Chapter 5: Stereoisomers

Question 1

What is an isomer?

Answer 1

Molecule with the same molecular formula, and a different structure

Question 2

What is a constitutional isomer?

Answer 2

Molecule with the same molecular formula, but different connectivity

Question 3

What is a stereoisomer?

Answer 3

Molecule with a different orientation in space

Question 4

What are the types of stereoisomers?

Answer 4

1. cis and trans
2. conformations (rotating around a sigma bond)
3. mirror image isomers (enantiomers and diastereomers)

Question 5

Achiral

Answer 5

Identical (superimposable) to its mirror image

Question 6

Chiral

Answer 6

Nonsuperimposable to its mirror image

Question 7

Enantiomers

Answer 7

Each isomer of a mirror image

Question 8

Stereocenter

Answer 8

Source of chirality (carbon w 4 different substituents)

Question 9

Diastereomer

Answer 9

Nonsuperimposable non-mirror image

Question 10

Formula for number of possible stereoisomers

Answer 10

2^x (# of stereocenters)

Question 11

Something that is optically active Is …

Answer 11

Chiral

Question 12

Enantiomers have identical physical properties, such as…

Answer 12

boiling point, melting point, density

Question 13

How do we tell enantiomers apart?

Answer 13

Plane polarized light, performed by a polarimeter

Question 14

What is the specific notation for optical rotation?

Answer 14

[d]

Question 15

How do enantiomers rotate light?

Answer 15

In equal and opposite directions

Question 16

(+) Detrorotatory

Answer 16

Right/clockwise

Question 17

(-) Levoratatory

Answer 17

Left/counter clockwise

Question 18

What does optical rotation tell us?

Answer 18

How pure our sample is (optical purity)

Question 19

What is produced when no optical rotation is present?

Answer 19

50-50 mix of enantiomers; known as a racemic mix

Question 20

If one enantiomer is present, it is referred to as …

Answer 20

Enantiopure

Question 21

What is it called if enantiomer is in excess (ee)?

Answer 21

Enantiomeric Excess (xs)

Question 22

There is no correlation between optical rotation and …

Answer 22

Structure

Question 23

Rectus

Answer 23

Right or clockwise

Question 24

Sinister

Answer 24

Left or counterclockwise

Question 25

What are the rules for determining absolute configuration?

Answer 25

1. Assign priority to substituents on chiral center
2. Place lowest priority in the back
3. Draw an arrow from high to low (1-4)

Question 26

Cahn Ingold Prelog Rules (CIP)

Answer 26

1. Higher priority from higher atomic #
2. Tie? Use the first point of difference
3. Treat pi bonds as multiple bonds to the same atom

Question 27

What do enantiomers and diastereomers have in common?

Answer 27

Both are non superimposable to their mirror image

Question 28

Describe properties of enantiomers

Answer 28

-is the mirror image
-configuration changes
-R to S or S to R

Question 29

Describe properties of diastereomers

Answer 29

-not the mirror image
-only some invert and some remain constant

Question 30

Do all chiral molecules have to have a chiral center?

Answer 30

No, we need a 3-D shape that is not the same as its mirror image

Question 31

Are all molecules w chiral centers optically active?

Answer 31

No, can have some point of symmetry or plane of symmetry

Question 32

Are all molecules with a specific shape chiral?

Answer 32

No

Question 33

List some manipulation types

Answer 33

1.) Rotate: hold one thing constant and rotate other 3
2.) Flip over
3.) Turn