Unit 11

Question 1

What is kekule’s structure

Answer 1

A Disproved Theory of the structure of Benzene

Question 2

What is the Bond structure and bond angles for benzene

Answer 2

Trigonal planar
120

Question 3

What is the evidence disproving kekules structure in relation to bromine water

Answer 3

If bromine was an alkene then it would be able to decolourise bromine water. However it does not. Therefore bromine is NOT an alkene

Question 4

What is the evidence disproving kekule’s structure in relation to enthalpy changes

Answer 4

The enthalpy change for the hydration of Cyclohexene is. -119 for one DB. Benzene has 3 DB and therefore should have a enthalpy change of -357 but in reality its -208. this shows that benzene more stable than presented in Kekule’s structure

Question 5

What is the evidence disproving kekule’s structure in relation to Bonding and structure

Answer 5

Traditionally single bond are longer than double bounds. At 0.134 in comparison to 0.154( in DB). This means that under kekule’s structure benzene would have an uneven shape. However the length of all the bond in Benzene are the same Giving it a regular structure .
All bonds are 0.140nm Sorter than a single bond but longer than a double bond.

Question 6

What is the name of the therory that cause bezene double bonds to be in dynamic equillibrium

Answer 6

resonance theory

Question 7

what is the cause of the blurry effect of benzene

Answer 7

Resonance which causes the double bonds to rapidly switch positions in the benzene ring

Question 8

Why is The benzene skeletal formula drawn with a circle in the middle.

Answer 8

It Represents the Delocalised system of electrons

Question 9

How can a pi cloud form

Answer 9

Two P orbitals overlapping vertically

Question 10

How can a sigma bond form

Answer 10

Two P orbitals overlapping horizontally
Two S orbitals overlapping
A P and S orbital overlapping

Question 11

How is the delocalised system of electrons formed in a benzene molecule

Answer 11

The overlapping of P orbitals above and below the carbon ring

Question 12

Why is benzene vulnerable to electrophilic attack

Answer 12

The electron rich area Created by the double bonds in the structure of benzene

Question 13

Why does benzene undergo electrophillic substitution rather than addition

Answer 13

Electrophilic addition will disrupt the stability of the delocalised system of electrons in benzene.
In order to maintain the stability of the system, Thee hydrogen removed must be replaced

Question 14

Define Aromatic

Answer 14

rings with delocalised system of electrons

Question 14

Define Aliphatic

Answer 14

Just chains molecules/ no Aromatic rings

Question 15

Define Alkyl

Answer 15

Branched chains of alkanes, e.g Methyl, Ethyl and Propyl groups.

Question 16

Define Aryl

Answer 16

Any structure with some kind of ring e.g Phenyl

Question 17

What are the two reactions of benzene

Answer 17

Combustion and neutralisation

Question 18

What is significant about the combustion of benzene

Answer 18

Create incredibly smokey flames
due to the low Hydrogen to carbon ration which caused lots of incomplete combustion===carbon particulates

Question 19

What are the three main steps behind the Electrophillic substitution of benzene

Answer 19

Formation of electrophile using a catalyst
Attack of electrophile
Reformation of the catalyst