Chemistry > Hydrocarbons > 9.0 Chemical Properties
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
9.2 Addition reactions
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
Addition of unsymmetrical reagents such as $HX,{\text{ }}HOX,{\text{ }}{H_2}O,{\text{ }}{H_2}S{O_4}$etc to unsymmetrical alkenes such as propene occurs in accordance with Markonikov’s rule which states that the negative part of the addendum (adding regent) gets attached to that carbon atom of the double bond which has least number of hydrogen atoms
Carbocations are the intermediates and the major products always results from more stable carbocations. e.g.
In presence of peroxide, the addition of HBr to unsymmetrical alkenes occurs contrary to Markovnikov’s rule. e.g.
Anti markovnikov’s addition is generally called peroxide effect or kharasch effect. In presence of peroxides, the addition of HBr to unsymmetrical alkenes occurs by a free radical mechanism.
e.g.
Initiation:
\[R - O - O - R\xrightarrow[{Homolytic\,\,fission}]{{\Delta \,\,or\,\,h\nu }}2R\mathop O\limits^ \bullet \]
\[R\mathop O\limits^ \bullet + H - Br\xrightarrow{{}}ROH + \mathop {Br}\limits^ \bullet \]
Propagation: (i)
\[C{H_3}CH = C{H_2} + \mathop {Br}\limits^ \bullet \xrightarrow{{}}C{H_3} - \mathop C\limits^ \bullet H - C{H_2}Br\]
Free radical (more stable) (ii)
\[C{H_3} - \mathop C\limits^ \bullet H - C{H_2}Br + HBr\xrightarrow{{}}C{H_3} - C{H_2} - C{H_2}Br + \mathop {Br}\limits^ \bullet \]
Termination: (i)
\[\mathop {Br}\limits^ \bullet + \mathop {Br}\limits^ \bullet \xrightarrow{{}}Br - Br\]
(ii)
Note:
Peroxide effect is not observed with other halogen acids (HF, HCl or HI) since only HBr has both steps exothermic while with HCl second propagation step involving the reaction of carbon radical with HCl is endothermic and with HI, first propagation step involving the addition of iodine radical to alkene is endothermic.
Because of the presence of double bond alkene readily undergoes electrophilic addition reactions. Some important reactions of ethene are given below:
