Stereoisomers

Stereoisomers

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

Constitutional Isomers

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

Chiral

A molecule that is not superimposable on its mirror image.

Achiral

A molecule that is superimposable on its mirror image.

different, the same

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

A, B

Select all of the structures that are achiral.

True

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

3

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

enantiomers

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

4, stereogenic

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

B, E

Select all of the structures that are chiral.

True

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

tetrahedral stereogenic

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

True

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

False (May or may not be)

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

B, C

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

True

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

one tetrahedral stereogenic center

A molecule is always chiral if it contains ________.

False

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

A, C, D

Which of the illustrated molecules contain tetrahedral stereogenic centers?

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?

the same, different, different

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

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).

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.

A, D

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

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 ________.

True

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

False

(T/F) A meso compound is chiral.

achiral, two or more

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

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.

Enantiomers

What is the stereochemical relationship between the two compounds shown?

A, C, D

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

A, C

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

different, identical

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

chiral, plane-polarized

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

True

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

False

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

enantiomers, different

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

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.

active, inactive

Chiral compounds are optically ________, while achiral are ________.

Racemic mixture

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

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 _____.

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.

True

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

False

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

False

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

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

Enantomeric excess (ee)

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

concentration in g/mL

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

optical purity

Another term for enantiomeric excess is ________.

not, chemical

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

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.

Molecular shape

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

chiral

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

True

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

S, S, S

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

Enantiomers

How are the following compounds related?

A, D, B, C

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

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.