ACS Organic Chemistry Exam Questions & Complete Solutions 2024/2025

What is the general formula for a carbohydrate? - Correct Answer Cx(H2O)y How do you determine the number of stereoisomers for a given carbohydrate? - Correct Answer 2^n where n= number of stereocenters Distinguish between the D and L designations for carbohydrates. - Correct Answer In the L form the hydroxy group is on the bottom left closest to the CH2OH group in the frame of a Fischer projection In the D form the OH is on the bottom right What are anomers? - Correct Answer Diastereomers formed by the cyclization of carbohydrates (*note they have different configurations at the new stereocenter-this is what makes them diastereomers) Distinguish between alpha and beta anomers. - Correct Answer beta anomers have the OH belonging to the hemiacetal carbon equatorial alpha anomers have the OH belonging to the hemiacetal carbon axial What is the definition of mutarotation? - Correct Answer the process for which alpha and beta anomers come to equilibrium (aqueous) in a specific ratio. It is the same ratio is observed when you start with the alpha anomer in water versus the beta anomer in water What agent is most often used for complete oxidation of a carbohydrate? - Correct Answer HNO3 What kind of agents are used for selective or partial oxidation of carbohydrates? - Correct Answer most commonly Br or some other MILD oxidative agent What are reducing sugars? - Correct Answer Carbohydrates that yield positive results of the oxidative tests, because in being oxidized they reduce the metal ion (or other reducing agent) C