aromatic compounds and amines

Question 1

what electron system does benzene have

Answer 1

delocalised electron ring

Question 2

what is the formula for benzene

Answer 2

C6H6

Question 3

what are the problems with Kerkules structure

Answer 3

1. carbon carbon bonds are all the same length in the structure but we know double bonds are shorter
2. benzene does not undergo addition reactions easily even though the structure has double bonds present
3. we don’t get the expected isomers when we react benzene
4. the hydrogenation of benzene is 152kjmol-1 less than expected if the structure was correct

Question 4

why does benzene not undergo addition reaction easily

Answer 4

the delocalised electron ring is very stable and by removing these electrons to make another bond you make a less stable product

Question 5

what is the expected enthalpy of hydrogenation of cyclohexatriene and how do you know

Answer 5

-360 as it is 3x -120 and -120 is the enthalpy of hydrogenation of one double bond in cyclohexatriene

Question 6

why do we know benzene is more stable than cyclohexatriene

Answer 6

it requires more energy to hydrogenate benzene and therefore we know it requires more energy to break the delocalised system of electrons as less energy is given out when you break the bonds

Question 7

why is cyclohexatriene so stable

Answer 7

it has alternating double and single bonds causing delocalised electrons which can overlap in the p orbitals meaning the electrons can move between them and this partial delocalisation causes stability in a compound

Question 8

what type of reaction is nitration of benzene

Answer 8

nitration

Question 9

what are the reactants needed in nitration of benzene

Answer 9

concentrated H2SO4 and HNO3

Question 10

what is the mechanisms of nitration of benzene

Answer 10

electrophilic substitution

Question 11

what are the equation to make the electrophile needed in the nitration of benzene

Answer 11

1. HNO3 + H2SO4 –> H2N+O3 + HSO4-
2. H2N+O3 —–> H2O + +NO2

Question 12

what is the overall equation in forming the electrophile needed for nitration of benzene

Answer 12

HNO3 + H2SO4 —-> +NO3 + H2O + HSO-4

Question 13

what is an amine

Answer 13

a lone pair on a nitrogen with 3 single bonds

Question 14

what is the intermolecular bonding like between amines

Answer 14

hydrogen bonding between 1 and 2 amines

tertiary amines have dipole- dipole

Question 15

what is an aromatic amine

Answer 15

when you have a N joined to a benzene ring with a lone pair

Question 16

what is a cationic surfactant

Answer 16

quaternary ammonium salts with at least one long hydrocarbon tail which are partly soluble and insoluble in water

Question 17

what are uses of cationic surfactants

Answer 17

fabric softeners and hair products

Question 18

how do we measure the strength of a base

Answer 18

by how well it accepts protons

Question 19

what does a high electron density mean for a base

Answer 19

the higher the electron density of a lone pair the stronger the base will be

Question 20

what is a weaker base ammonia or ethylamine and why

Answer 20

Ammonia is a weaker base as there are no electron donating groups to cause the positive inductive effect whereas ethylamine has a positive inductive effect as the alkyl groups donate electron density to the N and its lone pair to become more available for protons

Question 21

what is a weaker base ammonia or phenylamine and why

Answer 21

phenylamine is a weaker base as it has a benzene ring that causes the nitrogen’s lone pair to become partially delocalised in the ring and is therefore less available to form a dative bond with a H+

Question 22

if the conditions for nucleophilic substitution of amines and halogenoalkanes is excess ammonia what is the main product

Answer 22

primary amines

Question 23

if the conditions for nucleophilic substitution of amines and halogenoalkanes is excess halogenoalkane what is the main product

Answer 23

quaternary salts

Question 24

can ammonia act as an electrophile to benzene and explain why

Answer 24

no as the delocalised ring in benzene repel the lone pair on the N

Question 25

what are uses of aromatic amines

Answer 25

explosives and dyes

Question 26

what are the two ways to make amines

Answer 26

1. React nitrobenzene with a reducing agent under reflux with tin and conc. HCL followed by NaOH
2. Reacting a nitrile with a reducing agent with LiAlH4 followed by dilute HCL