Chapter 5 Smartbook

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°

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

30

A carbon atom bonded to (3 or more/4) different groups is a tetrahedral (achiral/stereogenic).

4; stereogenic

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

80%

(Stereoisomers/Constitutional isomers) may contain different functional groups and are assigned different IUPAC names.

Constitutional isomers

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

False

True or false: Stereoisomers are isomers that differ in connectivity of their atoms.

False

True or false: When assigning priorities, a C(triplebond)C 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.

False; ONE atom of a higher atomic number in a group gives that group the higher priority (not combined atoms)

Select the statement that correctly describes the interaction of organic compounds with plane-polarized light. a) Chiral compounds rotate plane-polarized light while achiral compounds do not b) Chiral compounds rotate plane-polarized light much more than do achiral compounds c) Chiral compounds rotate plane-polarized light in the opposite direction to achiral compounds d) Chiral compounds do not rotate plane-polarized light while achiral compounds do

a) Chiral compounds rotate plane-polarized light while achiral compounds do not

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. a) If two atoms on a stereogenic center are the same, assign priority based on the atomic number of the atoms bonded to these atoms b) If two atoms on a stereogenic center are the same, assign priority based on the mass number of the atoms bonded to these atoms c) fFor atoms bonded to the stereogenic center, an atom with a lower atomic number has a higher priority d) Assign priorities to the groups bonded to the stereogenic center in order of decreasing group size e) For atoms bonded to the stereogenic center, an atom with a higher atomic number has a higher priority

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

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. a) S and R b) R and S c) S and S d) R and R

a) S and R; b) R and S

Which of the following statements correctly describe constitutional isomers and stereoisomers? (Select all that apply.) a) Stereoisomers differ only in the way atoms are oriented in space b) Constitutional isomers differ in the way the atoms are connected to each other c) Constitutional isomers differ only in the way atoms are oriented in space d) Stereoisomers differ in the way the atoms are connected to each other

a) Stereoisomers differ only in the way atoms are oriented in space; b) Constitutional isomers differ in the way the atoms are connected to each other

What does enantiomeric excess (ee) directly describe? a) The amount of one enantiomer in excess of the racemic mixture b) The amount of one enantiomer over the other

a) The amount of one enantiomer in excess of the racemic mixture

Which of the following best defines the enantiomeric excess of a mixture? a) The enantiomeric excess indicates how much more there is of one enantiomer in the mixture b) The enantiomeric excess indicates how much more soluble one enantiomer is than the other c) The enantiomeric excess indicates how much more reactive one enantiomer is than the other d) The enantiomeric excess tells how much more of one enantiomer must be added to achieve a racemic mixture

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

Which of the following describes the chemical properties of two enantiomers? a) Their chemical properties are identical except for their reaction with chiral, non-racemic reagents b) All of their chemical properties are the same c) Their chemical properties may or may not be the same, just like any two compounds that are different d) All of their chemical properties are different

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

Which of the following statements correctly describe constitutional isomers? (Select all that apply.) a) They may contain different functional groups b) they differ in the way the atoms are connected together c) they typically give different products in chemical reactions d) They have different IUPAC names e) They have the same physical properties

a) They may contain different functional groups; b) they differ in the way the atoms are connected together; c) they typically give different products in chemical reactions; d) They have different IUPAC names

What is a tetrahedral stereogenic center? a) a carbon atom bonded to four different atoms or groups b) a carbon atom bonded to four identical atoms c) a carbon atom bonded to four identical groups

a) a carbon atom bonded to four different atoms or groups

What are enantiomers? a) mirror image molecules that are not superimposable b) molecules that are not mirror images but that are superimposable c) mirror image molecules that are superimposable d) molecules that are not mirror images and are not superimposable

a) mirror image molecules that are not superimposable

A meso compound is a(n) (chiral/achiral) compound containing (no/one/two or more) stereogenic centers.

achiral; two or more

Chiral molecules are optically _______.

active

Which of the following accurately defines a meso compound? a) A chiral compound that contains no tetrahedral stereogenic centers b) An achiral compound that contains tetrahedral stereogenic centers c) An achiral compound that contains no tetrahedral stereogenic centers d) A chiral compound that contains tetrahedral stereogenic centers

b) An achiral compound that contains tetrahedral stereogenic centers

Which of the following are steps used to test for chirality? (Select all that apply.) a) Draw the molecule in two dimensions b) Draw or build the mirror image of the molecule c) Try to align all the bonds and atoms in a two-dimensional drawing of the molecule and its mirror image d) Try to align all of the bonds and atoms in the molecule with those of its mirror image e) Draw the molecule in three dimensions or build a model.

