Chapter 8 Notes

Stereochemistryoftheionicadditiontoanalkene

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Unformatted text preview: ion
is
formed
fastest
because
it
has
a
lower
ΔG‡.

The
transition
state
for
the
rate
 determining
step
(first
step)
resembles
a
carbocation
and
is
stabilized
by
factors
which
 stabilize
carbocations.
 Addition
of
HBr
to
2‐methylpropene
gives
only
tert‐butyl
bromide:
 Modern
Statement
of
Markovnikov’s
Rule:
In
the
ionic
addition
of
an
unsymmetrical
 reagent
to
a
double
bond,
the
positive
portion
of
the
adding
reagent
attaches
itself
to
a
 carbon
atom
of
the
double
bond
so
as
to
yield
the
more
stable
carbocation
as
an
 intermediate.

Regioselective
Reaction: 
When
a
reaction
that
can
potentially
yield
two
or
 more
constitutional
isomers
actually
produces
only
one
or
a
predominance
of
one
isomer.
 Stereochemistry
of
the
Ionic
Addition
to
an
Alkene
 Addition
of
HBr
to
1‐butene
yields
a
chiral
molecule.

A
racemic
mixture
is
produced
 because
the
intermediate
carbocation
intermediate
is
achiral.
 Addition
of
Sulfuric
Acid
to
Alkenes
 Addition
of
concentrated
sulfuric
acid
to
alkenes
leads
to
alkyl
hydrogen
sulfates
which
 are
soluble
in
the
acid.

The
addition
follows
Markovnikov’s
rule.
 The
sulfate
can
be
hydrolyzed
by
heating
with
water.

The
net
result
is
Markovnikov
 addition
of
water
to
an
alkene.
 The
reac...
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