Chapter 5 OCHEM

Which of the following are diastereomers of the compound shown? (Select all that apply.)

(3S, 4S)-3,4-dimethylheptane (3R, 4R)-3,4-dimethylheptane

If the observed rotation (α) is +23° for compound A when measured in a 1 dm sample tube containing 1.0 g of A in 10 mL of water, what is the specific rotation [α] of compound A? Multiple choice question.

+230

If the observed rotation (α) is -37° for compound B when measured in a 10 cm sample tube containing 0.5 g of B in 2.0 mL of water, what is the specific rotation [α] of compound B?

-148

Compound X is found to have an observed rotation of +25°. Under the same experimental conditions the enantiomer of X will have an observed rotation of _____.

-25°

Click and drag on elements in order Assign a priority (1, 2, 3, or 4) to each group bonded to the stereogenic center in the molecule shown. Place the group with the highest priority (1) at the top of the list and the group with the lowest priority (4) at the bottom of the list.

1- NH2 2- CH2OH 3- CH3 4- H

If pure (R)-alanine has a specific rotation of -8.5°and a sample prepared in the lab has a specific rotation of -1.0°, determine the enantiomeric excess (ee) of the sample.

12%

A mixture contains 65% of a compound and 35% of its enantiomer. The ee of the mixture is equal to %.

30

A chiral molecule has a specific rotation of -23.5° and a prepared sample has a specific rotation of -18.5°. What is the enantiomeric excess (ee) of the prepared sample?

79%

Consider a mixture of two enantiomers, A and B. If the mixture contains an excess amount of B and has an ee of 84%, how much of each enantiomer is present?

8% A; 92% B

A mixture contains 90% of A and 10% of its enantiomer B. The enantiomeric excess (ee) of the mixture is _____.

80%

Consider a mixture of two enantiomers, A and B. If the mixture contains an excess amount of A and has an ee of 72%, how much of each enantiomer is present?

86% A; 14% B

Which of the structures A-D are diastereomers of compound X? (Select all that apply.)

A C

Consider the molecules drawn in the diagram below. Select all of the structures that are meso compounds.

A C D

Select all that apply Consider the structures shown in the diagram. Which of these molecules contain a stereogenic center with the R configuration? (Select all that apply.)

A and D

Which of the following statements correctly describe a meso compound? (Select all that apply.)

A meso compound is achiral. A meso compound generally contains a plane of symmetry. A meso compound contains two or more stereogenic centers.

Which of the following correctly explains why a meso compound is achiral?

A meso compound is superimposable on its mirror image.

A meso compound possesses which of the following structural features? (Select all that apply.)

A plane of symmetry Two or more stereogenic centers

Which of the following statements is correct about a polarimeter?

A polarimeter measures a molecule's optical rotation. A polarimeter allows plane-polarized light to travel through a sample tube containing an organic molecule. Light is passed through a polarizer to allow light in only one plane to pass through a sample.

Which of the following statement correctly describes the role of a polarizer?

A polarizer allows light only in one plane to pass through, resulting in plane-polarized light.

Select all statements that correctly describe a racemic mixture.

A racemic mixture is also known as a racemate. A racemic mixture is a 1:1 mixture of two enantiomers.

Which of the following accurately defines a meso compound? Multiple choice question.

An achiral compound that contains tetrahedral stereogenic centers

If the lowest priority group on a stereogenic center is in front of the structure (on a wedged bond) rather than at the back (on a dashed bond), how would the configuration of the stereogenic center be assigned?

Assign the configuration as if the lowest priority group were at the back and reverse the answer.

Compound A is chiral and has an optical rotation of +100 and a melting point of 1230C. The physical properties of A are compared to those of its enantiomer, B, and to those of a racemic mixture of A and B. Which of the following statements about A, B, and the racemate are correct? Select all that apply.

B has a melting point of 1230C. The racemic mixture has a melting point that may be different from A and B. The racemic mixture has an optical rotation of 0°.

The maximum possible number of stereoisomers for a compound with 2 stereogenic centers is equal to . If the compound has a meso form it has only stereoisomers.

Blank 1: 4 or four Blank 2: 3 or three

When naming a molecule with more than one stereogenic center, R and S designations must be assigned to stereogenic center.

Blank 1: every or each

When calculating the enantiomeric excess of a mixture of enantiomers, the [α] of the is divided by the [α] of one .

Blank 1: mixture Blank 2: pure enantiomer or enantiomer

Electromagnetic radiation consists of light waves that oscillate in all directions perpendicular to the direction of travel. A allows light of only one plane to pass through. This light is said to be -polarized.

Blank 1: polarizer, polarizing filter, polariser, or grating Blank 2: plane

The observed rotation of a mixture is 0° because the two rotate plane-polarized light to an equal extent but in opposite directions, so the rotations cancel.

