BIOC 2580 Lecture Notes - Lecture 4: Hemiacetal, Stereoisomerism, Aldose
21 Oct 2016
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A sugar with n chiral centers have 2^n stereoisomers. Half of these stereoisomers are _____________ and the other half are _______________ Every time a c atom is added, the number of isomers doubles! **the original carbonyl c becomes chiral upon formation of hemiacetals and hemiketals. Sugars = alcohol + aldehyde or ketone functional groups. For sugars, hemiacetal/hemiketal formation is intramolecular (in the same molecule) Oh gp at c5 reacts with carbonyl c of aldehyde gp to form a stable 6-membered ring. Renders c1 asymmetric, giving rise to 2 stereoisomers alpha and beta. These isomeric form that differ only in configuration around hemiacetal/hemiketal c = anomers. Anomers = isomeric form that differ only in their configuration around the hemiacetal/hemiketal c. Anomeric carbon = only c atom attached to 2 oxygens. It is electrophilic and position where most reactions involving ring forms of sugars take place. Electrophilic carbonyl c atom reacts with the nucleophilic o of and oh group.
