Y2 Aromatic

Question 1

sigma bond

Answer 1

Consists of 2 overlapping s orbitals (covalent bond) - strong attraction between positive nucleus and electron cloud makes sigma bondsverystrong

Question 2

Pi bond

Answer 2

Consists of 2 overlapping p orbitals (2nd covalent bond in a C=C bond) - Has no electrons in the middle but electron cloud is in the top and bottom section - this makes pi bonds weaker thansigmabonds.

Question 3

What is enthalpy of hydrogenation

Answer 3

It is the enthalpy change when 1 mole of unsaturated compound is saturated by reacting it with hydrogen under standard conditions.

Question 4

kekule suggestion of benzene stucture vs actual one

Answer 4

Question 5

What is the enthalpy of hydration of cyclohexene, Kekule’s benzene, cyclohexane and actual benzene & which is most stable

Answer 5

Actual benzene is more stable that kekule’s benzene as more energy is needed to break the delocalised Pi bond system

Question 6

What is an arene

Answer 6

name hiven to a hydrocarbon based on a benzene compound

Question 7

Melting point of arenes

Answer 7

High relative to hydrocarbons with similar mr because benzene is fairly flat and molecules stacks on top of each other so greater surface area of contact and greater van der walls.

Question 8

observation during combustion of arenes

Answer 8

burns with a smokey flame

Question 9

Naming arenes

Answer 9

Question 10

Types of reactions that arenes undergo

Answer 10

• electrophilic substitution reactions
  -difficult to react
  -high electron density

Question 11

Evidence against Kekule’s benzene - Reactions with bromine water

Answer 11

cyclohexene has a C=C bond & hence decolourises bromine water. Benzene doesn’t decolourise bromine water implying that it doesn’t possess a C=C bond.

Question 12

Evidence against Kekule’s benzene - Bond lengths

Answer 12

Question 13

Evidence against Kekule’s benzene - lsomers of 1,2-dichlorobenzene

Answer 13

if kekules structure was correct then there would be 2 isomers of 1,2-dichlorobenzene but there is only 1 isomer of this compound so kekule is wrong.

Question 14

What is the actual Structure of Benzene

Answer 14

In benzene each carbon atom forms 3 bonds (sigma) with 2 neighbouring carbons and a hydrogen. The unbonded p orbitals on each carbon atom then
overlap with the p orbitals on neighbouring carbon
atoms to form a delocalised network of pi electrons
above and below the plane of carbon atoms.
This delocalised pi bond contains 6 electrons - 1
from each carbon atom. The delocalisation of
electrons makes the benzene ring 152 kJ more stable.

Question 15

What is an electrophile

Answer 15

electron pair acceptor e.g. NO2+,
CH3C+=O

Question 16

what are electrophilic substitution reactions & what is the general mechanism for this

Answer 16

A hydrogen atom from benzene is replaced with a nucleophile

Question 17

conditions for nitration of benzene

Answer 17

Conc. H2SO4 (catalyst)
Conc. HNO3 (used to form electrophile)
temp 50-60 degrees C

Question 18

Mechanism for nitration of benzene & equation for formation of electrophile

Answer 18

Question 19

TNT use and structure

Answer 19

TNT is 2,4,6-trinitromethylbenzene & is used for explosives

Question 20

Use of aromatic amines

Answer 20

making dyes

Question 21

Making aromatic amines - reaction & what combo of reactants are used as reductants in this reaction

Answer 21

Question 22

what is Friedel crafts Acylation and its mechanism

Answer 22

Question 23

what does phenol dissolve to form

Answer 23

It dissolves to form weak acids