Blank 1: racemic Blank 2: enantiomers

Which of the following physical properties are identical for two enantiomers? (Select all that apply.)

Boiling point Solubility Melting point

Select the statement that correctly describes the interaction of organic compounds with plane-polarized light.

Chiral compounds rotate plane-polarized light while achiral compounds do not.

What is the relationship between the two structures shown?

Constitutional isomers

A pair of molecules that are stereoisomers but not mirror images are called

Diastereomers

A mixture of compounds can be separated by physical methods such as distillation if the compounds have different physical properties. Which of the following can be separated by physical methods? (Select all that apply.)

Diastereomers Constitutional isomers

Select all statements that correctly describe diastereomers.

Diastereomers are not mirror images of each other. Diastereomers have the same molecular formula.

Which of the following are steps needed to find and draw all possible stereoisomers of a compound with two stereogenic centers? (Select all that apply.)

Draw a third possible stereoisomer by switching the positions of any two groups on one stereogenic center only, then draw its mirror image. Draw one stereoisomer, then draw its mirror image.

What is the relationship between the two structures shown?

Enantiomers

What is the stereochemical relationship between the two compounds shown?

Enantiomers

Match each type of isomer to the correct description.

Enantiomers identical physical properties Diasteromers and constitutional isomers different physical properties

Select all statements that correctly describe the physical and chemical properties of the given isomers.

Enantiomers have identical chemical properties. Enantiomers have identical melting points.

Select all statements that correctly describe the relationship between optical rotation and the identity of an enantiomer.

Enantiomers rotate plane-polarized light in opposite directions. Enantiomers rotate plane-polarized light to the same extent.

Is the compound shown a meso compound or is it a chiral compound?

Meso compound

______ is an important property for determining the odor of a molecule.

Molecular shape

Consider the molecule shown in the diagram below. Match each group attached to the stereogenic center with its appropriate priority (1, 2, 3, or 4).

OH Priority 1 CH=CH2 Priority 2 CH3 Priority 3 H Priority 4

Which of the following statements correctly describes the interaction of plane-polarized light with a solution containing an optically inactive compound?

Plane-polarized light passes through a solution of the compound unchanged.

An unknown compound X has two stereogenic centers that each have the R configuration. The diastereomer(s) of X will have the _____ configurations at the stereogenic centers. Select all that apply.

R and S S and R

Designate the configuration of the stereogenic center in the structure shown as R or S.

S

What property of a molecule is most important in determining its odor?

Shape

Which of the following statements correctly describe the biological activity and use of chiral drugs? Select all that apply.

Some chiral drugs are sold as racemic mixtures because it is more cost effective. One enantiomer of a chiral drug can be biologically active and the other can be ineffective. Smaller doses can be used if chiral drugs are sold as a single enantiomer.

Which of the following are meso compounds?

Structure A Structure C

Which of the following are meso compounds?

Structure C

Match the structure of each compound (X and Y) with the correct description of its stereochemical relationship to structure A.

Structure X matches Choice enantiomer of A Structure Y matches Choice diastereomer of A

Match each structure to the correct description of its relationship to compound A.

Structure Y diastereomer of A Structure X enantiomer of A Structure Z identical to A

Which of the following is true about R and S assignments in compounds with two or more stereogenic centers?

The R or S configuration must be assigned to each stereogenic center.

What does enantiomeric excess (ee) directly describe?

The amount of one enantiomer in excess of the racemic mixture.

An organic compound X has a melting point of 1820C and a specific rotation of -12.50. Which of the following statements about the physical properties of the stereoisomers of X are true? (Select all that apply.)

The enantiomer of X has a melting point of 182°C. The diastereomer of X most likely does not have a melting point of 182°C.

Which of the following best defines the enantiomeric excess of a mixture?

The enantiomeric excess indicates how much more there is of one enantiomer in the mixture.

Which of the following statements correctly describes the optical activity of a racemic mixture?

The mixture is not optically active because the two enantiomers cause equal but opposite rotations, which therefore cancel.

What is the observed rotation of a sample?

The observed rotation is the angle (α) by which a chiral compound rotates plane-polarized light in a polarimeter.

Which of the following statements correctly describe the relationship between the physical properties of two pure enantiomers and their racemic mixture?

The optical rotation of the two pure enantiomers would be equal in magnitude and opposite in direction of rotation. The optical rotation of a racemic mixture is 0∘.

Which of the following statements correctly describe the stereoisomers of the cycloalkane shown? (Select all that apply.)

The pair of cis isomers are diasteromers of either trans isomer. The two cis isomers are enantiomers of each other.

Which of the following statements correctly describe the relative physical properties of diastereomers? Select all that apply.

