Chapter 22, Problem 35P

Interpretation Introduction

Interpretation:

The distinguishing tests for the pair of given compounds are to be determined.

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.

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Tollen’s (${\text{[Ag}}^{\text{+}}{{\text{(NH}}_{\text{3}}\text{)}}_{\text{2}}{\text{OH}}^{-}\text{]}$)/Benedict’s (alkaline solution with cupric citrate complex ion) test is a qualitative test to distinguish aldehydes from ketones. These reagents are used to determine the presence of carboxyl groups; both aromatic and non-aromatic aldehydes and $\alpha -$ hydroxy ketones. All reducing sugars (having hemiacetal group) give positive Tollen’s / Benedict’s test whereas non-reducing sugars (having acetal groups) do not. However, reactions with these reagents are not that easy because these tests require alkaline solutions, which can induce complex chemical alterations in the sugars.

舧 Compounds that have plane of symmetry tend to form meso compounds. A meso form arises when the two stereoisomers produce superimposable (achiral) images, and hence, compounds having meso are optically inactive. Chiral (or non-superimposable) molecules are optically active.

舧 ${\text{HIO}}_{\text{4}}$ is known as the periodic acid. It is used for oxidative cleavage of compounds having hydroxyl groups on adjacent atoms to produce respective aldehydes, ketones and acids.