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🥼organic chemistry review

α-Hydroxy Acid

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

An α-hydroxy acid is an organic compound that contains a hydroxyl (-OH) group attached to the carbon atom adjacent to the carboxyl (-COOH) group. These compounds are important in various chemical reactions, including the formation of cyanohydrins in the context of nucleophilic addition of HCN.

5 Must Know Facts For Your Next Test

  1. α-Hydroxy acids are characterized by the presence of a hydroxyl group on the carbon atom adjacent to the carboxyl group, giving them the general formula R-CH(OH)-COOH.
  2. These compounds are important in the formation of cyanohydrins, which are produced through the nucleophilic addition of HCN to carbonyl groups.
  3. Cyanohydrins are useful intermediates in organic synthesis, as they can be further transformed into a variety of other functional groups.
  4. The presence of the hydroxyl group in α-hydroxy acids can influence their reactivity, solubility, and ability to form hydrogen bonds, which are important in various chemical processes.
  5. Many naturally occurring α-hydroxy acids, such as lactic acid and glycolic acid, play important roles in biological systems and have various applications in the cosmetic and pharmaceutical industries.

Review Questions

  • Explain the structural features of an α-hydroxy acid and how they contribute to the formation of cyanohydrins.
    • An α-hydroxy acid is characterized by the presence of a hydroxyl (-OH) group attached to the carbon atom adjacent to the carboxyl (-COOH) group. This structural feature allows the hydroxyl group to participate in the nucleophilic addition of hydrogen cyanide (HCN) to the carbonyl carbon, resulting in the formation of a cyanohydrin. The hydroxyl group acts as a nucleophile, attacking the electrophilic carbonyl carbon and facilitating the addition of the cyanide group, which is also a nucleophile. The resulting cyanohydrin compound contains a new carbon-carbon bond and a hydroxyl group, making it a useful intermediate in organic synthesis.
  • Describe the role of α-hydroxy acids in the context of the nucleophilic addition of HCN and the formation of cyanohydrins.
    • In the context of the nucleophilic addition of HCN, α-hydroxy acids play a crucial role in the formation of cyanohydrins. The hydroxyl group on the α-carbon of the α-hydroxy acid acts as a nucleophile, attacking the electrophilic carbonyl carbon of a carbonyl-containing compound. This nucleophilic addition allows the cyanide group from HCN to be incorporated into the molecule, creating a new carbon-carbon bond and a hydroxyl group. The resulting cyanohydrin product is a valuable intermediate in organic synthesis, as it can be further transformed into a variety of other functional groups.
  • Analyze the importance of the structural features of α-hydroxy acids in their reactivity and the implications for the nucleophilic addition of HCN and cyanohydrin formation.
    • The structural features of α-hydroxy acids, specifically the presence of the hydroxyl group on the carbon adjacent to the carboxyl group, are crucial in their reactivity and the formation of cyanohydrins. The hydroxyl group acts as a nucleophile, attacking the electrophilic carbonyl carbon and facilitating the addition of the cyanide group from HCN. This nucleophilic addition leads to the formation of a new carbon-carbon bond and a hydroxyl group, resulting in a cyanohydrin product. The ability of α-hydroxy acids to participate in this reaction is a consequence of their unique structural characteristics, which allow for the hydroxyl group to be positioned in a favorable orientation for the nucleophilic addition. Understanding the importance of these structural features is essential in comprehending the role of α-hydroxy acids in the context of nucleophilic addition of HCN and cyanohydrin formation.