Compounds having the structure R2C(OR')2 (R'H) and thus diethers of geminal diols. Originally, the term was confined to derivatives of aldehydes (one R = H), but it now applies equally to derivatives of ketones (neither R = H). Mixed acetals have different R' groups.
See also: acetonides, ketals, acylals, hemiacetals
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1310 (