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Aromatic Structures and Chemistry of Benzene

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Sana Jamshaid (사나 잠셰드)

This document provides an overview of aromatic organic compounds. It begins with an introduction to the topic and a brief history of the discovery of benzene's structure by Kekulé. The document then covers the key concepts of aromaticity including planar cyclic molecules with conjugated pi bonds and Huckel's rule. Examples of aromatic compounds like benzene and heterocyclic aromatics are discussed. The final sections discuss the sources of aromatic compounds from coal and petroleum, methods of benzene synthesis, and the many applications of aromatic compounds in products like plastics, fibers, rubbers and fuels.

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Course: 0738―ORGANIC MATERIAL STRUCTURES AND CHARACTERISTICS Presenter: Sana Jamshaid
“LET US LEARN TO DREAM GENTELMAN, AND THEN PERHAPS, SHALL LEARN THE TRUTH”. (KEKULE) 2
 Introduction  Discovery of Benzene  Structure of Benzene  Classification of aromatic compounds  Criteria for aromaticity (Huckel’s Rule)  Difference between aromatic, antiaromatic, nonaromatic  Aromatic heterocyclic compound  Annulenes  Nomenclautre  Sources of aromatic compounds  Chemistry of Benzene  Stability of Benzene  Synthesis of Benzene  Physical Properties of benzene  Spectroscopic characteristics of aromatic compounds  Chemical properties of Benzene  Aromatic compounds in our daily life  Scope of aromatic compounds and its derivatives in recent research trends  Conclusion
 The term aromatic compounds was 1st used by Kekule to classify benzene & its derivatives.  Benzene and its derivatives, many of which possess fragrance/ aroma.  According to new fact, aromatic is associated with “chemical stability” rather than aroma.  So aromatic is used for series containing benzene ring.  May be called as “ Arenes and derivatives.”  Include H-carbons, ketones, aldehydes, amines, ethers etc. 4
 The word "benzene" derives historically from "gum benzoin", sometimes called "benjamin" an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia.  Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen.
Structure of Benzene KEKULE fall asleep while sitting in front of fire, dreamed about chains of atoms in form of twisting snakes. one of snake caught hold of its own tail , forming a whirling ring. KEKULE awoke , freshly inspired , spent remainder night working on his now-famous hypothesis. 6
7 • The resonance description of benzene consists of two equivalent Lewis structures, each with three double bonds that alternate with three single bonds. • The true structure of benzene is a resonance hybrid of the two Lewis structures, with the dashed lines of the hybrid indicating the position of the  bonds. • We will use one of the two Lewis structures and not the hybrid in drawing benzene. This will make it easier to keep track of the electron pairs in the  bonds (the  electrons).
A structure of benzene, containing 3 cyclic conjugated double bonds which systematically called 1,3,5- cyclohexatriene
Aromatic Structures and Chemistry of Benzene
10 Four structural criteria must be satisfied for a compound to be aromatic. The Criteria for Aromaticity [1] A molecule must be cyclic. To be aromatic, each p orbital must overlap with p orbitals on adjacent atoms.
11 [2] A molecule must be planar. All adjacent p orbitals must be aligned so that the  electron density can be delocalized. Aeromatic compound (landscape)
12 [3] A molecule must be completely conjugated. Aromatic compounds must have a p orbital on every atom.
13 [4] A molecule must satisfy Hückel’s rule, and contain a particular number of  electrons. Benzene is aromatic and especially stable because it contains 6  electrons. Cyclobutadiene is antiaromatic and especially unstable because it contains 4  electrons. Hückel's rule:
Aromatic Structures and Chemistry of Benzene
1. Aromatic—A cyclic, planar, completely conjugated compound with 4n + 2  electrons. 2. Antiaromatic—A cyclic, planar, completely conjugated compound with 4n  electrons. 3. Not aromatic (nonaromatic)—A compound that lacks one (or more) of the following requirements for aromaticity: being cyclic, planar, and completely conjugated. https://www.youtube.com/watch?v=nrRH_xYSjE4&t=138s Considering aromaticity, a compound can be classified in one of three ways:
Aromatic Structures and Chemistry of Benzene
Aromatic Heterocyclic Compounds A heterocyclic compound has hetero atom in the ring system other than carbon The heteroatom donates either one or two electrons to the  system Heteroatom donates two electronsHeteroatom donates one electron
 A six-membered heterocycle with a nitrogen atom in its ring   electron structure resembles benzene (6 electrons)  The nitrogen lone pair electrons are not part of the aromatic system (perpendicular orbital)  Is it aromatic, anti-aromatic or non-aromatic?
