Chapter 22, Problem 32P

Interpretation Introduction

Interpretation:

The structure of lactose sugar based on the given experimental evidences is to be shown.

Concept introduction:

舧 Chair conformations: It is the most stable conformation, which accurately shows the spatial arrangement of atoms.

舧 Equatorial bonds are parallel to the average plane of the ring, while axial bonds are perpendicular to the average plane of the ring.

舧 The conformation having bonds at the equatorial positions are more stable than those with bonds at the axial position.

舧 On flipping the cyclohexane ring, axial bonds become equatorial bonds and equatorial bonds becomes axial bond.

舧 Bulkier group acquires equatorial positions to form stable conformer due to steric factors.

舧 The most stable configuration of aldopyranoses is when the $-{\text{CH}}_{\text{2}}\text{OH}$ group exists in equatorial conformation.

舧 Stereochemistry: The equatorial orientation refers to the spatial arrangement of $-{\text{CH}}_{\text{2}}\text{OH}$ group at $\text{C-2}$ in the same plane, and the axial orientation refers to the spatial arrangement of $-{\text{CH}}_{\text{2}}\text{OH}$ group at $\text{C-2}$ along the axis.

舧 The anomeric effect is lowest for sugars with equatorial orientation, which results in lower energetic state, and consequently this type of orientation confers higher stability.

舧 The anomeric effect is highest for sugars with axial orientation, which results in higher energetic state, and consequently this type of orientation confers lower stability.

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.

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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 Lactose is a disaccharide carbohydrate present in milk (mammary glands) of the mammals. It has a reducing nature and undergoes hydrolysis to yield $\text{D}-\text{galactose and D}-\text{glucose }$.

舧 The aldehyde group of an aldose reacts with three moles of phenylhydrazine to produce phenylosazone at $C-2$ position. Osazones are products of oxidation.

舧 The monosaccharides with five or more carbons atoms form cyclic structures in aqueous solution, and they can form two cyclic stereoisomers from each straight-chain monosaccharide, known as anomers. In aqueous solution, the two anomers and the straight-chain structure of a monosaccharide form an equilibrium mixture through the process of mutarotation.