Beznene 3

Question 1

What is the molecular formula of benzene?

Answer 1

C6H6

Question 2

Describe the bonding in benzene.

Answer 2

Each carbon forms three sigma (σ) bonds, and the remaining p-orbitals overlap to form a delocalized π-electron cloud above and below the ring.

Question 3

Why is benzene considered aromatic?

Answer 3

Benzene has a delocalized system of π-electrons and follows Hückel’s rule for aromaticity (4n + 2, where n = 1).

Question 4

What is unique about the bond lengths in benzene?

Answer 4

All C–C bond lengths in benzene are equal at about 140 pm, intermediate between single and double bonds.

Question 5

What happens in the first step of an electrophilic substitution reaction in benzene?

Answer 5

An electrophile is generated.

Question 6

What occurs when an electrophile reacts with benzene in electrophilic substitution?

Answer 6

The electrophile attacks the π-electron cloud of benzene, forming a carbocation (arenium ion) intermediate.

Question 7

How is the aromaticity of benzene restored in electrophilic substitution?

Answer 7

The intermediate is deprotonated by a base, restoring aromaticity.

Question 8

What are the reagents and product of the nitration of benzene?

Answer 8

Reagents: HNO3 and H2SO4; Product: Nitrobenzene.

Question 9

What electrophile is involved in the halogenation of benzene, and what catalyst is required?

Answer 9

Electrophile: X+ (e.g., Cl+, Br+); Catalyst: Lewis acid (e.g., FeCl3, FeBr3).

Question 10

What is the electrophile in Friedel-Crafts alkylation, and what product is formed?

Answer 10

Electrophile: Alkyl cation (R+); Product: Alkylbenzene (e.g., toluene).

Question 11

What reagents are required for Friedel-Crafts acylation?

Answer 11

Reagents: Acyl chloride (RCOCl) and AlCl3.

Question 12

What electrophile is involved in the sulfonation of benzene?

Answer 12

Electrophile: Sulfur trioxide (SO3).

Question 13

What types of groups are ortho/para-directing in electrophilic substitution?

Answer 13

Electron-donating groups, such as -OH, -CH3, and -NH2, are ortho/para-directing.

Question 14

What types of groups are meta-directing in electrophilic substitution?

Answer 14

Electron-withdrawing groups, such as -NO2, -CN, and -COOH, are meta-directing.

Question 15

What effect do activating groups have on electrophilic substitution reactions in benzene?

Answer 15

Activating groups increase the reactivity of the benzene ring towards electrophiles, usually directing to the ortho and para positions.

Question 16

What effect do deactivating groups have on electrophilic substitution reactions in benzene?

Answer 16

Deactivating groups decrease the reactivity of the benzene ring towards electrophiles, often directing substitution to the meta position.