4.2

Question 1

Who isolated a colorless flammable liquid from whale oil in 1825?

Answer 1

Michael Faraday

Question 2

From which substance was benzene obtained for many years?

Answer 2

Coal tar

Question 3

Who suggested the structure of benzene as a six-membered ring in 1865?

Answer 3

Kekulé

Question 4

What type of bonds did Kekulé propose were present in the benzene structure?

Answer 4

Alternating single and double carbon-to-carbon bonds

Question 5

True or False: The Kekulé model explains all of benzene’s reactions.

Answer 5

False

Question 6

What reaction was expected of benzene when reacted with aqueous bromine?

Answer 6

Addition reactions

Question 7

What happens to bromine when it reacts with benzene?

Answer 7

It is decolourised

Question 8

What did Kekulé propose about the forms of benzene to explain its reactions?

Answer 8

Benzene had two forms that changed quickly

Question 9

Fill in the blank: The structure of benzene is a _________.

Answer 9

six-membered ring

Question 10

What bond length was determined for carbon-to-carbon bonds in benzene?

Answer 10

0.140 nm

This bond length is consistent across all carbon-to-carbon bonds in benzene.

Question 11

What are the bond lengths for carbon-to-carbon double and single bonds?

Answer 11

• Double bond: 0.135 nm
• Single bond: 0.147 nm

These values highlight the differences in bond lengths between single and double bonds.

Question 12

True or False: The Kekulé structure accurately represents the stability of benzene.

Answer 12

False

The resonance energy indicates that benzene is more stable than the Kekulé structure suggests.

Question 13

What is the term used to describe the difference in energy values that indicates benzene’s stability?

Answer 13

Resonance energy

Resonance energy reflects the extra stability of benzene compared to the expected energy from the Kekulé model.

Question 14

What is the bond angle between three adjacent carbon atoms in benzene?

Answer 14

120°

Question 15

What type of bonds do carbon atoms form in an ethene molecule (C2H4)?

Answer 15

Sigma (σ) bonds

Question 16

What is the molecular structure of benzene?

Answer 16

Planar molecule

Question 17

What is the remaining outer electron configuration for each carbon atom in benzene?

Answer 17

Overlapping p electrons above and below the plane of the molecule

Question 18

What type of orbital is created by the overlapping p electrons in benzene?

Answer 18

Localized pi (π) orbital

Question 19

Fill in the blank: In an ethene molecule, each carbon atom is bonded to _____ hydrogen atoms.

Answer 19

Two

Question 20

True or False: Benzene has localized pi (π) orbitals.

Answer 20

False

Question 21

In which type of molecule do the carbon atoms have a planar arrangement?

Answer 21

Benzene

Question 22

What type of bonds do carbon atoms form in benzene?

Answer 22

Sigma bonds with two other carbon atoms and one hydrogen atom

Each carbon atom in benzene is bonded to two other carbon atoms and one hydrogen atom.

Question 23

Where is the fourth outer shell electron of a carbon atom in benzene located?

Answer 23

In a 2p orbital, above and below the plane of the carbon atoms

This orbital arrangement contributes to the delocalized electron structure.

Question 24

What does the delocalized electron structure in benzene represent?

Answer 24

Electrons that are shared above and below the plane of carbon atoms

This delocalization is often depicted by a circle inside the hexagonal ring.

Question 25

What is the simplest type of aromatic system?

Answer 25

Compounds containing a single benzene ring ## Footnote These compounds represent the basic structure of aromatic chemistry.

Question 26

Name two examples of aromatic ring systems with fused sides.

Answer 26

* Naphthalene * Anthracene ## Footnote These compounds consist of multiple fused benzene rings.

Question 27

What types of atoms can be found in rings besides carbon?

Answer 27

Pyridine, CH₅N ## Footnote Pyridine is an example of a heterocyclic compound containing nitrogen.

Question 28

What is the reaction type that benzene typically undergoes?

Answer 28

Substitution reactions ## Footnote This allows the delocalised system of electrons to be retained.

Question 29

What happens to benzene if it undergoes an addition reaction?

Answer 29

The stable delocalised electron system is disrupted, resulting in a less stable product.

Question 30

What conditions are needed for the hydrogenation of benzene?

Answer 30

High temperatures and a nickel or platinum catalyst.

Question 31

What is required for the radical reaction of benzene with chlorine to occur?

Answer 31

Bright sunlight.

Question 32

Why is the use of Lindane restricted?

Answer 32

It is a toxic material that is very persistent in the environment.

Question 33

What is the general behavior of benzene in chemical reactions?

Answer 33

Benzene generally reacts by substitution reactions.

Question 34

What is the significance of the delocalised system of electrons in benzene?

Answer 34

It contributes to the stability of benzene.

Question 35

What is the characteristic reaction of arenes?

Answer 35

Electrophilic substitution.

Question 36

What does benzene have that makes it susceptible to electrophilic attack?

Answer 36

A delocalised ring of electrons.

Question 37

What is replaced by the incoming electrophile in electrophilic substitution?

Answer 37

A hydrogen atom (as H+).

