Chapter 6 PDF
Chapter 6 PDF
Chapter 6 PDF
H2, PtO2
ethanol
O
H2, Pd/C
C5H11 OH CH3(CH2)16CO2H
Linoleic Acid (unsaturated fatty acid) Steric Acid (saturated fatty acid)
O
O
OCH3 H2, Pd/C
OCH3
ethanol
H2, Pd/C C
C
N N
ethanol
128
6.2: Heats of Hydrogenation -an be used to measure relative
stability of isomeric alkenes
H H H CH3
trans isomer is ~3 KJ/mol
H3C CH3 H3C H more stable than the
cis-2-butene trans-2-butene cis isomer
ΔH°combustion : -2710 KJ/mol -2707 KJ/mol
H H H CH3
H2, Pd H2, Pd
CH3CH2CH2CH3
H3C CH3 H3C H
cis-2-butene trans-2-butene
129
H H
monosubstituted
125 - 126
H3C H
H H
117 - 119
H3C CH3
H CH3
disubstituted 114 - 115
H3C H
H3C H
116 - 117
H3C H
H3C H
trisubstituted 112
H3C CH3
H3C CH3
tetrasubstituted 110
H3C CH3 130
6.3: Stereochemistry of Alkene Hydrogenation
Mechanism:
H H
H2C CH2 H H H2C CH2
H2C CH2
H2
H H
H H
H H C C
C H H H
H H
C H
EtOH CH3
CH3 CH3
H H
syn addition
of H2 Not observed
131
135
~ 50% ~ 50%
expected product
H
Cl H
H3C H
H3C C H H-Cl H3C C H
+ H3C C H
C C C C
C C
H3C H3C H
CH3 H CH3 H H3C H
Cl H
Note that the shifting atom or group moves with its electron pair.
A MORE STABLE CARBOCATION IS FORMED. 136
6.8: Free-radical Addition of HBr to Alkenes
H
Br H
C H H-Br +
H Br
Polar mechanism
H3CH2C C H3CH2C C C H H3CH2C C C H
H H H H H
(Markovnikov addition)
none of this
H
C H H-Br Br H
+
H Br Radical mechanism
H3CH2C C H3CH2C C C H H3CH2C C C H
H peroxides H H H H
(Anti-Markovnikov addition)
(RO-OR)
none of this
H H-Br Br H H Br
C H R C C H + R C C H
R C
H
ROOR H H H H The regiochemistry of
(peroxides) none of this
R
HBr addition is reversed
Br H H Br
C H
H-Br
R C C H + R C C H
in the presence of
R C
H
ROOR R H R H peroxides.
none of this
R
R
C
C
H H-Br
Br H
+
H Br
Peroxides are radical
R C C R R C C R
R ROOR R H R H initiators - change in
none of this mechanism
R
Br H H Br
C H H-Br
H C R C C R + R C C R'
R' ROOR H H H H
137
Both products observed
138
6.9: Addition of Sulfuric Acid to Alkenes (please read)
6.10: Acid-Catalyzed Hydration of Alkenes - addition of water
(H-OH) across the π-bond of an alkene to give an alcohol;
opposite of dehydration
H3C H3C
H2SO4, H2O
C CH2 C OH
H3C
H3C H3C
139
140
6.11: Thermodynamics of Addition-Elimination Equlibria
H3C H3C
H2SO4
C CH2 + H2O C OH
H3C
H3C H3C
142
6.12: Hydroboration-Oxidation of Alkenes - Anti-Markovnikov
addition of H-OH; syn addition of H-OH
CH3 1) B2H6, THF H
2) H2O2, NaOH, H2O CH3
H
HO
6.13: Stereochemistry of Hydroboration-Oxidation
6.14: Mechanism of Hydroboration-Oxidation -
Step 1: syn addition of the H2B–H bond to the same face of the
π-bond in an anti-Markovnikov sense; step 2: oxidation of the
B–C bond by basic H2O2 to a C–OH bond, with retention of
stereochemistry
143
alkene 1,2-dihalide
not observed
Br
CH3 CH3
Br2
Br
H
144
6.17: Mechanism of Halogen Addition to Alkenes:
Halonium Ions - Bromonium ion intermediate explains the
stereochemistry of Br2 addition
145
alkene halohydrin
X2, H2O X
+ HX
OH
anti
stereochemistry
146
For unsymmterical alkenes, halohydrin formation is
Markovnikov-like in that the orientation of the addition of
X-OH can be predicted by considering carbocation stability
!+ CH3
more δ+ charge on the
Br !+ more substituted carbon
!+
HO
CH3 CH3
Br2, H2O
+ HBr
Br
H
O O
O H
OH
O
H3C O + O
H3C O
148
Stereochemistry of the epoxidation of alkenes: syn addition of
oxygen. The geometry of the alkene is preserved in the product
Groups that are trans on the alkene will end up trans on the
epoxide product. Groups that are cis on the alkene will end
up cis on the epoxide product.
H H H3CCO3H O
H H
R R R R
cis-alkene cis-epoxide
H R H3CCO3H O
H R
R H R H
trans-alkene trans-epoxide
electrical +
Ozone (O3): 3 O2 discharge
2 O3 O _
O O
mechanism
O3, CH2Cl2 O
R1 R3 -78 °C O O O O R1 R3
R1 R3 Zn
-or- O + O
R2 R4 R1 R3 R2 R4
O (H3C)2S R2 R4
R2 R4
molozonide ozonide + ZnO or (H3C)SO
1) O3
2) Zn
O + O
1) O3
2) Zn H
H + O C
H
O
1) O3
2) Zn O
H
O
150
6.21: Introduction to Organic Chemical Synthesis
Synthesis: making larger, more complex molecules out of
less complex ones using known and reliable reactions.
OH
??
151
CH3
CH3 Br
??
Br
152