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
