Chapter 5 Flashcards
Stereochemistry is the study of _______ structure of molecules
3D
_______: any atom at which the interchange of 2 groups gives a stereoisomer
Stereocenter
Chiral Centers must have __ different groups
4
Corollary: if 2 groups are the same. the molecule is ________
achiral
_______: non-superimposable mirror images
enantiomers
What are the 3 situations where you know that a normal chiral center is not possible?
1) CH2
2) CH3
3) Double or triple bond
Molecules that have chiral centers and an internal plane of symmetry are _______ and called _______
achiral
meso compounds
When assigning (R) and (S) configurations (according to Chan-Ingold-Prelog):
1) number atoms attached to the chiral center, the highest atomic number has _______ priority
2) if tied, look at _______ point of difference
3) double and triple bonds are treated as if each is constructed from _______ bonds
(Br,H,H)>(O,O,H)
1) higher
2) first
3) single
When assigning (R) and (S) configurations (according to Chan-Ingold-Prelog):
4) orient group ___ away from you and connect 1,2,3
5) if arrow moves clockwise: _______
if arrow moves counterclockwise: ________
4) 4
5) (R)
(S)
The lowest priority group (#4) needs to be in the back. IF priority group #4 is in front, determine the absolute configuration and then _______ your answer.
flip
Polarimetry is used to distinguish between enantiomers (chiral molecules) based on their ability to rotate the _______ light with same magnitude, but in _______ direction
plane-polarized
opposite
Compounds that rotates p/p-light are said to be _______
optically active
If p/p-light is rotated clockwise, it is considered to be _______ or (__)
dextrorotatory (d)
(+)
If p/p-light is rotated counterclockwise, it is considered to be _______ or (__)
levelrorotary (l)
(-)
Racemic mixtures (or racemate): contain _______ mixture of enantiomers with an overall rotation of __
50:50
0°
The _______, which is sometimes called enantiomeric excess, can be determined if a mixture is neither optically pure or racemic
optical purity (op)
The optical purity is the _______ in one enantiomer from the race mixture
excess
40 %(S)
40% (R)
op: 20 %(S)
What are the 2 exceptions to chiral compounds without asymmetric atoms?
1) biphenyls (staggered)
2) allenes (end C with Dif groups)
_______: stereoisomers that are not mirror images. (_______ but not _______ chiral centers inverted)
diastereoisomers
some
all
Enantiomers: _______ chemical and physical properties in achiral environment
identical
Diastereomers: _______ chemical and physical properties
different
to find the max number of stereoisomers:
2^(# of chiral centers) - (lines of symmetry)
Cis-trans isomerism on double bonds are _______
diastereomers
_______ have different physical properties, so we can separate them by ordinary means such as distillation, recrystallization, and chromatography
Diastereomers
_______ have similar physical properties, so their separation is a more difficult process. This type of separation is called _______
enantiomers
resolution
_______ Resolution: the reaction of a pure enantiomer of one compound with a racemic mixture of another compound produces a mixture of diastereomers. Separation of the diastereomers, followed by hydrolysis, gives the resolved enantiomers
chemical
_______ Resolution: the enantiomers of the racemic compound form diastereomeric complexes with the chiral material on the column packing. One of the enantiomers binds more tightly than the other, so it moves slowly through the column
chromatographic
A chiral atom doesn’t necessarily have to be a carbon. it can also be _______, _______, _______
N
P
S
IF a lone pair is on a N, it is _______ @ room temp because of rapid inversion
achiral
