Heat evolved upon catalytic hydrogenation (∆ Ho)
A MEASURE OF ALKENE STABILITY
ALKENE
C4H8
H2/Pd-C
ALKANE
C4H10
EXOTHERMIC
ENERGY
(-) 28.3
kcal/mol
(-) 30.3
kcal/mol
(-) 27.4
kcal/mol
Best to compare compounds that react
to form same alkane
Trans > Cis > Geminal
1
SUMMARY OF ALKENE CHEMISTRY
(illustrated with 1-methyl cyclopent-1-ene to emphasize transformation stereochemistry)
OH
HO
SYN
O
O
Os
H 2O/H+
mCPBA
ANTI
H 2O/H+
SYN
OH
Br
O
O
HO
HBr
OsO4
OH
O
O2
DMS
Br2
BH3
H 2/Pd-C
SYN
SYN
SYN
O
H
ANTI
O
BH2
H
H
Br
Br
Br
H 2O2
NaOH
H
SYN
OH
H
POLYOL NATURAL PRODUCTS
O
OH
OH
OH
HO
OH
OH
O
OH
O
O
HO
O
O
HO
O
OH
n
CELLULOSE
O
OH
ERYTHRONOLIDE A
(ERYTHROMYCIN A)
Antibiotic
OH
OH
O
HO
OH
O
OH
OH
OH
OH
O
O
AMPHOTERICIN B
Antifungal
CO2 H
O
NH2
OH
Me
OH
2
NATURAL PRODUCTS WITH ALKENE FUNCTIONALITY
b-Pinene
g-Bisabolene
A sesquiterpene found in the essential
oils of a number of plants
Limonene
A monoterpene
com mon in citrus fruits
Cem brene
A diterpene from pine needles
O
Caryophyllene
A constituent of clove
oil
Carvone
Spearmint oil
b-Carotene (A vitamin)
A tetraterpene bright orange in
color and the precursor to the
visual pigment retinal
OH
Vitamin A (vision)
MARKOVNIKOV and ANTI-MARKOVNIKOV ADDITION TO ALKENES
R-O-O-R
R-O + HBr
2 R-O
R-OH + Br
H+
Br
Br-
Markovnikov
Br
In the dark, in the absence of
peroxides polar solvents to
promote formation of polar
intermediate.
Most substituted carbonium ion
intermediate gives most
substituted bromide product
Br
HBr
AntiMarkovnikov
Br
In the presence of peroxides
and heat or light to promote
homolytic cleavage of O-O
bond.
Most substituted radical
intermediate gives least
substituted bromide product
3
ALKENE POLYMERIZATION - SPECIAL TOPIC
STRUCTURE
POLYMER (trade name)
ethene
H 2 C CH2
polyethylene (polythene)
propene
H 2 C CH
CH3
polypropylene
MONOMER
chloroethene
(vinyl chloride)
PVC (polyvinyl chloride)
H2 C CH
Cl
acrylonitrile
H
H2 C C
tetrafluoroethene
F2C
Orlon (acrilan)
C N
CF 2
TEFLON
H
H2 C C
phenylethene
(styrene)
POLYSTYRENE
methylmethacrylate
LUCITE (Plexiglass)
OMe
O
1,1-dichloroethene
and 1-chloroethene
Random co-polymer
SARAN WRAP
H2 C CCl2
H2 C CHCl
FREE RADICAL POLYMERIZATION
INITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS
INITIATION
O
2
O
O
2
O
O O
+ 2 CO2
POLYMERIZATION
TERMINATION
n
Ph
n
Ph
4
FREE RADICAL POLYMERIZATION
INITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS
INITIATION
O
2
O
O
2
O
O O
+ 2 CO2
POLYMERIZATION
TERMINATION
n
Ph
n
Ph
CATIONIC POLYMERIZATION
INITIATION, PROPAGATION (POLYMERIZATION) and TERMINATION STEPS
INITIATION
Good monomer for cationic
polymerization..Why?
H+Cl-
What about
tetrafluoroethene?
POLYMERIZATION
TERMINATION
- H+
n
5
CHOLESTEROL BIOSYNTHESIS
Squalene
epoxidase [O2]
Squalene
O
O
Oxidosqualene
cyclase
Me
Me
Me
HO
Me
+
Me
H
Me
+
Me
Me
H
H
HO
HO
H+
H
Me
Me
5
H
H
6
H
CHOLESTEROL
O
Oxidosqualene
cyclase
Me
Me
Me
HO
Me
Me
6