The percent of (R)-glyceraldehyde present in the given mixture has to be calculated. Concept introduction: The pair of Enantiomers has different configurations. Pair of enantiomers has different optical activity, which means if one will show levorotatory then the other will show dextrorotatory. The direction and magnitude of rotation of plane-polarized light by an optically compound is measured by using polarimeter . This rotation of polarized light is specific for a compound at specified temperature and wavelength, so it is called as Specific rotation of that compound. The specific rotation of enantiomers has equal magnitudes and opposite signs. Racemic mixture (equal amounts of enantiomers) of a compound has zero specific rotation. If the mixture contain unequal amount of enantiomers of a compound, then the amount of excess of enantiomer is called enantiomeric excess or optical purity. It is calculated by, enantiomeric excess = observed specific rotation specific rotation of the pure enantiomer ×100%

Question

The specific rotation of α-d-galactose is 150.7 and that of β-d-galactose is 52.8. When an aqueous mixture that was initially 70% α-d-galactose and 30%β-d-galactose reaches equilibrium, the specific rotation is 80.2. What is the percentage of α-d-galactose and β-d galactose at equilibrium?

Answer 1

Question

Chapter 4, Problem 83P

Interpretation Introduction

Interpretation:

The percent of (R)-glyceraldehyde present in the given mixture has to be calculated.

Concept introduction:

The pair of Enantiomers has different configurations.

Pair of enantiomers has different optical activity, which means if one will show levorotatory then the other will show dextrorotatory.

The direction and magnitude of rotation of plane-polarized light by an optically compound is measured by using polarimeter.

This rotation of polarized light is specific for a compound at specified temperature and wavelength, so it is called as Specific rotation of that compound.

The specific rotation of enantiomers has equal magnitudes and opposite signs.

Racemic mixture (equal amounts of enantiomers) of a compound has zero specific rotation.

If the mixture contain unequal amount of enantiomers of a compound, then the amount of excess of enantiomer is called enantiomeric excess or optical purity. It is calculated by,

enantiomeric excess =observed specific rotationspecific rotation of the pure enantiomer×100%

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