CHEM 22200 Lecture 2: Handout 2(15)

• School: University of Chicago
• Department: Chemistry
• Course: CHEM 22200
• Professor: Joseph Piccirilli

Document Summary

H (97% at equilibrium) simple aldehydes form hemiacetals in alcohol; just as they form hydrates in water. Five and six-membered cyclic hemiacetals form spontaneously from the corresponding hydroxy aldehydes, and most are stable isolable compounds. 94% at equilibrium) cyclic hemiacetal entropically favored relative to intermolecular case. H (hemiacetal) a (+) glucopyranose cyclic form of glucose most simple sugars exist primarily in a cyclic hemiacetal form (even in water; again it"s formation is entropically favored relative to intermolecular cases. Addition of alcohols; formation of hemiacetals and acetals. Mechanism of acid catalyzed hemiketal and ketal formation hemiacetal acetal. Keq<1 hemiacetal basic conditions not used to make hemiketals or hemiacetals because equillibrium favors carbonyl. Formation of acetals catalyzed by acids or base catalyzed by acids. R" acetal drive equilibrium to right by addition of molecular sieves that soak up water. + h2o stable in basic and neutral solution. All steps in the formation of an acetal from an aldehyde are reversible.