ORGANIC CHEMISTRY
Dr Nam T. S. Phan
Faculty of Chemical Engineering
HCMC University of Technology
Office: room 211, B2 Building
Phone: 8647256 ext. 5681
Email:
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Chapter 5:
ALKENES
An sp2
hybridized
carbon
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NOMENCLATURE OF ALKENES
The IUPAC name of an alkene is obtained by replacing
the “ane” ending of the corresponding alkane with “ene”
• Ethylene is an acceptable synonym for ethene in the IUPAC
system
• Propylene, isobutylene and other common names ending in
“ylene” are NOT acceptable IUPAC names
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Determine the parent
hydrocarbon – the
longest continuous
carbon chain containing
the C=C
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Note: Alkenes can have geometric isomers
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PREPARATION OF ALKENES
Dehydrations of alcohols
Acid
isomerization
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isomerization
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Eliminations of alkyl halides
Base
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Alkyne hydrogenations
Pd/CaCO3 + Pb(OAc)2 / quinoline
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REACTIONS OF ALKENES
Additions of hydrogen halides (AE)
More stable
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Carbocation rearrangement
More stable
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More stable
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Additions of hydrogen bromide (AR)
Electrophilic addition (AE)
Radical addition (AR) – only for HBr
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Reaction
mechanism:
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Stereochemistry
Racemic mixture
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Already has 1 asymmetric carbon
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2 asymmetric carbons are created
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Additions of halogens
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Major
addition
product –
NOT a
dihalide
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Stereochemistry
2 asymmetric carbons are created
Trans-2-butene Æ meso compound
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Additions of water – hydration reactions
Water is too weakly acidic to allow the hydrogen to act
as an electrophile
Markovnikov’s rule
H2SO4, H3PO4…
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Reaction
mechanism:
Carbocation
rearrangement
might occur
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Alcohols by oxymercuration-reduction
Markovnikov’s rule
No carbocation formation, no rearrangement
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Additions of borane: hydroboration-oxidation
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Regioselectivity:
Anti-Markovnikov
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