water-soluble organic compound that is necessary for carbohydrate metabolism in both plants and animals. It carries out these functions in its active form, as a component of the coenzyme thiamin pyrophosphate. Thiamin deficiency results in beriberi, a disease characterized by multiple neuritis (lesions of nerves), general debility, and heart failure.

In 1926 thiamin was the first vitamin to be isolated in pure form. Its structure was fully elucidated and the vitamin synthesized in 1936. The chemical structure is as follows: