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What is the molecular formula of benzene?
Which of the following reactions does benzene NOT undergo?
Why was the straight chain structure for benzene ruled out?
What is the effect of resonance in the structure of benzene?
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Which statement about the molecular orbital structure of benzene is correct?
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What demonstrates that all hydrogen atoms in benzene are identical?
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Which of the following accurately describes the hybridization of carbon in benzene?
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What structural feature contributes to benzene's stability compared to other hydrocarbons?
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What is the bond length of C-C in benzene?
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Which of the following types of reactions does benzene primarily undergo?
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According to Huckel's Rule, how many π electrons must an aromatic compound have?
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Which catalyst is required for the halogenation of benzene?
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What is formed when benzene undergoes nitration?
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What type of carbocation intermediate is formed during the nitration of benzene?
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Which of the following is NOT one of the types of Electrophilic Aromatic Substitution reactions that benzene undergoes?
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Which of the following must be true for a compound to be considered aromatic according to Huckel's Rule?
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What effect do ring activating groups have on the reactivity of the benzene ring?
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Which of the following is categorized as a strongly deactivating group?
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Where do ring deactivating groups direct subsequent substituents?
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What is a primary use of DDT?
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What characteristic is associated with saccharin?
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Which statement about BHC is correct?
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Which type of group is characterized by decreasing electron density on the benzene ring?
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What is the soluble salt of saccharin commonly known as?
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What is the chemical formula of benzene?
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Which statement correctly describes Kekule's structure of benzene?
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What evidence contradicts Kekule's model regarding the bond lengths in benzene?
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What type of reaction does benzene undergo primarily?
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Which of the following statements is true about benzene's stability?
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What is a natural source of benzene?
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What significant feature of benzene does Kekule's structure fail to explain?
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What characteristic of benzene indicates it is a highly toxic substance?
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What is the result of the loss of a proton in the Friedel-Crafts Alkylation mechanism?
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Which group is considered a strongly activating group in electrophilic substitution reactions?
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What is the nature of the substituent X in the context of monosubstituted benzene?
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Which of the following describes the benzene ring after substitution occurs?
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What type of ion is formed during the electrophile formation step in Friedel-Crafts Acylation?
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Which of the following statements is true about the attack of an electrophile on benzene in electrophilic substitution reactions?
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What distinguishes ring activating groups from ring deactivating groups?
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Which factor primarily determines the reactivity of benzene towards electrophilic substitution?
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Study Notes
Benzene
Benzene is an organic, colorless chemical compound.
It is a highly flammable liquid with a sweet smell and high melting point.
The chemical formula of benzene is $C_6H_6$.
It has a boiling point of 80°C and is lighter than water.
Natural sources of benzene include volcanoes and forest fires.
It is also a natural part of crude oils.
Benzene is a highly toxic carcinogenic chemical.
Structure of Benzene
The molecular formula of benzene ($C_6H_6$) shows a high degree of unsaturation.
Sir August Kekule was the first scientist who introduced the chemical structure of benzene as a 6 membered ring structure.
He also proposed the presence of 3 alternate double bonds in benzene ring.
According to Sir Kekule the 3 alternate double bonds in benzene also changes their position rapidly to satisfy tetravalency of carbon.
Kekule Structure of benzene
Although Kekule structure of benzene satisfies the structural features of benzene and also explain the equivalent nature of hydrogen, but yet this structure fails to explain the unusual behavior of benzene.
Since this structure of benzene is a great discovery and significant approach by sir Kekule, hence , it is still in use.
Chemical Reaction
Benzene undergoes substitution reaction rather than addition reaction like other unsaturated compounds.
C-C Bond Length
According to Sir Kekule, two kinds of bond present in benzene, single & double bond.
C-C: Bond length (1.54 Å).
C=C: Bond Length (1.34 Å).
Experimentally it is seen that bond length between all carbon atoms is 1.39 Å.
Stability
Kekule's structure could not explain the stability of benzene towards oxidizing agents.
Evidences in the Structure of Benzene
From its elemental composition and molecular weight determination it is found that benzene contains 6-C & 6-H atoms.
Benzene has molecular formula C6H6 compared to Hexane C6H14, that confirms benzene as a highly unsaturated compound compare to hexane (C6H14).
Benzene reacts with bromine in the presence of AlCl3 (catalyst) to form Bromobenzene.
Only one (mono) bromobenzene is obtained that shows all 6 hydrogen atom in benzene were identical.
Resonance Structure of Benzene
To explain all the limitations of Kekule's Structure, it has been proposed that benzene is a resonance hybrid of two Kekule Structure.
Resonance Hybrid (A) is a very stable structure and this is why benzene undergoes substitution reaction very easily rather than addition reaction.
Molecular Orbital Structure of Benzene
Molecular orbital theory states that all carbon atoms of benzene are sp2 hybridized.
Each carbon atom forms two C-C sigma bonds and one C-H sigma bond.
Carbon atoms are still left with unhybridized P- orbitals that overlaps to form π bonds.
Chemical Structure of Benzene
All the sigma bonds in benzene lies in the same plane.
All bond angle = 120°.
All C-C bond length = 1.40 Å.
All C-H bond length = 1.09 Å.
Chemical Formula = C6H6.
Molecular Weight = 78 g/mol.
Aromatic Character (Huckle's Rule)
Benzene and compounds that resemble benzene in their chemical behavior are known as aromatic compounds.
They undergo substitution reaction rather than addition reaction.
Aromaticity is basically decided by Huckel's Rule.
Huckel's Rule
Compound should be Cyclic.
There should be a conjugation (delocalized electrons).
Compound should be planer.
Total number of π electrons should be (4n+2), where n = 0,1,2....
Chemical Reactions of Benzene
Most commonly benzene undergoes electrophilic substitution reaction (Electrophilic Aromatic Substitution Reaction).
In these reactions hydrogen atom of the aromatic ring is replaced by an electrophile.
Types of Electrophilic Aromatic Substitution Reaction
Halogenation.
Nitration.
Sulfonation.
Friedel Craft's Alkylation.
Friedel Craft's Acylation.
Halogenation of Benzene
Benzene reacts with Halogens (Br2, Cl2, I2) in the presence of Lewis acid catalyst (AICl3) to give Bromobenzene or Chlorobenzene or Jodobenzene.
Mechanism of Halogenation (Chlorination)
STEP-I: Formation of Electrophile (Chloronium Ion).
STEP-II: Attack of Electrophile on Benzene to form Carbonium Ion.
STEP-III: Loss of proton and formation of product (Chlorobenzene).
Nitration
Benzene reacts with concentrated HNO3 in the presence of concentrated H2SO4 to form Nitrobenzene.
Mechanism
STEP-I: Formation of Electrophile (Nitronium Ion).
STEP-II: Attack of Electrophile to form carbocation intermediate.
STEP-III: Loss of proton leads to the formation of Nitrobenzene.
Sulfonation
Benzene reacts with concentrated or fuming sulphuric acid to form Benzene Sulphonic Acid.
Mechanism
STEP-I: Formation of Electrophile (Sulpher Trioxide/SO3).
STEP-II: Attack of Electrophile on Benzene to form Carbocation.
STEP-III: Loss of proton leads to formation of Benzene Sulphonic Acid.
Friedel-Crafts Alkylation
Benzene reacts with Alkyl Group to form Alkyl Benzene.
Mechanism
STEP-I: Formation of Electrophile.
STEP-II: Attack of Electrophile to form Carbocation Intermediate.
STEP-III: Loss of proton leads to the formation of Methyl Benzene (Product).
Friedel- Crafts Acylation
Benzene reacts with Acyl Group to form Aromatic ketones (Acetophenone) in the presence of AlCl3.
Mechanism
STEP-I: Formation of Electrophile (Acylium Ion).
STEP-II: Attack of Electrophile to form Carbocation Intermediate.
STEP-III: Loss of proton leads to the formation of Acetophenone (Product).
Effect of Substituents
Benzene ring contains 6 Hydrogens and all 6 hydrogen of benzene are identical in nature.
When 1 Hydrogen of benzene is substituted by a group then it becomes monosubstituted Benzene.
This Monosubstituted benzene contains 3 positions: ortho, meta, para.
Types of Substituents/Groups
Ring Activating Groups.
Ring Deactivating Groups.
Ring Activating Groups
Increases the der reactivity of benzene towards Electrophilic Substitution Reaction.
Increases the e- density on benzene ring.
They are also known as Ortho- Para Directing Groups.
Ring Deactivating Groups
Decreases the reactivity of benzene towards Electrophilic Substitution Reaction.
Decreases the e- density on benzene ring.
They are also known as Meta directing Groups.
Benzene Derivatives
When Hydrogen atoms of benzene are replaced by new groups then, the new structures are known as Benzene Derivatives.
DDT.
Saccharin.
BHC.
Chloramine - T.
DDT (Dichloro Diphenyl Trichloro Ethane)
It is a highly toxic contact poison for wide variety of insects and works by disorganizing their nervous system.
It is applied as dusting powder or its aqueous solution is sprayed on the target site.
Saccharin
Saccharin is used as an artificial sweetening agent.
It provides products with increased stability, improved taste and lower production cost.
It is also added in various vitamin supplements and medicines.
Its soluble salt is known as Saccharin Sodium.
BHC (Benzene Hexachloride)
It is used as insecticides in crops farming.
It is also used in various pharmaceuticals.
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Description
This quiz covers essential information about benzene, including its properties, molecular structure, and historical context related to its discovery. Test your knowledge on the characteristics and chemical significance of this important organic compound.