 A five-membered heterocycle with one nitrogen   electron system similar to that of cyclopentadienyl anion  Nitrogen atom is sp2-hybridized, and lone pair of electrons occupies a p orbital (6  electrons) 19 Is it aromatic, anti-aromatic or non-aromatic?
Furan structure Furan and Thiphene structure are similar  Are these aromatic, anti-aromatic or non-aromatic?
N N H O S
Aromatic Structures and Chemistry of Benzene
23 • Hydrocarbons containing a single ring with alternating double and single bonds are called annulenes. • Completely conjugated rings larger than benzene are also aromatic if they are planar and have 4n + 2  electrons. • To name an annulene, indicate the number of atoms in the ring in brackets and add the word annulene.
24 • [10]-Annulene has 10  electrons, which satisfies Hückel's rule, but a planar molecule would place the two H atoms inside the ring too close to each other. Thus, the ring puckers to relieve this strain. • Since [10]-annulene is not planar, the 10  electrons can’t delocalize over the entire ring and it is not aromatic.
https://www.youtube.com/watch?v=- U3tcz5anWU&t=165s
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
 Simple aromatic hydrocarbons come from two main sources: coal and petroleum.  Coal is an enormously complex mixture made up primarily of large arrays of benzene-like rings joined together.  Thermal breakdown of coal occurs when it is heated to 1000 °C in the absence of air, and a mixture of volatile products called coal tar boils off.  Fractional distillation at coal tar yields benzene, toluene, xylene (dimethylbenzene), naphthalene, and a host of other aromatic compounds.
 Benzene is a chemical that is a colourless or light yellow liquid at room temperature. It has a sweet odour and is highly flammable.  Natural sources of benzene include volcanoes and forest fires. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke.  https://www.youtube.com/watch?v=oA 75KZLzRxQ&t=116s
Aromatic Structures and Chemistry of Benzene
 With reduction of benzene diazonium chloride with sodium stannite or hypophosphorus acid.  Benzene sulphonic acid on hydrolysis with superheated steam gives benzene.  C6H5.SO3H + H2O —> C6H6 + H2SO4  Sodium benzoate is heated with soda-lime (NaOH) and when it gets decarboxylated benzene is obtained.  https://www.youtube.com/watch?v=X10VZeQmFDo
 Catalytic reforming  Toluene hydrodealkylation  Toluene disproportionation  Pyrolysis gasoline  Production from coal tar
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Rings C=C 1600-1500 (stretching) =C-H 3100-3000 (stretching), 2000-1600 (phenyl ring substitution overtones) U S overtones Double bonds /hydrocarbons
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Principle types of reactions of BENZENE: • Electrophilic Substitution reaction https://www.youtube.com/watch?v=nhpXRjoWVHU • Nucleophilic Aromatic substitution https://www.youtube.com/watch?v=NsD8Q13ryHk
Aromatic Structures and Chemistry of Benzene
USES • Important industrial solvent and precursor in the production of drugs, plastics, synthetic rubber, dyes, resins, nylon and synthetic fibers. *Aromatic hydrocarbons of commercial interest are benzene, toluene,ortho-xylene and para- xylene *e.g. The use of polystyrene foam, produced from benzene, contributes to make homes more comfortable, keeping them warm in winter and cool in summer. It also helps to reduce energy emissions and prevents leakage. * Synthetic rubbers, also derived from aromatics, gives tyres better road-hugging ability, especially on
•In production of rubbers, lubricants, dyes, detergents, drugs, and pesticides. *e.g. Cumene and phenol, for example, both produced from benzene, are used as a starting material to make aspirin and penicillin, one of the first and still one of the antibiotic agents. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke. In a refrigertor for example interior panels are most often made out of tough, corrosion-resistant plastics such as ABS or high- impact polystyrene; clear, see-through drawers and compartments are made out of polystyrene or polycarbonate. More importantly, the foamed polyurethane, derived from toluene. Most of a CD consists of an injection-molded piece of clear polycarbonate: a plastic derived from benzene, through bisphenol A and cumene.
 In clothes : acrylic fibres, polyester, nylon, luxurious fibres – linen, silk, cashmere wool – to give them more resistance all are aromatics.  Aromatics are used today in most of our sports equipment. From polyurethane footballs to nylon parachutes, from light running shoes to polyester swimwear, aromatics provide the materials.  Gas-burner, microwave oven, coffee machine, pots and pans, milk bottles and yoghurt pots, meat trays, eggs tray even the cutlery all rely on the input of the aromatics industry
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
Aromatic Structures and Chemistry of Benzene
About 35 million tonnes aromatic compounds are produced worldwide every year. They are extracted from complex mixtures obtained by the refining of oil or by distillation of coal tar, and are used to produce a range of important chemicals and polymers, including styrene, phenol, aniline, polyester and nylon which are staring material of many organically synthesised products.
