show a synthetic pathway. hint: alkenes may be formed from alkyl halides by reaction with a strong...
TRANSCRIPT
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Show a synthetic pathwayNH2
Br
COOH
Cl
NH2
Br
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Show a synthetic pathway
HO2C
Hint: Alkenes may be formed from alkyl halides by reaction with a strong base such as NaOCH3 resulting elimination of HX.
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HO2C1)
Cl
AlCl3
2) Cl
O AlCl33) KMnO4, H2O4) H2, Pd/C5) NBS, h6) NaOCH3 in CH3OH, heat
(E2 elim of HBr)
1)
O
2)
O
HO2C3)
HO2C
HO2C
Br
4)
5)
6) workup w/ H3O+
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Fill in the blanks.
NO2
A BH2, Pd/C
CSO3, H2SO4
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StereochemistryStereochemistry refers to the
3-dimensional properties and reactions of molecules. It has its own language and terms that need to be learned in order to fully communicate and understand the concepts.
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Definitions• Stereoisomers – compounds with the same
connectivity, different arrangement in space• Enantiomers – stereoisomers that are non-
superimposible mirror images; only properties that differ are direction (+ or -) of optical rotation
• Diastereomers – stereoisomers that are not mirror images; different compounds with different physical properties
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More Definitions• Asymmetric center – sp3 carbon with 4
different groups attached• Optical activity – the ability to rotate the plane
of plane –polarized light• Chiral compound – a compound that is
optically active (an achiral compound will not rotate light)
• Polarimeter – device that measures the optical rotation of the chiral compound
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Plane-Polarized Light
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Plane-Polarized Light through an Achiral Compound
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Plane-Polarized Light through a Chiral Compound
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Polarimeter Measures Optical Rotation
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Specific Rotation, [α]
[α] = α / cl = observed rotation
c = concentration in g/mLl = length of tube in dm
Dextrorotary designated as d or (+), clockwise rotation
Levorotary designated as l or (-), counter-clockwise rotation
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Specific Rotations of some Common Organic Compounds
Compound [] # * centersPenicillin V +233.0 3Sucrose +66.5 10 Camphor +44.3 2MSG +25.5 1Cholesterol -31.3 8Morphine -132.0 5
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Chirality CenterCarbon has four different groups attached
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Enantiomers nonsuperimposible mirror images
OH
CH3HO2CH
OH
CO2HCH3
H
mirrorplane
(S)(+) lactic acid (R)(-) lactic acid
from muscle tissue from milk[] = +13.5 [] = -13.5
oo
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Absolute Configuration
1
23
4
Use Cahn, Ingold, Prelog priorities
Place the lowest priority group back (focus down C - 4 bond)
(R)
clockwise
draw arrow from 1-2-31
2 34
(S)
counterclockwise
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Assign Priority to each Group on Asymmetric Center
focus down C-4 bond
4
32
1I
ClHF
rotateI
FH
Cl
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Lactic Acid
(S) (R)
4
3 2
1
4
32
1OH
CH3 CO2HH
OH
CH3HO2CH
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C.I.P. Priorities
CH2CH2CH3 CH(CH3)2
CH2CH2OH CH2CH
O
CH2CH2CH3 CH=CH2
CO2H CH 2Cl
Low High
CH2CH2Br CH(CH3)2
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Enantiomeric Excess(Optical Purity)
actually 94.3% (+)11.4% racemic88.6% (+)
= 88.6% e.e.
x 100 123.0109.0
e.e. =
oobserved rotation = +109
from oranges
o[] = +123.0
H
from lemons
o[=
(S)-(-) Limonene (R)(+) Limonene
H
x 100 = enantiomeric excess (e.e.)rotation of pure enantiomerobserved rotation
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SSRI Efficacy depends on Stereochemistry
ON(CH3)2
F
NC
*
(+/-) Celexa(-) Lexapro
(+/-) Celexa (-) LexaproCost $17.10 per month $83.83 per month
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Art in Chemistry
Lexapro is the S enantiomer. Draw the structure of Lexapro.
ON(CH3)2
F
NC
*
(+/-) Celexa(-) Lexapro
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(R) O
F
N
NC
(S) O
F
N
NC
Art in Chemistry
Lexapro contains only the S enantiomer. Celexa is a racemic (50:50) mixture of both S and R forms.
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Biological Activity
(R)(+) Thalidomide (S)(-) Thalidomide
NN
O
O
O
O
HH
a sedative and hypnotic a teratogen
N
NO
O
O
O
H
H
In the 50’s, thalidomide was sold as a racemic mixture!
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Thalidomide was prescribed as a sedative and used against nausea and to alleviate morning sickness in pregnant women.
