Which one of the following does NOT contain COOH group?

Carboxylic acids are organic compounds defined by the presence of one or more carboxyl groups (-COOH) [1]. Citric acid is a tricarboxylic acid containing three carboxyl groups [1]. Lactic acid, also known as 2-hydroxypropanoic acid, contains one carboxyl group [3]. Tartaric acid is classified as a dicarboxylic acid, meaning it possesses two carboxyl functional groups within its molecular structure. In contrast, Ascorbic acid (Vitamin C) has the molecular formula C6H8O6 and does not contain a -COOH group. Instead, its acidity arises from the presence of enediol hydroxyl groups and a lactone ring structure, which allows it to act as an antioxidant rather than a traditional carboxylic acid [1]. Therefore, among the given options, only ascorbic acid lacks the carboxyl functional group.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC9654595/
2. [2] https://www.sciencedirect.com/topics/medicine-and-dentistry/carboxyl-group
3. [3] https://en.wikipedia.org/wiki/List_of_carboxylic_acids