ACS Organic Chemistry Exam.

ACS Organic Chemistry Exam


What is the general formula for a carbohydrate? - (CORRECT ANSWER)-Cx(H2O)y
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How do you determine the number of stereoisomers for a given carbohydrate? -
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(CORRECT ANSWER)-2^n where n= number of stereocenters
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Distinguish between the D and L designations for carbohydrates. - (CORRECT ANSWER)-In
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the L form the hydroxy group is on the bottom left closest to the CH2OH group in the
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frame of a Fischer projection
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In the D form the OH is on the bottom right
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What are anomers? - (CORRECT ANSWER)-Diastereomers formed by the cyclization of
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carbohydrates (*note they have different configurations at the new stereocenter-this is
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what makes them diastereomers)
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Distinguish between alpha and beta anomers. - (CORRECT ANSWER)-beta anomers have
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the OH belonging to the hemiacetal carbon equatorial
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alpha anomers have the OH belonging to the hemiacetal carbon axial
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What is the definition of mutarotation? - (CORRECT ANSWER)-the process for which alpha
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and beta anomers come to equilibrium (aqueous) in a specific ratio. It is the same ratio is
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observed when you start with the alpha anomer in water versus the beta anomer in water
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What agent is most often used for complete oxidation of a carbohydrate? - (CORRECT
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ANSWER)-HNO3
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, What kind of agents are used for selective or partial oxidation of carbohydrates? -
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(CORRECT ANSWER)-most commonly Br or some other MILD oxidative agent
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What are reducing sugars? - (CORRECT ANSWER)-Carbohydrates that yield positive
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results of the oxidative tests, because in being oxidized they reduce the metal ion (or
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other reducing agent)
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Carbohydrates undergo reactions similar to which functional group? - (CORRECT
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ANSWER)-OH (hemiacetals and acetals)
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How does the Tollen's test work? - (CORRECT ANSWER)-Carbohydrate is oxidized by Ag+
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and positive result shows a silvery mirror as Ag+ is reduced to metallic (elemental) silver
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How do the Benedict's and Fehling's tests work? - (CORRECT ANSWER)-Both employ a
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solution of aqueous Cu2+ in base. When reduced it forms Cu2O which is a red ppt.
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What is a glycoside? - (CORRECT ANSWER)-a sugar bonded to another oxygen containing
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functional group to make the carbohydrate a full acetal rather than a hemiacetal
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What does a glycosidic bond consist of? - (CORRECT ANSWER)-A glycosidic bond is
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between C4 (the acetal carbon) and another oxygen atom
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What is the difference between an alpha and a beta glycosidic bond? - (CORRECT
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ANSWER)-the alpha bond is axial
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the equatorial bond is equatorial
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What is a nucleophile? - (CORRECT ANSWER)-An electron rich species than seeks an
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electron poor site
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