Chapter 8 notes

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Unformatted text preview: Chapter
8
 Alkenes
and
Alkynes
II:

 Addition
Reactions
 Introduction:
Additions
to
Alkenes
 Generally
the
reaction
is
exothermic
because
one
π
and
one
σ
bond
are
converted
to
two
σ
 bonds.
 The
π
electrons
of
the
double
bond
are
loosely
held
and
are
a
source
of
electron
density,
 i.e.
they
are
nucleophilic.

Alkenes
react
with
electrophiles
such
as
H+
from
a
hydrogen
 halide
to
form
a
carbocation.
 The
carbocation
produced
is
an
electrophile.

It
can
react
with
a
nucleophile
such
as
a
 halide.
 In
addition
reactions
the
alkene
changes
from
a
nucleophile
in
the
first
step
to
an
 electrophile
in
the
second.
 Addition
of
Hydrogen
Halides
to
Alkenes:
 Markovnikov’s
Rule
 Addition
of
HBr
to
propene
occurs
to
give
2‐bromopropane
as
the
major
product.
 Markovnikov’s
Rule
(Original):
addition
of
HX
to
an
alkene
proceeds
so
that
the
hydrogen
 atom
adds
to
the
carbon
that
already
has
the
most
hydrogen
atoms.
 Mechanism
for
Hydrogen
Halide
Addition
to
an
 Alkene
 The
reaction
has
a
highly
endergonic
first
step
(rate
determining)
and
a
highly
 exergonic
second
step.
 Theoretical
Explanation
of
Markovnikov’s
Rule
 The
product
with
the
more
stable
carbocation
intermediate
predominates.

The
most
stable
 carbocat...
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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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