Oxidativecleavageofalkenes

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Unformatted text preview: anti‐Markovnikov
and
syn
addition
 Addition
of
Bromine
and
Chlorine
to
Alkenes
 The
addition
produces
vicinal
dihalides.

 This
reaction
is
used
as
a
test
for
alkenes
because
the
red
color
of
the
bromine
 reagent
disappears
when
an
alkene
(or
alkyne)
is
present.

Alkanes
do
not
react
with
 bromine
in
the
dark.
 Mechanism
of
Halogen
Addition
 A
bromonium
ion
intermediate
is
formed
instead
of
the
carbocation
seen
in
other
 addition
reactions.
 Stereochemistry
of
the
Addition
of
Halogens
to
 Alkenes
 The
net
result
is
anti
addition
because
of
SN2
attack
on
the
bromonium
ion
 intermediate.

Bromide
is
the
nucleophile
and
the
bromine
of
the
bromonium
ion
is
 the
leaving
group.

When
cyclopentene
reacts
the
product
is
a
racemic
mixture
of
 trans‐1,2‐dibromocyclopentane
enantiomers.
 Stereospecific
Reactions
 A
reaction
is
stereospecific
if
a
particular
stereoisomeric
form
of
the
starting
material
 reacts
in
such
a
way
that
it
gives
a
specific
stereoisomeric
form
of
the
product.
 Example:
cis‐
and
trans‐2‐butene
give
stereoisomeric
products
when
halogenated
 Halogenation
of
double
bonds
is
stereospecific
 Halohydrin
Formation
 If
halogenation
is
carried
out
in
aqueous
solven...
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This note was uploaded on 06/19/2009 for the course CHEM 2311 taught by Professor Tyson during the Fall '07 term at Georgia Institute of Technology.

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