Chapter 5 Flashcards
(28 cards)
Chiral?
non superimposable mirror image, 4 different groups on a carbon = stereocenter
Amylose and cellulose are examples of what?
chirality
enantiomers
Why is cellulose not soluble in water?
OH groups are not available for H bonding (equatorial), they are involved in other bonds to other cellulose strands
Why is amylose soluble in water?
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
0 Stereocenters =?
1 Stereocenter =?
2+ Stereocenters =?
- usually achiral
- always chiral
- chiral if no symmetry, achiral if symmetrical
What is the difference between the R and S conformations of Thalidomide?
R- treats morning sickness, sleeping pill
S- teratogen= birth defects
it is chiral
What is Paclitaxel (Taxol)? Why is it controversial?
Bark from Pacific Yew tree and is used as an anticancer compound. When the bark is removed, the tree dies
What is the solution to the Taxol problem?
Deacetylbaccatin is a Himalayan Yew tree which can produce Taxol through semisynthesis and the tree doesnt die. Taxol disrupts cell division
R conformation?
rectus, right, clockwise
S conformation?
sinister, left, counter clockwise
How do you assign priority for R and S conformation? How are double bonds counted?
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
How do you figure out the number of possible stereoisomers?
2^n
n= number of stereocenters
How do enantiomers differ in R/S arrangements? Diastereomers?
e- exactly opposite
d- one the same, one different
What are diastereomers?
stereoisomers that are not enantiomers, must have 2 or more stereocenters
What is a meso compound?
achiral compound that contains stereocenters, has a plane of symmetry
What physical properties do enantiomers differ from each other?
- rotation of plane polarized light
- interact differently with other chiral molecules
everything else is the same
Optically active?
chiral molecule that rotates plane polarized light
Optically pure?
not 1:1 ratio of enantiomers
Racemic mixture?
1:1 ratio of enantiomers that does not rotate plane polarized light
Percent enantiomeric excess?
percent of major enantiomer minus percent minor enantiomer
How do melting and boiling points differ between enantiomers?
they are the same, sometimes are different with racemic mixtures, cannot separate them
How do physical properties differ between diastereomers?
they are very different, can separate them
Who is the father of chirality?
Louis Pasteur (1848), found that mirror image crystals rotate plane polarized light
What are S and R Caravone?
S- caraway seeds
R- spearmint
they are enantiomers of each other, separately they smell different and rotate plane polarized light
