CHAPTER 8: ADDITION REACTIONS OF ALKENES
Addition is favored at lower temperatures and elimination is favored at higher temperatures.
Name of Reaction Reaction Example Reagent Product Formation
Mechanism
Hydrohalogenation: - HX HX:
Addition of H and - HBr, ROOR X is attached to the
- Mark X across a pi more substituted
Unsymmetrical alkenes, bond where X is side.
halogen at the more the halogen. (Rearrangement can
substituted position occur to produce a
- Anti-Mark more stable
Presence of peroxides, carbocation.)
addition to less
substituted.
A new chiral center
formed, two
enantiomers (R or
S).
HBR, ROOR:
Br is attached to the
less substituted side.
Acid-Catalyzed H3O+ Both reagents add
Hydration an OH group on the
(Mark OH) more substituted
side.
The acid-catalyzed
addition of water to
,alkenes yields alcohol.
The addition is stepwise
with a carbocation
intermediate and
rearrangements often
occur.
Dilute acid favors the
formation of alcohol,
concentrated aid
favors the alkene.
Form a new chiral
center, racemic
mixture of
enantiomers.
Oxymercuration-demerc 1) Hg(OAc)2,
uration H2O
(Mark OH) 2) NaBH4
The mercury-catalyzed
addition of water to
alkenes yields alcohol.
The addition is stepwise
with a mercurinium ion
intermediate and
rearrangements do not
occur. This follows the
Mark rule.
Hydroboration-oxidation 1) BH3 THF Adds OH on the
(Anti Mark of OH) 2) H2O2, NaOH antimark side. It is on
Syn Addition a dash and the CH3
is on a wedge along
Stepwise reaction with H .
involving a borane
intermediate. Reaction
proceeds via syn
addition. No chiral center: no
H and BH2 are stereochemistry, no
simultaneously added enantiomers.
across the pi bond of the
alkene. One chiral center:
, The hydrogen bonds to both enantiomers
the most stable obtained because
carbocation and the syn addition can take
broron to the anti-mark place on either face
position. The H2O2, of the alkene.
NaOH adds the OH to
the anti mark and the H Two chiral centers:
on the mark position. two enantiomers with
syn addition even
though four products
are obtained (the
other two trans).
Hydrogenation Heterogeneous Reduced to single
Syn Addition Catalyst: bond.
No chiral center.
H2/Pt, Pd, Ni
The reaction of alkene (H2 in presence of
with hydrogen gas in the metal catalyst)
presence of some metal
surface to create a syn Homogeneous
addition. Only syn is Catalyst:
observed. No
H2/Wilkinson’s
enantiomer (same
compound). Catalyst
Stereochemical
outcome depends on
the number of chiral
atoms formed in the
process.
Only one product,
meso compound
and does not have
an enantiomer.
Halogenation X2 (Br2, Cl2) Trans Addition of Br.
Anti Addition One on a wedge and
the other on a dash.
Halo: Halogen
Enantiomers,
racemic mixture
Addition is favored at lower temperatures and elimination is favored at higher temperatures.
Name of Reaction Reaction Example Reagent Product Formation
Mechanism
Hydrohalogenation: - HX HX:
Addition of H and - HBr, ROOR X is attached to the
- Mark X across a pi more substituted
Unsymmetrical alkenes, bond where X is side.
halogen at the more the halogen. (Rearrangement can
substituted position occur to produce a
- Anti-Mark more stable
Presence of peroxides, carbocation.)
addition to less
substituted.
A new chiral center
formed, two
enantiomers (R or
S).
HBR, ROOR:
Br is attached to the
less substituted side.
Acid-Catalyzed H3O+ Both reagents add
Hydration an OH group on the
(Mark OH) more substituted
side.
The acid-catalyzed
addition of water to
,alkenes yields alcohol.
The addition is stepwise
with a carbocation
intermediate and
rearrangements often
occur.
Dilute acid favors the
formation of alcohol,
concentrated aid
favors the alkene.
Form a new chiral
center, racemic
mixture of
enantiomers.
Oxymercuration-demerc 1) Hg(OAc)2,
uration H2O
(Mark OH) 2) NaBH4
The mercury-catalyzed
addition of water to
alkenes yields alcohol.
The addition is stepwise
with a mercurinium ion
intermediate and
rearrangements do not
occur. This follows the
Mark rule.
Hydroboration-oxidation 1) BH3 THF Adds OH on the
(Anti Mark of OH) 2) H2O2, NaOH antimark side. It is on
Syn Addition a dash and the CH3
is on a wedge along
Stepwise reaction with H .
involving a borane
intermediate. Reaction
proceeds via syn
addition. No chiral center: no
H and BH2 are stereochemistry, no
simultaneously added enantiomers.
across the pi bond of the
alkene. One chiral center:
, The hydrogen bonds to both enantiomers
the most stable obtained because
carbocation and the syn addition can take
broron to the anti-mark place on either face
position. The H2O2, of the alkene.
NaOH adds the OH to
the anti mark and the H Two chiral centers:
on the mark position. two enantiomers with
syn addition even
though four products
are obtained (the
other two trans).
Hydrogenation Heterogeneous Reduced to single
Syn Addition Catalyst: bond.
No chiral center.
H2/Pt, Pd, Ni
The reaction of alkene (H2 in presence of
with hydrogen gas in the metal catalyst)
presence of some metal
surface to create a syn Homogeneous
addition. Only syn is Catalyst:
observed. No
H2/Wilkinson’s
enantiomer (same
compound). Catalyst
Stereochemical
outcome depends on
the number of chiral
atoms formed in the
process.
Only one product,
meso compound
and does not have
an enantiomer.
Halogenation X2 (Br2, Cl2) Trans Addition of Br.
Anti Addition One on a wedge and
the other on a dash.
Halo: Halogen
Enantiomers,
racemic mixture
