Enantiomeric Excess - Online Tutor, Practice Problems & Exam Prep

The α- and β-anomer of D-galactose can interconvert via mutarotation. 

When the anomers are separately dissolved in water, their individual specific rotation, [α], gradually changes until it reaches +80.2°. Why does this happen?

Which of the following is a possible method for separating the enantiomers of 2-benzyl-3-methylbutanoic acid?

A solution of an unknown compound has a concentration of 5.0 g/ml and an observed rotation of -25° in a 3.0 dm polarimeter tube. Determine its specific rotation.

60 g of compound A was dissolved to 20 mL and placed in a 1.0-cm polarimeter cell. Calculate the specific rotation of compound A if the observed rotation of the solution is +15.3°.

An unknown compound's (+)-isomer has a specific rotation of +148^o. Calculate its observed rotation if a mixture contains 60.0 % (-)-isomer and 40.0 % (+)-isomer.

7.0 g/mL of a substance has an observed rotation of +120°. In a polarimeter tube that is 10 cm long, calculate its specific rotation.

A mixture consists of 20% of (+)-pentan-2-ol and 80% of (−)-pentan-2-ol. Determine the specific rotation of the mixture if the specific rotation of pure (−)-pentan-2-ol is 13.0º.

A solution of a chiral molecule gives a rotation about 179.9º. Propose a way to tell if the rotation is +180º or −180º.

A solution was prepared by dissolving 1.8 g of (−)-glyceraldehyde in 9.00 mL of water. The solution was placed in a 100-mm cell and the rotation was then measured at 25℃ using the sodium D line. If the rotation observed was −1.74º, calculate the specific rotation of (−)-glyceraldehyde.

Consider a theoretical reaction that is designed to produce one enantiomer to the exclusion of the other. If difference in activation energy between enantiomer A and enantiomer B is 3.5 kcal/mol and enantiomer B has the lower activation energy, at what temperature would you produce enantiomer B in 99% ee?

Addition of a chiral molecule to the catalytic reduction of pentan-2-one produces a slightly optically active product. Determine the percentage of (+)-pentan-2-ol and (−)-pentan-2-ol formed in the reaction if the specific rotation of the product is +0.54º. (The rotation of pure (−)-pentan-2-ol at the same condition is 13.0º)

A. (+)-pentan-2-ol =  0.54 % and (−)-pentan-2-ol = 99.46 %

B. (+)-pentan-2-ol =  47.9 % and (−)-pentan-2-ol = 52.1 %

C. (+)-pentan-2-ol =  52.1 % and (−)-pentan-2-ol = 47.9 %

D. (+)-pentan-2-ol =  95.85 % and (−)-pentan-2-ol = 4.15 %

An optically pure alkyl halide (R-enantiomer) is heated with water and forms an alcohol. Three times more of the S-enantiomer of the alcohol is produced compared to the R-enantiomer. Determine the enantiomeric excess and the observed rotation of the product mixture. (S-enantiomer of the alcohol [α] = +16.3°)

The following racemic mixture of enantiomeric carboxylic acids was synthesized in the laboratory. Propose two methods for the separation of these enantiomers.