Carbonyl Addition - Loss of carbonyl oxygen

Cyclic acetal formation

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Cyclic acetals are more stable towards hydrolysis than acyclic ones, they are also much easier to make. Cyclic acetals are readily formed by the reaction of two molecules, a ketone and a diol. The reaction produces two products, the acetal plus water, so the usually unfavourable entropy of acetal formation is not a factor. Formation is also kinetically favoured because the intramolecular ring-closing reaction is fast.