The physical properties of diastereomers are different. Diastereomers have different physical properties because they are not mirror images of each other.

Which of the following statements correctly describe the stereoisomers of the cycloalkane shown? (Select all that apply.)

The two cis isomers are enantiomers of each other. The pair of cis isomers are diasteromers of either trans isomer.

Which of the following best describes the chemical properties of two enantiomers?

Their chemical properties are identical except for their reaction with chiral, non-racemic reagents.

Which of the following best describes the relationship between configuration (R or S) and optical rotation?

There is no relationship between configuration and optical rotation.

Which of the following statements correctly describe two enantiomers? (Select all that apply.)

They have identical solubilities. They have identical melting points.

A molecule with two stereogenic centers has a maximum of four possible stereoisomers. Which of the following statements describes the effect that a meso compound has on the total number of stereoisomers?

When one of the stereoisomers is a meso compound, the total number of stereoisomers is reduced by one.

The equation [α] = αl×cαl×c is used to calculate the specific rotation of a chiral compound. Match each term in the equation with its appropriate description.

[α] specific rotation α observed rotation (°) l length of the sample tube (dm) c concentration (g/mL)

Which of the following equations correctly describes how to calculate the specific rotation of a chiral compound?

[α] = α/l×c

A mixture containing equal amount of two enantiomers is ________.

a racemic mixture a racemate

A meso compound is a(n) ______ compound containing ______ stereogenic centers.

achiral, two or more

Two enantiomers have exactly the same chemical behavior except for their reaction with , non-racemic reagents.

chiral

Match each type of compound with the correct description of its interaction with polarized light.

chiral optically active achiral optically inactive

If a compound rotates plane-polarized light in a direction, the compound is called dextrorotatory, and is labeled d or . Rotation for a levorotatory compound is labeled l or .

clockwise + -

Optically active compounds rotate plane-polarized light. Match the direction of rotation with the correct term.

clockwise dextrorotatory counterclockwise levorotatory

Match each type of isomer with the correct definition.

constitutional isomers same molecular formula, different connectivity of atoms enantiomers nonsuperimposable mirror images diastereomers stereoisomers that are not mirror images stereoisomers same formula and structure, different 3-D arrangement

Two compounds can usually be separated only if their physical properties are different. Physical methods such as distillation will allow the separation of _____ and/or constitutional isomers but not of _____.

diastereomers, enantiomers

Structural isomers can have _______ chemical and physical properties, whereas enantiomers have _______ chemical and physical properties except their interaction with chiral substances.

different; identical

Which of the following equations correctly relates enantiomeric excess and optical rotation?

ee = [α] mixture / [α] pure enantiomer x 100%

The percentage enantiomeric excess (%ee) of a mixture indicates how much of one is present in excess of the mixture.

enantiomer racemic

The ___ excess, also called the optical ____, tells how much more there is of one enantiomer in a mixture.

enantiomeric purity

Two _____ always rotate plane-polarized light to an equal extent but in _____ direction(s).

enantiomers, opposite

Match each stereoisomeric pair with the correct relationship between their configurations.

identical compounds matches Choice identical R,S designations at all stereogenic centers enantiomers matches Choice opposite R,S designations at all stereogenic centers diastereomers matches Choice same R,S designation for at least one stereogenic center and opposite R,S designation for at least one stereogenic center

The first step in drawing all possible steroisomers for a compound with two stereogenic centers is to draw one stereoisomer by arbitrarily arranging substituents around both sterogenic centers, and then draw its __ image.

mirror

Diastereomers are __ mirror images of each other and therefore their ___ properties are different, including optical rotation.

not physical

The amount by which an optically active compound rotates the plane of polarized light is measured as an angle. This angle is given the symbol α and is called the rotation.

observed

Which of the following parameters are included in the calculation of specific rotation [α] using the equation [α] = α/cl ? Select all that apply.

observed rotation α in ° concentration in g/mL length of sample tube in dm

A compound that rotates the plane of polarized light is said to be _____.

optically active

A _______ is the instrument that allows plane-polarized light to travel through a solution of a compound and measures the compound's optical rotation.

polarimeter

Many chiral drugs are sold as a ____ . It is difficult and costly to separate the two _______, since they have the same physical properties.

racemic mixture enantiomer

The _____ rotation denoted by [α], is a physical constant that is calculated by measuring the _____ rotation of a sample in a tube with a defined length at a specific temperature, concentration, and wavelength.

specific, observed

Fill in the blank question. Two compounds that have the same structure but a different three-dimensional arrangement of atoms are called -isomers, while two compounds with the same formula but different connectivities of atoms are called isomers.

stereo constitutional

A meso compound contains at least _____ tetrahedral stereocenters and is _____ because it contains a plane of symmetry.

two achiral