Chapter 25

Question 1

What is benzene?

Answer 1

Benzene is an aromatic compound with six carbons atoms joined in a ring and formula C6H6

Question 2

What is the kekule model of benzene? Draw it

Answer 2

In 1865 German chemistry Kekulé suggested benzene is made up of a planar ring of carbon atoms with alternating single and double bonds

Diagram

Question 3

What facts disprove the kekulé model?

Answer 3

1) if benzene contained the c=c it should undergo electrophilic addition (eg decolourises bromine water) but it doesn’t
2) if Kekulé was correct you’d expect 3c-c bonds of length 154 pm and 3 c=c bonds of length 134 pm but in reality all bonds are 139 pm
3) if Kekulé was correct you’d expect benzene with three double bonds to have three times the enthalpy change of hydrogenation of cyclohexene with one double bond. You’d expect it to be three times -120 yet it is only -208

Question 4

Draw and explain the delocalized model of benzene

Answer 4

Each carbon in benzene uses 3 of its 4 electrons to make 3 sigma bonds
each carbon has one electron in a p orbital at a right angle to the plane
Adjacent p orbital electrons overlap sideways creating pi bonds
this system of pi barns creates a ring of electron density above and below the plane which are delocalised

Question 5

Which aromatic compounds are named as substituted benzene rings and give an example

Answer 5

Alkyl groups halogens and nitro groups for example ethyl benzene chlorobenzene or nitrobenzene

Question 6

Which aromatix compounds are named as a compound with a phenyl group attached and give an example

Answer 6

Alkyl chains with a functional group or compounds with 7 or more carbons are named as compounds with the phenyl group attached such as phenyl ethanone or phenyl octane

Question 7

How do you name an aromatic compounds with more than one functional group

Answer 7

If all the functional groups are the same pick any and count round the way which give you the smallest numbers if there are different functional groups start with The group which gives its suffix

Question 8

Name the conditions required for the nitration of benzene

Answer 8

50°C and a sulphuric acid catalyst

Question 9

Draw all three parts of the mechanism for nitration of benzene

Answer 9

Mechanism In notes

Question 10

Name the conditions required for the halogenation of benzene

Answer 10

A halogen carrier FECL3 and room temperature

Question 11

Draw all three parts of the mechanism for the halogenation of benzene

Answer 11

Mechanism in book

Question 12

Name the conditions for the alkylation and acylation of benzene

Answer 12

Reflux and aluminium chlorideAlCl3

Question 13

Draw the equation for the alkylation of benzene to ethyl benzene

Answer 13

in book

Question 14

Draw the reaction of the acylation of benzene to phenyl ethanone

Answer 14

in book

Question 15

What is an acyl group

Answer 15

A carbon double bond it to an oxygen

Question 16

Draw the functional group for an aldehyde

Answer 16

CHO

Question 17

Draw the functional group for ketone

Answer 17

COC

Question 18

Draw the functional group for in amine

Answer 18

NH2

Question 19

Draw the functional group for a carboxylic acid

Answer 19

COOH

Question 20

Draw the functional great for an Ester

Answer 20

COOC

Question 21

Compare the reactivity of alkenes with benzene In terms of localised and delocalised electrons

Answer 21

Alkanes decolourise bromine water in electrophilic addition reaction because the pi bond contains localised electrons which induce a dipole in the nonpolar bromine enabling it to act as an electrophile.
Benzene does not react very mean unless the halogen carrier catalyst is present because benzene has a delocalised pie ring of electrons which are less dense and localised there is insufficient density to induce a dipole

Question 22

What is Phenol

Answer 22

Phenol is an organic chemical containing a hydroxyl functional group directly bonded to an aromatic ring

Question 23

What type of acid is phenol and why

Answer 23

Phenol is a weak acid because it partially dissociates in water

Question 24

How can you tell phenol is more acidic than alcohols but less than carboxylic acid

Answer 24

Ethanol does not react with sodium hydroxide a strong base or sodium carbonate a weak base
Phenols and carboxylic acids react with sodium hydroxide a strong base
Only carboxylic acids are strong enough to react with sodium carbonate a weak base

Question 25

State the conditions and draw the reaction for the bromination of phenol

Answer 25

Conditions room temperature and textbook

Question 26

State the conditions and draw the mechanism for the nitration of Phenol

Answer 26

Conditions room temperature mechanism in textbook two products

Question 27

Compare the reactivity of Phenol and benzene

Answer 27

Bromine and nitric acid react more readily with phenol than benzene because the lone pair from the OH oxygen p orbital is donated to the pie system increasing electron density attracting Electrofiles

Question 28

What is a directing group

Answer 28

A functional group which directs substituents to certain positions

Question 29

What is an electron donating group

Answer 29

An electron donating group have electrons in orbitals overlap with the delocalised ring and increase its electron density at carbon is 24 and six so electricals are most likely to react here and direct substituents to these positions

Question 30

Give two examples of electron donating groups

Answer 30

0H and NH2

Question 31

What is an electron withdrawing group

Answer 31

An electron withdrawing group don’t have any orbitals which overlap with the delocalised ring and or electronegative so withdraws electron density from the ring at carbon 2 4 and six so directing them to carbon three and five

Question 32

Example of an electron withdrawing group

Answer 32

NO2

Question 33

Name and draw four exceptions to the naming of aromatic compounds

Answer 33

Benzoic acid, phenylamine, benzaldehyde and phenol