Chapter 22, Problem 29P

Interpretation Introduction

Interpretation:

The series of chemical reactions that can be used for the production of D-mannose from D-glucose utilizing the fact that aldonic acids are specifically epimerized at 2^nd carbon atom on treatment with pyridine (heat) is to shown.

Concept introduction:

舧 Formation of isomers is called isomerization. Monosaccharides undergo a series of keto-enol tautomerizations and enolizations and to produce different isomeric forms. In order to preserve the stereochemical nature of the compounds, the formation of such isomeric forms needs to be prevented.

舧 Stereochemistry: A carbon atom is attached to four distinct groups is said to be a stereogenic or chirality center of that molecule. A stereocenter is that point in a molecule where any two groups exchange their positions to form stereoisomers.

舧 The pair of diastereomers that shows different configuration at the chirality center are called epimers. The aldohexoses, $\text{D}-\text{Mannose and D}-\text{Glucose}$, are epimers.

舧 A carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen-oxygen atom ratio of 2:1

舧 ${\text{HNO}}_{\text{3}}$ is an oxidizing agent.

舧 Carbohydrates are oxidized by ${\text{HNO}}_{\text{3}}$ to give aldaric acid as a product.

舧 Aldaric acids are carbohydrates having two carboxylic acids. They are formed due to oxidation reaction of aldoses with dilute ${\text{HNO}}_{\text{3}}$ and their general reaction can be represented as:

舧 Monosaccharides containing six carbon atoms and an aldehyde group are called aldohexoses.

舧 Alditols are compounds produced from aldoses or ketoses on reduction with certain reagents such as sodium borohydride (${\text{NaBH}}_{\text{4}}$) and hydrogen along with a catalyst.

舧 Compounds formed by the reaction of reducing sugars with excess of phenyl hydrazine are called osazones. Osazones are products of oxidation and are produced by all reducing sugars.

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舧 Fischer projection is a way of representing the structural formulae of compounds through cross formulation of their open chain structures.

舧 Bromine water is an effective reagent that selectively oxidizes the $-\text{CHO}$ group to $-\text{COOH}$ moiety, and thereby, converts an aldose into aldonic acid.

舧 While dissolved in aqueous bases such as pyridine, monosaccharides undergo complex isomerization as they form different enols and keto-enols. Aldonic acids form epimers (usually at the ${\text{C}}_{\text{2}}$ atom) when they react with the base, pyridine.