Chemistry > Hydrocarbons > 10.0 Mechanism Of Some Important Reaction Of Alkenes
Hydrocarbons
1.0 Introduction
2.0 Alkanes
3.0 Methods of Preparation Alkanes
4.0 Physical Proparties
5.0 Chemical Properties
6.0 Alkenes
7.0 Methods of Preparation Alkenes
7.1 Dehydrohalgoenation
7.2 Dehydration of Alcohols
7.3 Dehalogenation
7.4 Thermal elimination reaction
7.5 By partial reduction of alkynes:
7.6 Wittig Reaction
7.7 Kolbe hydrocarbon synthesis
8.0 Physical Proparties
9.0 Chemical Properties
10.0 Mechanism Of Some Important Reaction Of Alkenes
10.1 Mechanism of halogen addition
10.2 Mechanism of halohydrin formation
10.3 Syn - hydroxylation
10.4 Oxidation reactions of alkenes
11.0 Alkynes
12.0 Methods of Preparation Alkynes
12.1 Industrial source
12.2 Kolbe’s method
12.3 Dehydrohalogenation of 1, 2 – dihalides
12.4 Dehydrohalogenation of 1, 1 – dihalides
12.5 Dehalogenation of tetrahalides or trihalides
12.6 Alkylation of acetylene and terminal alkynes
13.0 Physical Properties
14.0 Chemical Properteis
14.1 Electrophilic addition reactions
14.2 Acidity of Alkynes
14.3 Aromatic Hydrocarbons
14.4 Structure of Benzene
15.0 Modern Concept
15.1 Aromaticity in Benzene and Related Systems
15.2 Huckel’s rule or $\left( {{\bf{4n}}{\text{ }} + {\text{ }}{\bf{2}}} \right)\pi $ electron rule
16.0 Properteis
17.0 Mechanism of Electrophilic Substitution Reactions
17.1 Nitration
17.2 Friedel – Craft Alkylation
17.3 Friedel – Craft Acylation
17.4 Reactions of side chains
18.0 Toluene
19.0 Alkenyl Benzene
10.1 Mechanism of halogen addition
7.2 Dehydration of Alcohols
7.3 Dehalogenation
7.4 Thermal elimination reaction
7.5 By partial reduction of alkynes:
7.6 Wittig Reaction
7.7 Kolbe hydrocarbon synthesis
10.2 Mechanism of halohydrin formation
10.3 Syn - hydroxylation
10.4 Oxidation reactions of alkenes
12.2 Kolbe’s method
12.3 Dehydrohalogenation of 1, 2 – dihalides
12.4 Dehydrohalogenation of 1, 1 – dihalides
12.5 Dehalogenation of tetrahalides or trihalides
12.6 Alkylation of acetylene and terminal alkynes
14.2 Acidity of Alkynes
14.3 Aromatic Hydrocarbons
14.4 Structure of Benzene
15.2 Huckel’s rule or $\left( {{\bf{4n}}{\text{ }} + {\text{ }}{\bf{2}}} \right)\pi $ electron rule
17.2 Friedel – Craft Alkylation
17.3 Friedel – Craft Acylation
17.4 Reactions of side chains
The mechanism proposed is an ionic mechanism.
In the first step the exposed electrons of the $\pi $- bond of the alkene attacks the halogen in the following way:
As $\pi - e's$ of the alkene approach the bromine molecules, the electrons of bromine – bromine bond drift to make bromine molecule polarised. The more distant bromine develops a partial negative charge and nearer bromine becomes partially positive. Polarization weakens the bond and cleaves it heterolytically.
In second step, one of the bromide ions predicted in step I attacks one of the carbon atoms of the bromonium ion. The nucleophilic attack results in the formation of a vicinal dibromide by opening the three – membered ring.
On reaction of cyclopentane with bromine in $CC{l_4},$ anti – addition occurs and the products of the reaction are trans – 1, 2 dibromocyclopentane enantiomers (as a race`mate)
Addition of bromine to cis – 2 – butene gives racemic form of 2, 3 – dibromobutane.
Bromine adds to trans – 2 – butene to form meso compound, thus the reaction is stereospecific in nature.
