Formation of Cyclic Hemiacetal 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 cyclic 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. Contributors Prof. Steven Farmer ( Sonoma State University ) Layne A. Morsch - University of Illinois Springfield