes, and ketones, and how the presence or absence of the carboxyl group affects their reactivity.
  • Carboxylic acids contain a carboxyl group (C=O-OH), while aldehydes and ketones contain a carbonyl group (C=O) but lack the hydroxyl group. This structural difference has important implications for their reactivity. Carboxylic acids can participate in acid-base reactions and form salts, esters, and other derivatives due to the presence of the acidic hydrogen in the hydroxyl group. In contrast, aldehydes and ketones are more susceptible to nucleophilic addition reactions at the carbonyl carbon, as they lack the acidic hydrogen.
• Explain the role of the carboxyl group in the formation of esters and the significance of this reaction in organic chemistry and biochemistry.
  • The carboxyl group plays a crucial role in the formation of esters, which are important compounds in organic chemistry and biochemistry. Esters are formed by the reaction of a carboxylic acid and an alcohol, with the elimination of water. The carboxyl group provides the carbonyl carbon that is attacked by the nucleophilic alcohol, leading to the characteristic C-O-C linkage in esters. Esters have diverse applications, from the synthesis of fragrances and flavorings to the formation of important biomolecules, such as lipids and various metabolites. The reversible nature of ester formation and hydrolysis also makes esters important in many biological processes, such as energy storage and transport.

Related terms

Carboxylic Acid:

An organic compound containing a carboxyl group, typically with the general formula R-COOH, where R represents an alkyl or aryl group.

Ester: A compound formed by the reaction of a carboxylic acid and an alcohol, with the elimination of water, resulting in the characteristic R-COO-R' structure.

Nucleophilic Acyl Substitution: A type of reaction where a nucleophile attacks the carbonyl carbon of a carboxylic acid derivative, such as an ester or acyl chloride, leading to the formation of a new compound.