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Fischer Projections
Vertical bonds move away (dashed bonds)Horizontal bonds approach you (wedge bonds)
OH
CO2H
CH3
HOH
CH3HO2CH
OH
CO2H
CH3
H
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Assigning Absolute Configuration to Fischer
Projections
OH
CO2H
CH3
HOH
CO2H
CH3
HOH
CH3HO2CH
(S) (S) (S)rotate
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Rotation of the Projection 90o
Reverses Absolute Configuration
90o
90oo90
(S) (R) (S) (R)
CH3
H
OH
HO2C
CO2H
CH3
H
HO
H
OH
CO2H
CH3
OH
CO2H
CH3
H
Translation: If you rotate the Fisher projection 90o you are drawing the opposite enantiomer!
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Determine the stereochemistry at all chiral centers.
COOH
HHO
OH
NH2
O
HO
O
O-
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(S)(S)
(R) (S)
(Z)
(R)
COOH
HHO
OH
NH2
(S)
O
HO
O
O-
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H3C H
(S)
OH
(1)
(R)
(R)(2)
(R)
(Z)(3)
(R) (S)
OH
(4)
(5)
Br
Br
O
(S) (R)HH3C
CH3CF3
HH3CH2C
(6)
(7)
(R) (S)
(8)
(R) (S)
(9)
(10)
O
CH3
HCl
CHO(R)
OHH(S)
HHO
OH
O
(R)
(S)
HOHO
OHOH
(S)
(S)
OH
Front C: RBack C: R
(7) Should be R, R, S, R from C-1;5th chiral center not included.
1
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DiastereomersStereoisomers That Are Not Mirror Images
3 3 22
opposite stereochemistry at C3
same stereochemistry at C2 (S)
CO2H
OHH
Br HCO2H
OHH
BrH(2S,3S) (2S,3R)
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Fischer Projections with 2 Chiral Centers
CO2H
CH3
H OH
Br H H Br
H OH
CO2H
CH3
(2S,3S) (2S,3R)
2
3
2
3
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2 Chiral Centers4 Stereoisomers
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Identical, Enantiomers or Diastereomers?
H
H
CH3
CH3
&CH3
CH3
H
H CC
a)
CH2CH3
CH3
H
H
Br
Br
CH2CH3
CH3&
b)
OH
HO
NH2
NH2
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Identical, Enantiomers or Diastereomers?
H
H
CH3
CH3
&CH3
CH3
H
H CC
a)
CH2CH3
CH3
H
H
Br
Br
CH2CH3
CH3&
b)
OH
HO
NH2
NH2
S-2-Bromobutane S-2-Bromobutane
(2R,3S)-3-aminobutan-2-ol(2R,3S)-3-aminobutan-2-ol
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Tartaric AcidsCO2H
CO2H
H OH
HO H H OH
HO H
CO2H
CO2H
CO2H
CO2H
H OH
H OH HO H
HO H
CO2H
CO2H
R,R S,S
R,S S,R
Solve one structure first.Make sure you do itcorrectly!
Use it as reference for others.
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Racemic Mixture
o
(g/mL) 1.7598 1.7598 1.7723
m.p. C 168-170 168-170 210-212
[] (degrees) - 12 + 12 0
(R,R) Tartaric acid (S,S) Tartaric Acid (+/-) Tartaric acid
Racemic Mixture (Racemate): 50/50 mixture of enantiomers
CO2H
CO2H
H OH
HO H H OH
HO H
CO2H
CO2H
R,R S,S
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Meso CompoundInternal Plane of Symmetry
Optically Inactive
orotate 180
superimposible
CO2H
CO2H
H OH
H OH HO H
HO H
CO2H
CO2H
R,S S,R
mirror plane
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2,3,4-trichlorohexaneHow many stereoisomers?
