Chapter 3

Question 1

Chiral object

Answer 1

Not superposable on its mirror image

Question 2

Achiral object

Answer 2

Lacks chirality. An object with a superposable mirror image.

Question 3

Plane of symmetry

Answer 3

An imaginary plane passing through an object dividing it such that one half is the reflection of the other half.

Question 4

Center of symmetry

Answer 4

A point so situated that identical components of the object are located on opposite sides and equidistant from the point along any axis passing through that point.

Question 5

Stereoisomers

Answer 5

Have the same connectivity of atoms but different spatial arrangement of their atoms

Question 6

Conformational isomers

Answer 6

stereoisomers that interconvert by rotation along single bonds

Question 7

Configurational isomers

Answer 7

stereoisomers that do not interconvert at room temperature because their interconversion would require the breaking of individual single or double bonds

Question 8

Enantiomers

Answer 8

Stereoisomers that are nonsuperposable mirror images

Question 9

Diastereomers

Answer 9

Stereoisomers that are not mirror images

Question 10

Atropisomers

Answer 10

enantiomers or diastereomers that differ because of hindered rotation along a single bond

Question 11

Stereocenter

Answer 11

An atom about which exchange of two groups produces a stereoisomers

Question 12

Chiral center

Answer 12

A tetrahedral atom with four different groups bonded to it. A specific type of stereocenter.

Question 13

Absolute configuration

Answer 13

Which of the two possible isomers an enantiomer is (that is whether it is the right- or left- handed isomer)

Question 14

R,S system

Answer 14

A set of rule for specifying absolute configuration about a chiral center

Question 15

Priority rules:

Answer 15

1) Priority is assigned based on atomic number. The higher the atomic number, the higher the priority.
2) If priority cannot be assigned on the basis of the atoms bonded to the chiral center (because of a tie), continue until a priority can be assigned. If two carbons have substituents of the same priority, priority is assigned to the carbon that has more of the higher priority substituents.
3) Atoms participating in a double or triple bond are considered to be bonded to an equivalent number of similar “phantom” atoms by single bonds; that is, atoms of the double bond are duplicated and atoms of a triple bond are triplicated. The phantom atoms are bonded to no other atoms.
4) Priority assignment is made at the first point of different between groups.

Question 16

For a molecule with n chiral centers, the maximum number of stereoisomers possible is:

Answer 16

2^n

Question 17

Two steroisomers are enantiomers if:

Answer 17

all the chiral centers have the opposite configuration

Question 18

If even one chiral center is the same between two stereoisomers:

Answer 18

They are diastereomers

Question 19

Meso compound

Answer 19

Contains two or more chiral centers bonded in such a way that it is a chiral. Usually have an internal plane of symmetry.

Question 20

Fischer projections

Answer 20

2-dimensional projections of chiral molecules that are useful when evaluating stereochemistry

Question 21

In Fischer projections, groups on the right and left are by convention ______. Groups on the top and bottom are by convention ______.

Answer 21

in front, behind

Question 22

Enantiomers have ________ physical and chemical properties in achiral environments but ______ properties in ______ environments. They also have _______ properties in the presence of chiral reagents and enzymes as chiral catalysts.

Answer 22

identical, different, different

Question 23

Diastereomers have ______ physical and chemical properties even in achiral environments.

Answer 23

different