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Alkene Reactions & Nomenclature

This document discusses alkenes and their reactions. It begins by defining alkene nomenclature and E/Z configuration. The main reaction of alkenes is electrophilic addition. When unsymmetrical alkenes react with hydrogen halides, two isomeric products are possible according to Markonikov's rule. The mechanism involves protonation to form a carbocation followed by halide attack. Regioselectivity and stereochemistry are also discussed, along with specific details about HBr addition reactions.

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55 views21 pages

Alkene Reactions & Nomenclature

This document discusses alkenes and their reactions. It begins by defining alkene nomenclature and E/Z configuration. The main reaction of alkenes is electrophilic addition. When unsymmetrical alkenes react with hydrogen halides, two isomeric products are possible according to Markonikov's rule. The mechanism involves protonation to form a carbocation followed by halide attack. Regioselectivity and stereochemistry are also discussed, along with specific details about HBr addition reactions.

Uploaded by

Quỳnh Anh Trần
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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ALKENE

1
NOMENCLATURE OF ALKENES

2
E/Z CONFIGURATION

3
REACTIONS OF ALKENE
The most common reaction of alkenes is
electrophilic addition (AE).

sp2 carbons
-> planar geometry

4
ADDITION OF HYDROGEN HALIDES

If unsymmetrical alkenes are used, two isomeric


products are possible.

Use Markonikov’s rule to determine.


5
ADDITION OF HYDROGEN HALIDES
Markonikov’s rule: The halogen of a hydrogen halide
is attached to the carbon of the alkene bearing the
lesser number of hydrogens.

If the two carbons of the alkene have equal numbers


of hydrogens, no regioselectivity is observed.

6
MECHANISM
1st step: protonation of alkene to form carbocation

2nd step: halide reacts with the resulting carbocation

7
REGIOSELECTIVITY

8
REGIOSELECTIVITY

9
REGIOSELECTIVITY
Addition sometimes gives an unusual product.

A rearrangement has occurred.

10
REGIOSELECTIVITY

Rearrangement is favored
by the increased stability of
the rearranged ion.
11
REGIOSELECTIVITY

A rearrangement could involve a hydride shift:


migration of hydrogen with its two bonding electrons.

12
REGIOSELECTIVITY
A rearrangement could involve a methyl shift:
migration of methyl group.

13
REGIOSELECTIVITY
A rearrangement that would give a less stable
carbocation generally does not occur.

14
STEREOCHEMISTRY
Remember that the carbon of carbocation has trigonal
planar geometry.

15
STEREOCHEMISTRY
More complicated examples:

how many isomers?


16
ADDITION of HBr to ALKENES

Peroxide effect: only applied for HBr addition

17
MECHANISM OF HBr ADDITION

most important step

18
MECHANISM OF HBr ADDITION

19
REGIOSELECTIVITY IN HBr ADDITION

20
REGIOSELECTIVITY IN HBr ADDITION

To
compare
21

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