Cl
Cl
Cl3 asymmetric centers
8 stereoisomers
* **
2n, n= # asymmetric centers (3)
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n = 3; 2n = 8
CH3
CH2CH3
H Cl
Cl HH Cl Cl H
H Cl
Cl HCH3
CH2CH3
CH3
CH2CH3
Cl H
H Cl
H Cl Cl H
Cl H
H Cl
CH3
CH2CH3
H Cl
H Cl
H Cl
CH3
CH2CH3
Cl H
Cl H
Cl H
CH3
CH2CH3
Cl H
H Cl
H Cl
CH3
CH2CH3
H Cl
Cl H
Cl H
CH3
CH2CH3
S
S
R
RR
S
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A CarbohydrateCHO
CH2OH
H OH
HO H
H OH
H OH
(+) D-Glucose
R
S
R
R
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Internal Planes of Symmetry
CH3CH3
CH3CH3
CH3CH3
CH3 CH3
Both are Meso
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Asymmetric Centers on Rings
Br
Br
Br
Br
1(R),2(S) cis 1,2-dibromocyclohexane
nonsuperimposible but A flips into B
A B
BrBr
Meso
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Reactions that Generate Chirality Centers
Hydrogenation, syn
CH3CH3
CH2CH3CH2CH3
H2, Pt/C
CH2CH3 CH2CH3CH3CH3
HH
CH2CH3
CH2CH3
H CH3
H CH3
product is meso
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BrominationTrans is formed exclusively
No Meso is formed (cis)
racemic mixture
S SR RBr BrBr Br
Br2
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Bromonium Ion is Opened Equally from Both Sides
Br2
Br Br Br BrR R S S
racemic mixture
Br
Br
Br
Br
Br Br + -
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trans alkene + anti addition = MESO
CH2CH3
CH2CH3 H
H
Br2
CH2CH3
CH2CH3
HH
Br
Br
Br Br
CH2CH3CH2CH3HH
meso
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cis Alkene + anti addition = racemic mixture
H
CH2CH3 CH2CH3
H
Br2
Br Br
CH2CH3CH2CH3 H
HR R
CH2CH3
CH2CH3
H
H
Br
Br
CH2CH3CH2CH3 H
H
Br BrS S
Br
H HCH2CH3CH2CH3
Br
Br
BrH
H
CH2CH3
CH2CH3
a b
a b
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Brominations Often Generate Asymmetric Centers
Br2
R RS S
racemic mixture
CH3CH3
H H
CH3CH3
Br BrH H
CH3CH3
Br BrH H
CH3
CH3 H
H CH3
CH3 HH
Br
Br
CH3CH3
Br BrH H
S Rmeso
Br2
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Asymmetric Center is Generated Racemic Mixture Formed
H-Br
HH
Br
Br
a)
b)
Br
H
a) Br
H
b)(R) (S)
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Asymmetric Induction
PPh2
PPh2
RuCl2
CH3
OHH2
Ru(BINAP)Cl2
CH3H
OH
96% e.e.
Noyori and Knowles shared Nobel Prize in Chemistry, 2001
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Preparation of (L)-Dopafor Treatment of Parkinson’s
HO
HO
CH2CCO2H
NH2
H
l-(-) Dopa
HO
HO
CH2CH2NH2
Dopaminecannot cross blood-brain
barrier
C=CNH2
CO2HH
HO
HO
H2Rh(DIOP)Cl2
enz.
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Relevance of Stereochemistry
(S,S)(R,S)useful decongenstants
d-pseudoephedrine and l-ephedrine
4 stereoisomers
**
2 asymmetric centers
EPHEDRA from Ma Huong
NHCH3
CH3
OH
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One-step synthesisPseudophed
*
d-(S)- "Meth"l-(R) - Vicks
(methamphetamine)"desoxyephedrine"NHCH3
CH3
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-(p-isobutylphenyl)propionic acid
CH3 CO2HH
(S)(+) ibuprofen (R)(-) ibuprofen
CH3HO2C
H
anti-inflammatory 80-90% metabolized to (S)(+)
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How Sweet it is!
Sucrose
O
HOOH
O
CH2OH
OCH2OH
CH2OH
HO
HO
OH
Sucralose or Splenda
O
Cl
HOOH
O
CH2OH
OCH2Cl
CH2Cl
HO
HO
Sucralose is 600 times sweeter and does not get metabolized.
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Sildenafil (Viagra) and Caffeine
NN
NN
CH3
H
O
CH3CH2O
SN
NCH3
O
O
NN
N
N
CH3
O
O
CH3
CH3
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Radiosensitizer of Choice Until 2004
Okadaic acid17 asymmetric centers
O
OH
HOOC
OH
OH
O
OH
HO
OH
HOH
OO
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How is each Cpd related to X?
H3C
CH3CH2CH3
H
HHO
HO H
CH3
CH3
CH2CH3H
OH OH OH
H3C
OHCH2CH3
H
HH3C
H3C
CH2CH3OH
H
HH3C
CH2CH3
CH3
HH3C
OHH
CH2CH3
CH3
CH3H
OHH
H
CH2CH3
OHH3C
HH3C
Cpd X
B C
E F
G H I
A
D
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(R)
(R)
H3C
CH3CH2CH3
H
HHO
HO H
CH3
CH3
CH2CH3H
(S) (S)
OH
(S) (R)
OH
(S) (S)
OH
(S)
(R)
H3C
OHCH2CH3
H
HH3C
(R)
(S)
H3C
CH2CH3OH
H
HH3C
CH2CH3(R)
(R)
CH3
HH3C
OHH
CH2CH3(S)
(R)
CH3
CH3H
OHH
H(R)
(S)
CH2CH3
OHH3C
HH3C
Cpd X
B C
E F
G H I
A
D
Front: RBack: R
Enantiomers:A, C
Diastereomers:B, E, F, H, I
Identical:D, G