Organic Study Guide

Organic Study Guide - 2 OH are cis to each other, the...

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Organic Study Guide CH - 25 Aldotetroses are carbohydrates that contain an aldehyde and posses 4 carbons. Aldotetroses have 2 stereocenters. Recall from chapter 4 that for a molecule with n stereocenters, 2 n possible stereoismers can exist. Use this formula to calculate the maximum number of stereoisomers. Glycogen is a polymer of glucose joined by -1,4- and -1,6-glycosidic bonds. It is the energy-reserve molecule of all animals and is found mostly in the liver and muscle. All carbohydrates do NOT have the general formula C n H 2n O n . Sucrose, a disaccharide of glucopyranose and fructofuranose, is also known as table sugar. In order to be a D monosaccharide, the OH group on the penultimate carbon must point to the right on a Fischer projection. refers to a particular isomer of the cyclic form of a carbohydrate. and are used to describe the relative stereochemistry of the anomeric OH group and the CH 2 OH group at the penultimate carbon. If the OH and CH
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Unformatted text preview: 2 OH are cis to each other, the carbohydrate is . If they are trans to each other, the carbohydrate is . When drawn in a Fisher projection, the penultimate carbon is the last stereocenter (at the bottom) on the sugar. When a sugar cyclizes, the penultimate carbon ends up to the left of the oxygen in the ring. An L-sugar represents the mirror image of its D-counterpart. In other words, D and L represent enantiomers. If in the pair shown only the penultimate carbons differ in configuration, they are diastereomers. Furanoses are 5-membered rings. All hemiacetal or hemiketal forms of carbohydrates will undergo mutarotation over time. Eventually, an equillibrium is established between all species involved in the mutarotation. A sugar will not undergo mutarotation if the anomeric carbon is part of an acetal or ketal group, because these groups are not in equilibrium with their carbonyl forms....
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