Question 38

What is formed during the electrophilic substitution mechanism after the stability of the ring is disturbed?

Answer 38

An unstable intermediate (called a Wheland intermediate).

Question 39

Fill in the blank: The mechanism of electrophilic substitution involves replacing a hydrogen atom with an _______.

Answer 39

[incoming electrophile].

Question 40

What is nitration?

Answer 40

A nitration reaction involves replacing a hydrogen atom with a nitro group, NO2.

Question 41

What is the electrophile in a nitration reaction?

Answer 41

The electrophile is the nitryl cation (or nitronium ion), NO2+.

Question 42

What acids are used to produce the nitryl cation in nitration?

Answer 42

Concentrated nitric acid and concentrated sulfuric(VI) acid.

Question 43

What is the mechanism for nitration?

Answer 43

The nitryl cation reacts with benzene to form nitrobenzene.

Question 44

What is the temperature condition for nitration to avoid the formation of by-products?

Answer 44

The temperature must not exceed 50°C.

Question 45

What is nitrobenzene's state and color?

Answer 45

Nitrobenzene is a yellow liquid.

Question 46

How can nitrobenzene be reduced to phenylamine?

Answer 46

By using tin metal and hydrochloric acid.

Question 47

Fill in the blank: The nitro group is represented as _______.

Answer 47

NO2.

Question 48

What is the role of iron filings in the reaction between benzene and bromine?

Answer 48

Iron filings react with bromine to give iron (III) bromide ## Footnote Iron (III) bromide acts as a catalyst in the halogenation process.

Question 49

What conditions are necessary for benzene to react with bromine?

Answer 49

A catalyst such as iron filings, iron (III) bromide, or aluminium bromide is required ## Footnote The reaction does not occur at room temperature without a catalyst.

Question 50

What happens to the bromine molecule in the presence of iron (III) bromide?

Answer 50

The polarisation of the bromine molecule is more pronounced ## Footnote This increased polarisation allows for electrophilic substitution to occur.

Question 51

What type of reaction occurs when bromine is added to benzene?

Answer 51

Electrophilic substitution ## Footnote This involves the substitution of a hydrogen atom in benzene with a bromine atom.

Question 52

What is regenerated at the end of the reaction involving benzene and bromine?

Answer 52

Iron (III) bromide ## Footnote Iron (III) bromide acts catalytically during the reaction.

Question 53

What catalysts are commonly used in the chlorination of benzene?

Answer 53

Anhydrous aluminium chloride or iron (II) chloride ## Footnote These catalysts facilitate the chlorination reaction.

Question 54

How is the chlorination of benzene typically carried out in industry?

Answer 54

As a continuous process ## Footnote This method minimizes polychlorination.

Question 55

What insecticide can be manufactured from chlorobenzene?

Answer 55

DDT ## Footnote The reaction involves chlorobenzene and trichloroethanal.

Question 56

What is the Friedel-Crafts alkylation method used for?

Answer 56

Producing a new carbon-to-carbon bond, giving alkyl derivatives of benzene

Question 57

What are two examples of alkyl derivatives produced by Friedel-Crafts alkylation?

Answer 57

* Methylbenzene (C6H5CH3) * Ethylbenzene (C6H5C2H5)

Question 58

What is used in place of the halogen in the Friedel-Crafts alkylation reaction?

Answer 58

A halogenoalkane

Question 59

What catalyst is often used in Friedel-Crafts alkylation?

Answer 59

Anhydrous aluminium chloride

Question 60

What role does the ethyl carbocation play in the Friedel-Crafts alkylation reaction?

Answer 60

Acts as the electrophile for reaction with the benzene ring

Question 61

What problem arises from the introduction of an alkyl group onto the benzene ring?

Answer 61

It activates the ring towards further alkylation

Question 62

What technique is used to reduce the chance of polyalkylation in Friedel-Crafts alkylation?

Answer 62

Adding the halogenoalkane slowly to the benzene and the catalyst

Question 63

How does benzene typically react in chemical reactions?

Answer 63

By electrophilic substitution

Question 64

What type of compounds react similarly to chloroalkanes when treated with sodium hydroxide?

Answer 64

Aromatic compounds with a halogen atom on a side chain

Question 65

What is the bond length of aliphatic C - Cl?

Answer 65

0.177 nm

Question 66

What is the bond length of aromatic C - Cl?

Answer 66

0.169 nm

Question 67

What causes the stronger bond between carbon and chlorine in chlorobenzene?

Answer 67

A non-bonding p electron pair on chlorine overlapping with the ring-system of electrons

Question 68

What is required to produce phenol from chlorobenzene?

Answer 68

Forcing conditions

Question 69

Which chemical is reacted with chlorobenzene to produce phenol?

Answer 69

NaOH(aq)

Question 70

What are the conditions needed for the reaction to produce phenol from chlorobenzene?

Answer 70

300°C/increased pressure

Question 71

What byproduct is formed along with phenol in the reaction?

Answer 71

NaCl

Question 72

What is a useful co-product of the reaction when producing phenol from cumene?

Answer 72

Propanone