Chemistry > Hydrocarbons > 15.0 Modern Concept
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
15.1 Aromaticity in Benzene and Related Systems
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
After the structure of benzene was established, the term aromatic was adapted for such compounds which despite having ? bonds (unsaturation) resist addition and instead undergo substitution. The aromaticity in benzene is attributed to the six delocalized pi electrons in the coplanar carbon hexagon. When a bonding orbital is not restricted to two atoms but is spread over more than two atoms, e.g. six in benzene, such bonding orbitals are said to be delocalized. Delocalisation results in greater stability.
The modern theory of aromaticity was advanced by Eric Huckel 1931. Aromaticity is a function of electronic structure. Any polynuclear compound, heterocyclic rings or cyclic ions may be aromatic if these have a specific electronic structure. The important features of the theory are
1. Delocalization: Complete delocalization of $\pi $ electron cloud of the ring system is a necessary requirement for aromatic character.
2. Planarity: Complete delocalization of $\pi $-electron cloud is possible only if the ring is planar. This is the reason that benzene is aromatic but cyclooctatetraene is not, since the latter is not a planar molecule.
