Formation of cyclic hemiacetals and acetals

Molecules which have an alcohol and a carbonyl can undergo an intramolecular reaction to form a cyclic hemiacetal.

Intramolecular Hemiacetal formation is common in sugar chemistry. For example, the common sugar glucose exists in the cylcic manner more than 99% of the time in a mixture of aqueous solution.

Carbonyls reacting with diol produce a cyclic acetal.  A common diol used to form cyclic acetals is ethylene glycol.