Aromatic Structures and Chemistry of Benzene

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Aromatic Structures and Chemistry of Benzene

  • 1. Course: 0738―ORGANIC MATERIAL STRUCTURES AND CHARACTERISTICS Presenter: Sana Jamshaid
  • 2. “LET US LEARN TO DREAM GENTELMAN, AND THEN PERHAPS, SHALL LEARN THE TRUTH”. (KEKULE) 2
  • 3.  Introduction  Discovery of Benzene  Structure of Benzene  Classification of aromatic compounds  Criteria for aromaticity (Huckel’s Rule)  Difference between aromatic, antiaromatic, nonaromatic  Aromatic heterocyclic compound  Annulenes  Nomenclautre  Sources of aromatic compounds  Chemistry of Benzene  Stability of Benzene  Synthesis of Benzene  Physical Properties of benzene  Spectroscopic characteristics of aromatic compounds  Chemical properties of Benzene  Aromatic compounds in our daily life  Scope of aromatic compounds and its derivatives in recent research trends  Conclusion
  • 4.  The term aromatic compounds was 1st used by Kekule to classify benzene & its derivatives.  Benzene and its derivatives, many of which possess fragrance/ aroma.  According to new fact, aromatic is associated with “chemical stability” rather than aroma.  So aromatic is used for series containing benzene ring.  May be called as “ Arenes and derivatives.”  Include H-carbons, ketones, aldehydes, amines, ethers etc. 4
  • 5.  The word "benzene" derives historically from "gum benzoin", sometimes called "benjamin" an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia.  Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen.
  • 6. Structure of Benzene KEKULE fall asleep while sitting in front of fire, dreamed about chains of atoms in form of twisting snakes. one of snake caught hold of its own tail , forming a whirling ring. KEKULE awoke , freshly inspired , spent remainder night working on his now-famous hypothesis. 6
  • 7. 7 • The resonance description of benzene consists of two equivalent Lewis structures, each with three double bonds that alternate with three single bonds. • The true structure of benzene is a resonance hybrid of the two Lewis structures, with the dashed lines of the hybrid indicating the position of the  bonds. • We will use one of the two Lewis structures and not the hybrid in drawing benzene. This will make it easier to keep track of the electron pairs in the  bonds (the  electrons).
  • 8. A structure of benzene, containing 3 cyclic conjugated double bonds which systematically called 1,3,5- cyclohexatriene
  • 10. 10 Four structural criteria must be satisfied for a compound to be aromatic. The Criteria for Aromaticity [1] A molecule must be cyclic. To be aromatic, each p orbital must overlap with p orbitals on adjacent atoms.
  • 11. 11 [2] A molecule must be planar. All adjacent p orbitals must be aligned so that the  electron density can be delocalized. Aeromatic compound (landscape)
  • 12. 12 [3] A molecule must be completely conjugated. Aromatic compounds must have a p orbital on every atom.
  • 13. 13 [4] A molecule must satisfy Hückel’s rule, and contain a particular number of  electrons. Benzene is aromatic and especially stable because it contains 6  electrons. Cyclobutadiene is antiaromatic and especially unstable because it contains 4  electrons. Hückel's rule:
  • 15. 1. Aromatic—A cyclic, planar, completely conjugated compound with 4n + 2  electrons. 2. Antiaromatic—A cyclic, planar, completely conjugated compound with 4n  electrons. 3. Not aromatic (nonaromatic)—A compound that lacks one (or more) of the following requirements for aromaticity: being cyclic, planar, and completely conjugated. https://www.youtube.com/watch?v=nrRH_xYSjE4&t=138s Considering aromaticity, a compound can be classified in one of three ways:
  • 17. Aromatic Heterocyclic Compounds A heterocyclic compound has hetero atom in the ring system other than carbon The heteroatom donates either one or two electrons to the  system Heteroatom donates two electronsHeteroatom donates one electron
  • 18.  A six-membered heterocycle with a nitrogen atom in its ring   electron structure resembles benzene (6 electrons)  The nitrogen lone pair electrons are not part of the aromatic system (perpendicular orbital)  Is it aromatic, anti-aromatic or non-aromatic?
  • 19.  A five-membered heterocycle with one nitrogen   electron system similar to that of cyclopentadienyl anion  Nitrogen atom is sp2-hybridized, and lone pair of electrons occupies a p orbital (6  electrons) 19 Is it aromatic, anti-aromatic or non-aromatic?
