aromatic compounds carbonyls and acids

Question 1

explain how kekule discovered his model

Answer 1

when one group was added only one isomer was formed, but when two groups where added, three structural isomers where fromed

Question 2

describe kekule’s model

Answer 2

benzene was a 6 carbon ring with alternating between single and double bonds

Question 3

state the reasons why kekule’s model is wrong

Answer 3

all 6 carbon bonds are the same length
unlike alkanes benzene is resistant to addition reactions
enthalpy of of hydrogenation of benzene shows that benzene is more stable than predicted

Question 4

what peace of evidence about benzene can explain the real structure of benzene

Answer 4

benzene has a ring of delocalised electrons

Question 5

explain benzene’s delocalised structure

Answer 5

electrons form the p-orbitals combine for form a ring of delocalised both above and below the molecule. the free moving electrons are what makes benzene’s bonds all the same length. the delocalised ring is also what makes benzene stable as a lot of energy is needed to overcome the delocalisation of benzene

Question 6

what form of reactions does benzene undergo

Answer 6

substitution reactions to form benzene derivatives

Question 7

name the types of benzene derivatives

Answer 7

chlrobenzene, bromobenzene, nitrobenzene and alkylbenzenes e.g methylbenzene

Question 8

how many substitution reactions can benzene undergo

Answer 8

single, double and multiple substitutions can occur

Question 9

explain how naming of benzene structures are formed

Answer 9

first the prefix are put in alphabetical order, then they are given a number. no mater where the functional groups are n the ring the smallest number is always used first

Question 10

what the the prefix of benzene

Answer 10

phenyl group

Question 11

describe the process of electrophilic substitution

Answer 11

electrons in the delocalised rings around benzene attract and electrophile
a covalent bond is formed between the electrophile and electrons from the delocalised rings, this breaks the rings
a reactive intermediate if formed
the unstable intermediate releases a hydrogen ion so the final product is formed and the delocalised ring is reformed

Question 12

in nitration of benzene why is concentrated sulfuric acid used as a catalyst

Answer 12

the sulfuric acid is needed to generate the nitro ion form the nitric acid. however the sulfuric acid is regenerated at the end of the reaction

Question 13

describe the process of nitration of benzene

Answer 13

concentrated nitric acid and sulfuric acid are mixed in a ice bath so nitro ions form, then the benzene is added and a reflux condenser is set up to keep the reaction at around 50 degrees, in order to prevent further substitution

Question 14

why is a halogen carrier used in halogenation of benzene

Answer 14

halogen carriers are used because benzene is too stable to react with with halogen on its own, so iron or aluminium is used as a carrier, which is regenerated at the end of the reaction

Question 15

how does halogenation of benzene occur

Answer 15

first a halogen carrier is generated in situ from a halogen and either iron or aluminium. the halogen carrier then reacts with benzene in a substitution reaction much like nitration, the halogen carrier is regenerated along with the release of a hydrogen ion to reform the benzene delocalised ring.