6.1 AROMATIC COMPOUNDS AND CARBONYLS

Question 1

Benzene

Answer 1

• has the formula C6H6

- has a cyclic structure, with its 6 carbon atoms joined together in a ring

Question 2

Arenes

Answer 2

• compounds containing a benzene ring

Question 3

Naming Arenes

Answer 3

• short alkyl side chains, halogens and nitro groups are prefixes to ‘benzene’ when naming arenes
• we use ‘phenyl’ as a prefix to alkyl side chains greater than 7 carbon atoms long, or alkyl side chains with a functional group

Question 4

Electrophilic Substitution of Benzene

Answer 4

• results in a hydrogen atom being substituted by an electrophile
• is a two step mechanism:
  1) the addition of the electrophile to form a positively charged intermediate
  2) the loss of a H+ from the carbon atom attached to the electrophile, which reforms the delocalised ring

Question 5

Halogen Carriers

Answer 5

• are catalysts that make some compounds into stronger, more polarised electrophiles, in order for them to be able to attack the stable benzene ring
• accepts a lone pair of electrons from a halogen atom on an electrophile and as the lone pair of electrons is pulled away, the polarisation in the molecule increases, making the electrophile stronger
• includes aluminium halides and iron halides

Question 6

Halogenation

Answer 6

• benzene will react with halogens in the presence of an aluminium halide catalyst
• the catalyst polarises the halogen, allowing one of the halogen atoms to act as an electrophile
• during the reaction, a halogen atom is substituted in place of a hydrogen atom

Question 7

Friedel-Crafts Reactions

Answer 7

• are useful for forming C-C bonds in organic synthesis

- are carried out by refluxing benzene with a halogen carrier and either a haloalkane or an acyl chloride

Question 8

Friedel-Crafts Alkylation

Answer 8

• puts an alkyl group onto a benzene ring using a haloalkane and a halogen carrier
• the general reaction is:

C6H6 + R-X –> C6H5R + HX

Question 9

Friedel-Crafts Acylation

Answer 9

• substitutes an acyl group for a H atom on benzene
• benzene has to be refluxed with an acyl chloride
• produces phenylketones or benzaldehyde if R=H
• the general reaction is:

C6H6 + RCOCl —> C6H5COR + HCl

Question 10

Making Nitrobenzene

Answer 10

• nitrobenzene is made when you warm benzene with concentrated nitric acid and concentrated sulfuric acid
• sulfuric acid is a catalyst, so it helps to make the nitronium ion, NO2 +, which is the electrophile, and is then regenerated at the end of the reaction mechanism
• the temperature needs to be kept at 50 degrees celcius