Chemistry > Hydrocarbons > 5.0 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
5.1 Substitution reactions of Alkanes
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
(A) Halogenation
It involves the replacement of 10, 20 & 30 H of alkanes by halogen (F, Cl, Br, I)
For a given type of abstraction of H (say 10) reactivity of halogen is in order:
${F_2} > {\text{ }}C{l_2} > {\text{ }}B{r_2} > {\text{ }}{I_2}$
For a given halogen, abstraction of 10, 20 and 30 H’s is in order:
${1^0} < {\text{ }}{2^0} < {\text{ }}{3^0}$
For chlorination, reactivity of ${1^0},{\text{ }}{2^0},{\text{ }}{3^0}$ H’s is in ratio:
$1{\text{ }}:{\text{ }}2{\text{ }}:{\text{ }}3{\text{ }}:{\text{ }}:{\text{ }}1{\text{ }}:{\text{ }}3.8{\text{ }}:{\text{ }}5$
$$\Delta {\text{ }} = {\text{ }}105{\text{ }}kcal{\text{ }}mo{l^{ - 1}}$$
$$\Delta {\text{ }} = {\text{ }}100{\text{ }}kcal{\text{ }}mo{l^{ - 1}}$$
$$\Delta {\text{ }} = {\text{ }}96{\text{ }}kcal{\text{ }}mo{l^{ - 1}}$$
$$\Delta {\text{ }} = {\text{ }}93{\text{ }}kcal{\text{ }}mo{l^{ - 1}}$$
Bond energy of extraction of ${1^0}H{\text{ }} > {\text{ }}{2^0}H{\text{ }} > {\text{ }}{3^0}$ H, hence the reactivity order is ${1^0} < {\text{ }}{2^0} < {\text{ }}{3^0}$ H, hence, the stability order of alkyl radical free is
Mechanism
\[C{H_4} + C{l_2}\xrightarrow[{}]{{hv}}C{H_3}Cl + HCl\]
(i) Initiation:
\[C{l_2}\xrightarrow[{}]{{h\nu }}2C{l^o}\]
(ii) Propagation:
\[C{H_4} + C{l^o}\xrightarrow[{}]{{}}HCl + CH_3^o\]
\[CH_3^o + Cl_2^{}\xrightarrow[{}]{{}}C{H_3}Cl + Cl_{}^o\]
(iii) Termination:
\[CH_3^o + CH_3^o\xrightarrow[{}]{{}}C{H_3} - CH_3^{}\]
\[Cl_{}^o + Cl_{}^o\xrightarrow[{}]{{}}C{l_2}\]
\[CH_3^o + C_{}^o\xrightarrow[{}]{{}}C{H_3} - Cl\]
Based on relative reactivity of different types of ${H_2}$ percentage of each isomer in the product mixture can be calculated. Consider the case of n – butane.
Relative amount = No. of equivalent hydrogen $ \times $ reactivity
Total amount = 21.2
\[\% {\text{ }}of{\text{ }}A{\text{ }} = \xrightarrow[{21.2}]{{6.0}} \times 100 = 28.3\]
\[\% {\text{ }}of{\text{ }}B{\text{ }} = \xrightarrow[{21.2}]{{15.2.}} \times 100 = 71.7\]
Bromine is less reactive with alkanes in comparison to chlorine, but bromine is more selective in the site of attack when it does react
(B) Nitration
Replacement of H by a nitro group, $ - N{O_2},$ is called nitration.
(C) Sulphonation
Replacement of H by a sulphonic acid group, SO3H is called sulphonation. Oleum is used as a source of $( - S{O_3}H).$
\[{RH{\text{ }} + {\text{ }}{H_2}S{O_4}/S{O_3}\xrightarrow[{}]{}RS{O_3}H{\text{ }} + {\text{ }}{H_2}S{O_4}}\]
\[{{{\left( {C{H_3}} \right)}_3}CH{\text{ }} + {\text{ }}{H_2}S{O_4}/S{O_3}\xrightarrow{{}}{{\left( {C{H_3}} \right)}_3}CS{O_3}H{\text{ }} + {\text{ }}{H_2}S{O_4}}\]
