Chapter 5: Stereoisomers

True

(T/F) A chiral molecule and a stereogenic carbon are not the same thing.

True

(T/F) A meso compound contains two or more stereogenic centers.

False

(T/F) A meso compound is chiral.

False

(T/F) All dextrorotatory compounds have the S configuration.

False

(T/F) All levorotatory compounds have the R configuration.

True

(T/F) Chiral compounds rotate plane-polarized light while achiral compounds do not.

True

(T/F) Constitutional isomers give different products in chemical reactions.

True

(T/F) Enantiomers are mirror image molecules that are not superimposable.

False

(T/F) Enantiomers interact identically with plane-polarized light.

False

(T/F) If two isotopes are bonded to the stereogenic center, the isotope with the lower mass number has a higher priority.

True

(T/F) Smaller doses can be used if chiral drugs are sold as a single enantiomer.

True

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

False

(T/F) The observed rotation is the angle (α) by which an achiral compound rotates plane-polarized light in a polarimeter.

True

(T/F) There is no relationship between configuration and optical rotation.

True

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

False (May or may not be)

(T/F) Two or more stereogenic centers are usually chiral.

False

(T/F) 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.

tetrahedral stereogenic

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

4, stereogenic

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

achiral, two or more

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

Racemic mixture

A mixture that contains equal amounts of the (+) and (-) enantiomers and thus are not optically active.

one tetrahedral stereogenic center

A molecule is always chiral if it contains ________.

Chiral

A molecule that is not superimposable on its mirror image.

Achiral

A molecule that is superimposable on its mirror image.

S and R, R and S

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.

optical purity

Another term for enantiomeric excess is ________.

active, inactive

Chiral compounds are optically ________, while achiral are ________.

A, C, D

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

A, D

Consider the structures shown in the diagram. Which of these molecules contain a stereogenic center with the R configuration?

not, chemical

Diastereomers are ________ mirror images of each other and therefore their ________ properties are different.

Enantiomers

How are the following compounds related?

clockwise, +, -

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 _____.

concentration in g/mL

In the equation for specific rotation, [a] = a/lc, c stands for ________.

different, the same

Isomers are ________ compound(s) with ________ molecular formula(s).

racemic mixture, enantiomers

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

Enantomeric excess (ee)

Measurement of how much one enantiomer is present in excess of the racemic mixture

A, D, B, C

Rank the following groups in order of decreasing priority (highest to lowest).

A, B

Select all of the structures that are achiral.

B, E

Select all of the structures that are chiral.

enantiomers

Stereoisomers that are mirror images of each other and are not superimposable are called _________.

different, identical

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

specific, observed

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.

observed

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.

chiral

The chemical properties of enantiomers are identical except for their reaction with ________, non-racemic reagents.

chiral, plane-polarized

The observed rotation is the angle (α) by which a ________ compound rotates ________ light in a polarimeter.

Constitutional Isomers

These isomers differ in the way the atoms are connected to each other.

Stereoisomers

These isomers differ only in the way atoms are oriented in space.

S, S, S

This compound is (2__, 3__, 4__)-2,3,4-tribromohexane

S, R, S

This compound is (2__, 3__, 4__)-3,4-dibromo-2-pentanol.

R, R, S

This compound is (2__, 4__, 5__)-2,5-dibromo-4-methylheptane.

3

To test for chirality, you must first draw the molecule in (2/3) dimensions or build a model.

enantiomers, different

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

the same, different, different

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

C1 is bonded to identical alkyl groups that happen to be part of a ring.

What best explains why C1 of methylcycloheptane (shown) is not a stereogenic center?

Enantiomers

What is the stereochemical relationship between the two compounds shown?

higher, 2

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).

4, R, S

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, C, D

Which of the illustrated molecules contain tetrahedral stereogenic centers?

B, C

Which of the marked atoms in the structure shown are tetrahedral stereogenic centers?

A, C

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

Molecular shape

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