  • 20. Furan structure Furan and Thiphene structure are similar  Are these aromatic, anti-aromatic or non-aromatic?
  • 23. 23 • Hydrocarbons containing a single ring with alternating double and single bonds are called annulenes. • Completely conjugated rings larger than benzene are also aromatic if they are planar and have 4n + 2  electrons. • To name an annulene, indicate the number of atoms in the ring in brackets and add the word annulene.
  • 24. 24 • [10]-Annulene has 10  electrons, which satisfies Hückel's rule, but a planar molecule would place the two H atoms inside the ring too close to each other. Thus, the ring puckers to relieve this strain. • Since [10]-annulene is not planar, the 10  electrons can’t delocalize over the entire ring and it is not aromatic.
  • 30.  Simple aromatic hydrocarbons come from two main sources: coal and petroleum.  Coal is an enormously complex mixture made up primarily of large arrays of benzene-like rings joined together.  Thermal breakdown of coal occurs when it is heated to 1000 °C in the absence of air, and a mixture of volatile products called coal tar boils off.  Fractional distillation at coal tar yields benzene, toluene, xylene (dimethylbenzene), naphthalene, and a host of other aromatic compounds.
  • 31.  Benzene is a chemical that is a colourless or light yellow liquid at room temperature. It has a sweet odour and is highly flammable.  Natural sources of benzene include volcanoes and forest fires. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke.  https://www.youtube.com/watch?v=oA 75KZLzRxQ&t=116s
  • 33.  With reduction of benzene diazonium chloride with sodium stannite or hypophosphorus acid.  Benzene sulphonic acid on hydrolysis with superheated steam gives benzene.  C6H5.SO3H + H2O —> C6H6 + H2SO4  Sodium benzoate is heated with soda-lime (NaOH) and when it gets decarboxylated benzene is obtained.  https://www.youtube.com/watch?v=X10VZeQmFDo
  • 34.  Catalytic reforming  Toluene hydrodealkylation  Toluene disproportionation  Pyrolysis gasoline  Production from coal tar
  • 37. Aromatic Rings C=C 1600-1500 (stretching) =C-H 3100-3000 (stretching), 2000-1600 (phenyl ring substitution overtones) U S overtones Double bonds /hydrocarbons
  • 42. Principle types of reactions of BENZENE: • Electrophilic Substitution reaction https://www.youtube.com/watch?v=nhpXRjoWVHU • Nucleophilic Aromatic substitution https://www.youtube.com/watch?v=NsD8Q13ryHk
  • 44. USES • Important industrial solvent and precursor in the production of drugs, plastics, synthetic rubber, dyes, resins, nylon and synthetic fibers. *Aromatic hydrocarbons of commercial interest are benzene, toluene,ortho-xylene and para- xylene *e.g. The use of polystyrene foam, produced from benzene, contributes to make homes more comfortable, keeping them warm in winter and cool in summer. It also helps to reduce energy emissions and prevents leakage. * Synthetic rubbers, also derived from aromatics, gives tyres better road-hugging ability, especially on
  • 45. •In production of rubbers, lubricants, dyes, detergents, drugs, and pesticides. *e.g. Cumene and phenol, for example, both produced from benzene, are used as a starting material to make aspirin and penicillin, one of the first and still one of the antibiotic agents. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke. In a refrigertor for example interior panels are most often made out of tough, corrosion-resistant plastics such as ABS or high- impact polystyrene; clear, see-through drawers and compartments are made out of polystyrene or polycarbonate. More importantly, the foamed polyurethane, derived from toluene. Most of a CD consists of an injection-molded piece of clear polycarbonate: a plastic derived from benzene, through bisphenol A and cumene.
  • 46.  In clothes : acrylic fibres, polyester, nylon, luxurious fibres – linen, silk, cashmere wool – to give them more resistance all are aromatics.  Aromatics are used today in most of our sports equipment. From polyurethane footballs to nylon parachutes, from light running shoes to polyester swimwear, aromatics provide the materials.  Gas-burner, microwave oven, coffee machine, pots and pans, milk bottles and yoghurt pots, meat trays, eggs tray even the cutlery all rely on the input of the aromatics industry
  • 70. About 35 million tonnes aromatic compounds are produced worldwide every year. They are extracted from complex mixtures obtained by the refining of oil or by distillation of coal tar, and are used to produce a range of important chemicals and polymers, including styrene, phenol, aniline, polyester and nylon which are staring material of many organically synthesised products.