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

How are priorities assigned to each group bonded to a tetrahedral stereogenic center? (Select all that apply.) a) If two isotopes are bonded to the sterogenic center, the isotope with the lower mass number has a higher priority b) If two atoms attached to a sterogenic center are the same, assign priority based on the atomi number of the atoms bonded to these atoms c) 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 d) If two isotopes are bonded to the sterogenic center, the isotope with the higher mass number has a higher priority

b) If two atoms attached to a sterogenic center are the same, assign priority based on the atomi number of the atoms bonded to these atoms; c) 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; d) If two isotopes are bonded to the sterogenic center, the isotope with the higher mass number has a higher priority

Which of the following are steps for assigning R or S to a stereogenic center? (Select all that apply.) a) Orient the molecule with the highest priority group to the back b) Orient the molecule with the lowest priority group to the back c) Assign priorities from 1 to 4 to each group bonded to the stereogenic center. d) Trace a circle from priority group 3→2→1

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

Which property of a molecule is most important in determining its odor? a) Density b) Shape c) Functional groups presnt d) Size

b) Shape

Which of the following statements correctly describe the biological activity and use of chiral drugs? Select all that apply. a) Two enantiomers of a chiral drug typically have identical biological activity b) Some chiral drugs are sold as a racemic mixture because it is more cost effective c) smaller doses can be used if chiral drugs are sold as a single enantiomer d) one enantiomer of a chiral drug can be biologically active in the other can be ineffective

b) Some chiral drugs are sold as a racemic mixture because it is more cost effective ; c) smaller doses can be used if chiral drugs are sold as a single enantiomer; d) one enantiomer of a chiral drug can be biologically active in the other can be ineffective

What is observed rotation of a sample? a) he observes rotation is the angle (A) by which an achiral compound rotates plane-polarized light in a polarimeter b) The observed rotation is the angle (a) by which a chiral compound rotates plane-polarized light in a polarimeter c) The observed rotation is the angle (a) by which an achiral compound rotates ordinary light in a polarimeter d) The observed rotation is the angle (a) by which a chiral compound rotates ordinary light in a polarimeter

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

Which of the following physical properties are identical for two enantiomers? (Select all that apply.) a) Interaction with plane-polarized light b) melting point c) boiling point d) solubility

b) melting point; c) boiling point; d) solubility

A compound that rotates the plane of polarized light is said to be: a) optically inactive b) optically active c) A racemic mixture

b) optically active

Select the statement that correctly describes chiral and achiral molecules. a) An achiral molecule has no mirror image b) An achiral molecule cannot be superimposed upon its mirror image c) A chiral molecule cannot be superimposed upon its mirror image

c) A chiral molecule cannot be superimposed upon its mirror image

Which of the following statements correctly describe the relative physical properties of diastereomers? Select all that apply. a) The physical properties of diastereomers are identical b) Diastereomers have identical physical properties because they have identical functional groups c) Diastereomers have different physical properties because they are not mirror images of each other d) The physical properties of diastereomers are different e) Diastereomers have different properties because they are not superimposable mirror images of each other

c) Diastereomers have different physical properties because they are not mirror images of each other; d) The physical properties of diastereomers are different

Select all statements that correctly describe diastereomers. a) Diastereomers are mirror images of each other b) Diastereomers differ in the way that their atoms are connected to each other c) Diasteromers have the same molecular formula d) Diastereomers are not mirror images of each other

c) Diasteromers have the same molecular formula; d) Diastereomers are not mirror images of each other

Select all statements that correctly describe the physical and chemical properties of the given isomers. a) Constitutional isomers have identical melting points b) Enantiomers have identical interactions with chiral substances c) Enantiomers have identical melting points d) Enantiomers have identical chemical properties

c) Enantiomers have identical melting points; d) Enantiomers have identical chemical properties (except their interaction with chiral substances)

Which of the following statements correctly describes the optical activity of a racemic mixture? a) The mixture is optically active because each enantiomer in the mixture is optically active b) The mixture is not optically active because a mixture of two enantiomers is achiral c) The mixture is not optically active because the two enantiomers cause equal but opposite rotations, which therefore cancel.

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

Stereoisomers that are mirror images of each other and are not superimposable are called ____________. a) diastereomers b) chiral c) enantiomers d) meso compounds

c) enantiomers

Which of the following parameters are included in the calculation of specific rotation [a] using the equation [a]=a/(cl)? Select all that apply. a) concentration in mol/L b) atmospheric pressure c) observed rotation a in ° d) concentration in g/mL e) length of sample tube in dm

c) observed rotation a in °; d) concentration in g/mL; e) length of sample tube in dm

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

If a compound rotates plane-polarized light in a __________ direction, the compound is called dextrorotary, and is labeled d or ____. Rotation for a levrorotary compound is labeled l or ___.

clockwise; +; -

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 ________. a) 1, S, R b) 1, R, S c) 4, S, R d) 4, R, S

d) 4, R, S

Shut the following statements correctly describes the interaction of plain polarized light with a solution containing an optically inactive compound? a) the compound does not transmit polarized light into solution b) The compound does not absorb plane-polarized light in solution c) Plane-polarized light is rotated as it passes through a solution of the compound d) Plane-polarized light passes through a solution of the compound unchanged

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

Optically active compounds rotate plane-polarized light. Clockwise is (dextrorotary/levorotary) and counterclockwise is (dextrorotary/levorotary).

destrorotary; levorotary

A pair of molecules that are steroisomers but not mirror images are called _________.

diastereomers

Structural isomers can have (identical/different) chemical and physical properties, whereas enantiomers have (different/identical) chemical and physical properties except their interaction with chiral substances.

different; identical

Isomers are (the same/different) compound(s) with (the same/different) molecular formula(s).

different; the same

___________ is an important property for determining the odor of a molecule. a) Solubility b) Melting point c) Density e) Molecular shape

e) Molecular shape

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 the ___________ direction(s).

enantiomers; opposite

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

higher; 2

Different compounds with the same molecular formula are called ___________.

isomers

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 of a and is called the __________ rotation.

observed

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; enantiomers

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 cance.

racemic; enantiomers

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

specific; observed

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