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5. Chirality

Optical Activity

5. Chirality

Optical Activity

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Specific rotation vs. observed rotation.

Specific rotation vs. observed rotation.

Johnny Betancourt

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Textbook Question

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

Textbook Question

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?

Textbook Question

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

Textbook Question

Which of the following are optically active?

Textbook Question

b. Which stereoisomers are optically inactive?

Textbook Question

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

Textbook Question

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

Textbook Question

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?

Textbook Question

(••••) 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.

Textbook Question

(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?

Textbook Question

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

Textbook Question

Draw the structure for a compound with molecular formula C₂H₂I₂F₂

c. that is optically active.

Textbook Question

A solution of 0.50 g of (−)-epinephrine (see Figure 5-16) dissolved in 10.0 mL of dilute aqueous HCl was placed in a 20-cm polarimeter tube. Using the sodium D line, the rotation was found to be −5.1° at 25 °C.

Determine the specific rotation of epinephrine.

Textbook Question

Calculate the specific rotations of the following samples taken at 25 °C using the sodium D line.

a. (a) 1.00 g of sample is dissolved in 20.0 mL of ethanol. Then 5.00 mL of this solution is placed in a 20.0-cm polarimeter tube. The observed rotation is 1.25° counterclockwise.

Textbook Question

Calculate the specific rotations of the following samples taken at 25 °C using the sodium D line.

(b) 0.050 g of sample is dissolved in 2.0 mL of ethanol, and this solution is placed in a 2.0-cm polarimeter tube. The observed rotation is clockwise 0.043°.

Textbook Question

If you had the two enantiomers of carvone in unmarked bottles,

could you use just your nose and a polarimeter to determine a. whether it is the (+) or (−) enantiomer that smells like spearmint b. whether it is the (R) or (S) enantiomer that smells like spearmint? c. With the information given in the drawings of carvone above, what can you add to your answers to (a) and (b)?

Textbook Question

Draw the mirror images of glucose and fructose. Are glucose and fructose chiral? Do you expect them to be optically active?

Textbook Question

Draw the mirror images of glucose and fructose. Are glucose and fructose chiral? Do you expect them to be optically active?

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