Chapter 5

Question 1

Chiral?

Answer 1

non superimposable mirror image, 4 different groups on a carbon = stereocenter

Question 2

Amylose and cellulose are examples of what?

Answer 2

chirality

enantiomers

Question 3

Why is cellulose not soluble in water?

Answer 3

OH groups are not available for H bonding (equatorial), they are involved in other bonds to other cellulose strands

Question 4

Why is amylose soluble in water?

Answer 4

more OH groups are available for H bonding, helical structure prevents other amylose from binding

-it is used as a source of energy, more compact

Question 5

0 Stereocenters =?
1 Stereocenter =?
2+ Stereocenters =?

Answer 5

• usually achiral
• always chiral
• chiral if no symmetry, achiral if symmetrical

Question 6

What is the difference between the R and S conformations of Thalidomide?

Answer 6

R- treats morning sickness, sleeping pill

S- teratogen= birth defects

it is chiral

Question 7

What is Paclitaxel (Taxol)? Why is it controversial?

Answer 7

Bark from Pacific Yew tree and is used as an anticancer compound. When the bark is removed, the tree dies

Question 8

What is the solution to the Taxol problem?

Answer 8

Deacetylbaccatin is a Himalayan Yew tree which can produce Taxol through semisynthesis and the tree doesnt die. Taxol disrupts cell division

Question 9

R conformation?

Answer 9

rectus, right, clockwise

Question 10

S conformation?

Answer 10

sinister, left, counter clockwise

Question 11

How do you assign priority for R and S conformation? How are double bonds counted?

Answer 11

atomic number, the first point of difference

a double bond to a C is counted as two C’s

lowest priority needs to always be pointed back

Question 12

How do you figure out the number of possible stereoisomers?

Answer 12

2^n

n= number of stereocenters

Question 13

How do enantiomers differ in R/S arrangements? Diastereomers?

Answer 13

e- exactly opposite

d- one the same, one different

Question 14

What are diastereomers?

Answer 14

stereoisomers that are not enantiomers, must have 2 or more stereocenters

Question 15

What is a meso compound?

Answer 15

achiral compound that contains stereocenters, has a plane of symmetry

Question 16

What physical properties do enantiomers differ from each other?

Answer 16

1. rotation of plane polarized light
2. interact differently with other chiral molecules

everything else is the same

Question 17

Optically active?

Answer 17

chiral molecule that rotates plane polarized light

Question 18

Optically pure?

Answer 18

not 1:1 ratio of enantiomers

Question 19

Racemic mixture?

Answer 19

1:1 ratio of enantiomers that does not rotate plane polarized light

Question 20

Percent enantiomeric excess?

Answer 20

percent of major enantiomer minus percent minor enantiomer

Question 21

How do melting and boiling points differ between enantiomers?

Answer 21

they are the same, sometimes are different with racemic mixtures, cannot separate them

Question 22

How do physical properties differ between diastereomers?

Answer 22

they are very different, can separate them

Question 23

Who is the father of chirality?

Answer 23

Louis Pasteur (1848), found that mirror image crystals rotate plane polarized light

Question 24

What are S and R Caravone?

Answer 24

S- caraway seeds
R- spearmint

they are enantiomers of each other, separately they smell different and rotate plane polarized light

Question 25

Optically inactive?

Answer 25

• achiral compound with no SC’s
• meso compound
• racemic mixture

Question 26

Achiral?

Answer 26

compound and its mirror image are superimposable

Question 27

d+?

Answer 27

dextrarotary, rotates polarized light clockwise

Question 28

l-?

Answer 28

levorotary, rotates polarized light counterclockwise