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BÀI GIẢNG ORGANIC CHEMISTRY chapter5

ORGANIC CHEMISTRY
Dr Nam T. S. Phan
Faculty of Chemical Engineering
HCMC University of Technology
Office: room 211, B2 Building
Phone: 38647256 ext. 5681
Email: ptsnam@hcmut.edu.vn
1


Chapter 5:

ALKENES

An sp2
hybridized
carbon

2



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
3


Determine the parent
hydrocarbon – the
longest continuous
carbon chain containing
the C=C

4


Note: Alkenes can have geometric isomers

5


PREPARATION OF ALKENES
Dehydrations of alcohols

Acid

isomerization
6


isomerization

7


Eliminations of alkyl halides

Base

8


Alkyne hydrogenations
Pd/CaCO3 + Pb(OAc)2 / quinoline

9


REACTIONS OF ALKENES
Additions of hydrogen halides (AE)

More stable

Markovnikov’s rule

10


Carbocation rearrangement

More stable

11


More stable

12


Stereochemistry

Racemic mixture

13


Already has 1 asymmetric carbon
14


2 asymmetric carbons are created

15


Additions of hydrogen bromide (AR)
Electrophilic addition (AE)

Radical addition (AR) – only for HBr

16


Reaction
mechanism:

17


Additions of halogens

18


Major
addition
product –
NOT a
dihalide

19


Stereochemistry

20


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Stereochemistry
2 asymmetric carbons are created

Trans-2-butene Æ meso compound

22


Additions of water – hydration reactions
Water is too weakly acidic to allow the hydrogen to act
as an electrophile

Markovnikov’s rule

H2SO4, H3PO4…
23


Reaction
mechanism:

Carbocation
rearrangement
might occur

24


Alcohols by oxymercuration-reduction

Markovnikov’s rule
No carbocation formation, no rearrangement

25


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