Optical Activity: Videos & Practice Problems

For each of the following compounds, draw a structure and identify if it can show optical acitivity.
a. 2-bromobutane
b. cis-1,2-dichlorocyclohexane

(R)-Carvone is monoterpene responsible for the smell of spearmint. Considering the fact that (R)-carvone rotates the plane-polarized light in the counter-clockwise direction, answer the following questions:

(a) Should (R)-carvone be referred to as (d) or (l)?

(b) Should it be referred to as (+) or (−)?

(c) What would be the direction of rotation (d or l; + or −) for (S)-carvone?

Determine which of the given isomers of butane-2,3-diol is optically inactive. Justify your answer.

(S)-Amphetamine is a commercially available drug used as a CNS stimulant. Considering the fact that (S)-amphetamine rotates the plane-polarized light in the clockwise direction, answer the following questions:

(a) Should (S)-amphetamine be referred to as (d) or (l)?

(b) Should it be referred to as (+) or (−)?

(c) What would be the direction of rotation (d or l; + or −) for (R)-amphetamine?

Looking at the absolute configuration of (R)-2-chlorobutane, determine whether it rotates plane-polarized light clockwise or counter-clockwise.

Among the following structures, identify the stereoisomers which are optically inactive.

Among the following structures, identify the optically active stereoisomers.

Determine whether (S)-(−)-2-methyl-1-butanol and (S)-(+)-2-methylbutanoic acid are dextrorotatory or levorotatory.

(S)-1-Bromo-2-methylpentane reacts with the hydroxide ion to produce 2-methyl-1-pentanol without any change in spatial arrangement around the stereocenter. The resulting alcohol rotates the plane-polarized light clockwise. Determine the absolute configuration of (−)-2-methyl-1-pentanol.

Explain the relation between absolute configuration (R and S) and optical rotation (+) and (−).

A compound has a molecular formula of C₂H₂Br₂Cl₂. Draw the possible structures of the compound if it is optically active.

A sample of (–)-1-fluoro-2-methylbutane was analyzed in a polarimeter. The sample was prepared by dissolving 7.5 g of the compound to form a 50.0 mL solution and placing it in a 20 cm polarimeter tube. The observed rotation at 20°C is 0.173°. Calculate the specific rotation of (–)-1-fluoro-2-methylbutane.

A 2.50 g sample is dissolved in 50.0 mL of ethanol. Then, 10.0 mL of this solution is placed in a 10.0-cm polarimeter tube. The observed rotation is 2.36° counterclockwise. Calculate the specific rotation.

A 1.5 g sample is dissolved in 30 mL of ethanol. Then, 10 mL of this solution is placed in a 10-cm polarimeter tube. The observed rotation is 0.085° clockwise. Calculate the specific rotation.

If there are two enantiomers of limonene in unmarked bottles.

a. What is the possible way to recognize which one is a (+) enantiomer and which one is a (−) enantiomer?
b. What is the configuration of (+)-limonene which smells like orange and (−)-limonene which smells like lemon?

Write the structures of the mirror images of D-galactose and D-mannose. Do you think D-galactose and D-mannose are chiral and optically active?

In an experiment, it was discovered that the following compound had a specific rotation [⍺] of -25° at 27°C. At 120°C, the specific rotation of the compound was measured to be 0°. After cooling to 27°C, the specific rotation of the compound was measured again and found to be 0°. Justify these observations.

What is optical activity, and why is it significant in relation to chiral molecules?

Which of the following describes how a polarimeter functions in measuring optical rotation?

A solution with a specific rotation of +10 degrees is present at a concentration of 2 g/mL in a polarimeter tube of 5 cm length. What is the observed rotation?

Which statement correctly differentiates between dextrorotary and levorotary rotations?