5. Chirality

Which of the following types of compounds is most likely to undergo racemization when treated with aqueous acid or base ($H{2}_{}O$ + $H+$ or $\mathrm{OH}-$)?

Choose the best explanation for why a racemic mixture does not rotate plane-polarized light.

Given the compound ${\mathrm{CH}}_3\mathrm{CHBrClF}$, determine whether it is optically active or optically inactive.

a. Is (R)-lactic acid dextrorotatory or levorotatory?

b. Is (R)-sodium lactate dextrorotatory or levorotatory?

Explain how R and S are related to (+) and (-).

The reaction of (R)-1-iodo-2-methylbutane with hydroxide ion forms an alcohol without breaking any bonds to the asymmetric center. The alcohol rotates the plane of polarization of plane-polarized light counterclockwise. What is the configuration of (+)-2-methyl-1-butanol?

Which of the following are optically active?

Which stereoisomers are optically inactive?

Make a model of each compound, draw it in its most symmetric conformation, and determine whether it is capable of showing optical activity.

a. 1-bromo-1-chloroethane

b. 1-bromo-2-chloroethane

Based on the absolute configuration of (S)-butan-2-ol, what can you say about the direction it rotates plane-polarized light?

Naproxen is a commercially available anti-inflammatory sold under the name Aleve.

(b) Given that naproxen rotates plane-polarized light in the clockwise direction, should it be referred to as (d) or (l)?

(c) Is it (+) or (-)?

(d) What direction (d or l; + or −) would you expect the enantiomer of naproxen to rotate plane-polarized light?

When the following substituted biphenyl was synthesized, it was found to have a specific rotation [α] of -23° at 25°C . When the specific rotation was measured at 100°C the compound had a specific rotation of 0° . Upon cooling back to 25°C the specific rotation was measured again, resulting in [α] = 0°. Explain these results.

(R)-Limonene is a cyclic terpene responsible for the smell of oranges and other citrus fruits.

(a) Given that (R)-limonene rotates plane-polarized light in the clockwise direction, should it be referred to as (d) or (l)?

(b) Is it (+) or (-)?

(c) What direction (d or l; + or −) would you expect (S)-limonene to rotate plane-polarized light?

Which of the following diastereomers of hexane-2,5-diol is optically inactive? Why?