Chapter 5

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

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

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

Place the following steps used to test chirality in the correct order. The first step should be placed at the top of the list and the last step should be placed at the bottom.

1) Draw the molecule in three dimensions. 2) Draw the mirror image of the molecule 3) Try to align all bonds and atoms in the molecule with those of its mirror image

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

30

When determining the configuration of a stereogenic center, priorities are assigned to the four attached groups. The group designated priority _____ is placed at the back, and a circle is traced through the remaining groups, from 1 → 2 → 3. If this circle is clockwise the configuration is _____; if counterclockwise, the configuration is _____.

4, R, S

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

Select the statement that correctly describes chiral and achiral molecules.

A chiral molecule cannot be superimposed upon its mirror image.

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.

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.

What is a tetrahedral stereogenic center?

A tetrahedral stereogenic center is a carbon atom bonded to four different atoms or groups.

Which statement(s) about the compound shown (D = deuterium) is/are correct? Select all that apply.

C2 is a stereogenic center, since it has four different groups attached to it. C2 of the molecule has the R configuration.

A particular three-dimensional arrangement of atoms is called a _____.

CONFIGURATION

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.

Which of the following statements correctly describe constitutional isomers and stereoisomers? (Select all that apply.)

Constitutional isomers differ in the way the atoms are connected to each other. Stereoisomers differ only in the way atoms are oriented in space.

the term --- specifically describes stereoisomers that are NOT mirror images of each other.

Diastereomers

Select all statements that correctly describe diastereomers.

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

What are enantiomers?

Enantiomers are mirror image molecules that are not superimposable.

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

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

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.

rue or false: When assigning priorities, a CΞC group would be assigned a higher priority than a C=O group because 3 C atoms have a higher combined atomic number than 2 O atoms.

F

Many chiral drugs are sold as a single enantiomer.Blank 1Blank 1 single enantiomer. , Incorrect Unavailable. It is difficult and costly to separate the two mixturesBlank 2Blank 2 mixtures , Incorrect Unavailable, since they have the same physical properties.

FBlank 1: racemic mixture or racemate Blank 2: enantiomers

Which of the following statements correctly describe how to assign a priority to each group bonded to a stereogenic center when assigning R/S configurations? Select all that apply.

If two atoms on a stereogenic center are the same, assign priority based on the atomic number of the atoms bonded to these atoms. For atoms bonded to the stereogenic center, an atom with a higher atomic number has a higher priority.

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

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

Which of the following are steps for assigning R or S to a stereogenic center? (Select all that apply.)

Orient the molecule with the lowest priority group to the back. Assign priorities from 1 to 4 to each group bonded to the stereogenic center.

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.

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

Racemic Enantiomers

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.

S and R R and S

Select all of the statements that correctly describe stereoisomers

Stereoisomers differ in the way that their atoms are oriented in space. Steroisomers have the same IUPAC names except for a prefix like cis or trans.

True or false: A chiral molecule and a stereogenic carbon are not the same thing.

TRUE

Which one of the following statements is correct when assigning priorities to the substituents on the stereogenic center shown?

The -CH2OH group has a higher priority than the alkene group because O has a higher atomic number than C.

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 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.

Two compounds that are enantiomers have _____ molecular formula(s), _____ structure(s), and therefore _____ prefixes are used in their names. Multiple choice question.

The same diff diff

Which of the following correctly defines the term stereochemistry?

The three-dimensional structure of a molecule

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.

hich 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 why enantiomers have different prefixes in their IUPAC names?

They are different molecules with the same bond connectivity but each with a different three-dimensional orientation of atoms.

Which of the following statements correctly describe constitutional isomers? (Select all that apply.)

They differ in the way the atoms are connected together. They give different products in chemical reactions. They have different IUPAC names. They may contain different functional groups.

Which of the following statements correctly describes the C atom bearing the OH group in the compound shown?

This C is a stereogenic center because the 2 CH2 groups on either side of it are not identical.

How are priorities assigned to each group bonded to a tetrahedral stereogenic center? (Select all that apply.)

To assign a priority to an atom that is part of a multiple bond, treat the multiple bond as an equivalent number of single bonds. If two isotopes are bonded to the stereogenic center, the isotope with the higher mass number has a higher priority. If two atoms attached to a stereogenic center are the same, assign priority based on the atomic number of the atoms bonded to these atoms.

Which of the following are steps used to test for chirality? (Select all that apply.)

Try to align all of the bonds and atoms in the molecule with those of its mirror image. Draw or build the mirror image of the molecule. Draw the molecule in three dimensions or build a model.

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

[α] = αl×c

The term configuration refers to _____.

a particular three-dimensional arrangement of atoms.

A mixture containing equal amount of two enantiomers is ________.

a racemate a racemic mixture

All 3-D objects can be classified as either chiral or

achiral

achiral molecule

can be superimposed on its mirror image

They are nonsuperimposable on their mirror images

chiral

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

chiral

A molecule is ----if it cannot be superimposed on its mirror image, but a carbon atom bonded to four different groups is a ---- center.

chiral stereogenic

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

chiral- optically active achiral- optically inactive

dextrorotatory levorotatory

clockwise counterclockwise

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 + -

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

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

may contain different functional groups and are assigned different IUPAC names.

constitutional isomers

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 ----mixture.

enantiomer racemic

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

enantiomeric purity

Stereoisomers that are mirror images of each other and are not superimposable are called ______. Multiple choice question.

enantiomers

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

enantiomers, opposite

A carbon atom bonded to _____ different groups is a tetrahedral _____ center.

four stereogenic

No stereogenic centers One tetrahedral stereogenic center Two or more stereogenic centers

generally not chiral Chiral May or may not be chiral

When assigning priorities to groups, a C=O group is assigned a _____ priority than a CH2OH group because the C=O C is treated as if it is bonded to _____ O atom(s).

higher, 2

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

identical boiling points and solubilities

Different compounds with the same molecular formula are called

isomers

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

melting boiling solubility

Diastereomers are not ---of each other and therefore their ---properties are different.

mirror images chemical

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

mixture pure enantiomer or enantiomer

chiral molecule

nonsuperimposable upon its mirror image

he 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 dBlank 1Blank 1 d , Incorrect Unavailable rotation.

observed

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

optically active

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

shape

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