Benzene and Aromatic Compounds

Flashcards on Benzene and Aromatic Compounds

Benzene

An important organic chemical compound with the chemical formula C6H6, composed of six carbon atoms in a ring with one hydrogen atom attached to each.

Arenes

Organic compounds containing one or more benzene rings.

Aryl Compounds

Compounds of benzene, also known as aromatic compounds.

Resonance in Benzene

The phenomenon where double bonds in benzene are not fixed but rotate across the ring.

Kekulé Structure

Equivalent representation of benzene with a hexagon and a circle inside.

Delocalized π electrons

π electrons that change position.

π electron distribution in Benzene

The six π electrons in the benzene ring are distributed over the six atoms of the ring.

Pi-bonds

There are three pi-bonds which makes the π elections to be Six in number

Actual bond length of Carbon to Carbon bond in benzene

1.39A

Criteria for Aromaticity

Cyclic, planar, completely conjugated, and contains (4n+2) π electrons.

Hückel's Rule

A rule stating that an organic compound is aromatic if it is cyclic, planar, completely conjugated, and contains (4n+2) number of π electrons where n=1,2,3…..

Aromatic Compound

Cyclic, planar, completely conjugated compound with (4n+2) π electrons.

Antiaromatic Compound

Cyclic, planar, completely conjugated compound with 4n π electrons.

Nonaromatic Compound

A compound lacking one or more requirements for aromaticity (cyclic, planar, conjugated).

Physical Properties of Benzene

Benzene is a colourless liquid, is highly flammable, has a sweet smell and it is the one responsible for the aroma around petrol stations.

Solubility of Benzene

Benzene is insoluble in water since water is Polar and soluble in non polar solvents such as alcohol, CHCl3, diethyl ether, acetone, acetic acid.

Chemical properties of Benzene

An unsaturated hydrocarbon that undergoes electrophilic aromatic substitution to retain its aromatic property.

Electrophilic Aromatic Substitution

A reaction where benzene retains its aromaticity.

Electrophile

An electron-loving species due to its electron deficiency.

Nucleophile

Electron rich specie

Halogenation

Replacement of H by X (X = Cl or Br)

Nitration

Replacement of H by NO₂

Sulfonation

Replacement of H by SO₂H

Friedel - Crafts alkylation

Replacement of H by R

Friedel -Crafts acylation

Replacement of H by RCO.

Halogenation Limitations

Reaction of benzene with I2 and F2 are not synthetically useful because I is too unreactive and F2 reacts too violently.

Nitration

The introduction of the -NO₂ group into a molecule.

Sulfonation of Benzene

Electrophilic substitution of Hydrogen for HSO₂. Benzene reacts with 503 in the preven encer of H₂504.

FRIEDEL-CRAFTS ACYLATION

RCO which is called an acyl group is added to the benzene, hence the process is called acylation.

HYDROGENATION OF BENZENE

When hydrogen is added to benzene, it forms Cyclohexane under special conditions

HALOGENATION OF BENZENE

When the halogen reacts.in the presence of ultraviolet light with benzene The reaction takes place by free-radical mechanism and the product is then fully saturated halogen

OZONOLYSIS OF BENZENE

Like the alkenes, benzene reacts with ozone to give an unstable ozonide this on hydrolysis gives ethanedial (glyoxal).

Preparation of Benzene (Decarboxylation)

Sodium benzoate + soda-lime (NaOH) with heat

Preparation of Benzene (Phenol Reduction)

Passing phenol vapors over heated zinc dust.

Preparation of Benzene (Ethyne Polymerization)

Passing ethyne through a red hot copper tube.

Preparation of Benzene (Diazonium Reduction)

Reduction of benzene diazonium chloride with sodium stannite or hypophosphorus acid.

Preparation of Benzene (Sulfonic Acid Hydrolysis)

Hydrolysis of benzene sulfonic acid with superheated steam.

Major Processes for Benzene Production

Catalytic reforming; Toluene hydrodealkylation; Toluene desproportionation; Pyrolysis gasoline; Production from coal tar

Major Use of Benzene

As an intermediate to make other chemicals like ethylbenzene, cumene, cyclohexane, nitrobenzene and alkylbenzene.