Chapter 22, Problem 31P

Interpretation Introduction

Interpretation:

The structure of the anhydrous sugar (${\text{C}}_6{\text{H}}_{10}{\text{O}}_5$) and the series of chemical reactions required to produce this anhydrous sugar is to be represented. Moreover, the reason for the requirement of drastic conditions for the production of anhydro sugar from D-glucose also needs to be explained.

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 Sugars that have moisture content below 0.5% are said to be anhydrous sugars. They are usually high purity crystalline sugars obtained from $\text{D}-\text{Glucose}$ and its derivatives. Anhydrous sugars may be reducing or nonreducing sugars.

舧 Altrose is an aldohexose sugar with the chemical formula ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}$ >, produced artificially. It is an epimer of mannose at $C-3$ atom.

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 The anhydrous sugar is produced when the axial $-{\text{CH}}_{\text{2}}\text{OH}$ group reacts with C1 atom to produce a cyclic acetal.

舧 Anhydrous sugar is an acetal, it is a nonreducing sugar, and therefore it is called anhydrous non-reducing sugar.