Lecture15notes

Lecture15notes - 10/2/09
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Unformatted text preview: 10/2/09
 Radicals
in
biological
systems
 H O O O + RH + R R O H O + 2RH O H Hydroquinone Quinone CH2OH H OH O HO O CH3 H HO OH H3C CH3 O Vitamin C (Ascorbic acid) Vitamin E (α-tocopherol) •  •  Radicals
are
very
reactive
and
can
cause
significant
damage
to
biological
systems
 To
prevent
damage
by
free
radicals
biological
systems
have
molecules
that
can
act
 as
radical
inhibitors
like
hydroquinones,
vitamin
C,
and
vitamin
E
 Hydrogenation
 C
 H
 3
 2
 H
 P
t
/
C
 C
 H
 H
 3
 +
 H
 With
the
help
of
metal
catalysts,
H2
adds
to
the
double
 bond.
 1
 10/2/09
 Hydrogenation
 The
catalyst
is
necessary,
since
the
H‐H
bond
is
too
strong.
 H‐H

bond
energy:
435
kJ/mol
 Hydrogenation
 The
number
of
C‐H
bonds
increases:
 
 cyclohexene:
10
bonds
 
 cyclohexane:
12
bonds
 We
do
a
reduction
reaction
 2
 10/2/09
 Hydrogenation
 C
 H
 3
 2
 H
 P
t
/
C
 C
 H
 H
 3
 +
 H
 The
mechanism
of
the
hydrogenation
is
as
follows:
 1.  Absorption
of
hydrogen
on
the
metal
surface.

 
 H2
molecules
are
broken
down
into
atoms.
 Hydrogenation
 C
 H
 3
 2
 H
 P
t
/
C
 C
 H
 H
 3
 +
 H
 The
mechanism
of
the
hydrogenation
is
as
 follows:
 1.  Absorption
of
hydrogen
on
the
metal
surface
 2. 
Alkene
approaches
surface
 3
 10/2/09
 Hydrogenation
 C
 H
 3
 2
 H
 P
t
/
C
 C
 H
 H
 3
 +
 H
 The
mechanism
of
the
hydrogenation
is
as
follows:
 1.  Absorption
of
hydrogen
on
the
metal
surface
 3.  Alkene
approaches
surface
 3. 
p
bonds
are
replaced
by
C‐H
bonds,
rehybridization
 C
 H
 Hydrogenation
 3
 2
 P
t
/
C
 C
 H
 H
 H
 3
 +
 H
 The
mechanism
of
the
hydrogenation
is
as
follows:
 1.  Absorption
of
hydrogen
on
the
metal
surface
 3.  Alkene
approaches
surface
 5.  p
bonds
are
replaced
by
C‐H
bonds,
rehybridization
 4. 
Addition
of
hydrogen
is
strictly
syn;
 both
H
atoms
come
from
one
side.
 4
 ...
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