Aromatics And Amines

Question 1

What is an aliphatic chemical

Answer 1

One that contains straight or branched chain organic substances

Question 2

What is an aromatic / arene

Answer 2

One that contains benzene

Question 3

What is molecular formula of benzene

Answer 3

C6H6

Question 4

Describe the structure of benzene

Answer 4

Six carbon atoms in an hexagonal ring

Each carbon atom bonded to 2 carbons and one hydrogen atoms

Six p orbital electrons delocalised in a ring structure above and below the plane of carbon atoms

Question 5

Why is benzene a planar molecule

Answer 5

All the c-c bongs are the same and have a length and bond every between a c-c single bond and a carbon carbon double bond

Question 6

Why is benzene more stable than the theoretical structure by kekule

Answer 6

Enthaply of hydrogenation for benzene is 208 but for structure it’s 360 due to stability from delocalised electrons

Question 7

Why does benzene undergo electophilic substitution instead of addition

Answer 7

It would break the delocalised system which would disrupt the stability of of benzene, substitution preserved the stability also benzene has high electron density so it can attract electrophiles

Question 8

Why is benzene toxic

Why does methyl benzene react more readily

Answer 8

It is a carcinogen

The methyl side group releases electrons into the devalued system which makes it more attractive to electrophiles

Question 9

What is the mechanism for the nitration of benzene called

Answer 9

Electrophilic substitution

Question 10

What are the reagents for the nitration of benzene and conditions

Answer 10

Concentrated sulfuirc acid
Concentrated nitric acid

50 degrees Celsius

Question 11

What is the electrophiles in the nitration of benzene

Answer 11

NO2 +

Question 12

Why is nitration of benzenes and important reaction

Answer 12

Makes useful compounds like explosives and formation of amines which came be used in pharmaceuticals and dye

Question 13

What is the equation for the formation of the electrophiles in the nitration of benzene

Answer 13

HN03 + H2SO4 ->. NO2+ HSO4- H2O

Question 14

What is formed in the nitration of benzene

Answer 14

Nitrobenzene

Question 15

What is formed in friedel crafts acylation

Answer 15

A phenyl ketone

Question 16

What are the reagents and conditions for friedel crafts acylation

Answer 16

Acyl chloride in presence of anhydrous aluminium chloride catalyst

Question 17

What is the mechanism for friedel crafts acylation and what is the condition

Answer 17

Electrophilic substitution

Heat under reflux at 50 degrees c

Question 18

Why are friedel craft acylation reactions important

Answer 18

They introduce a reactive functional group onto benzene rings

Question 19

How are aromatic amines made by reducing nitrobenzene

Answer 19

Heat under reflux with concentrated hydrochloric acid and tin to form a salt ( c6h5nh3+cl-)

The salt reacts with the alkali naoh to form aromatic amine

Question 20

What type of reaction forms amines by nitrobenzene

Answer 20

Reduction

Question 21

Why do primary aliphatic amines act as bronsted Lowry bases

Answer 21

The lone pair of electrons in the nitrogen is readily available for forming a dative covalent bond with a H+ so it accepts a proton

Question 22

Why are primary aliphatic amines weak bases

Answer 22

Only a low concentration of hydroxide ions is produced

Question 23

Why are primary aliphatic amines stronger bases then ammonia

Answer 23

The alkyl groups are electron releasing and push electrons towards the nitrogen atom so the lone pair of electrons on nitrogen are more readily available

Question 24

Why are secondary amines stronger bases than primary amines

Answer 24

They have more alkyl groups substituted into the nitrogen atom in place of H so more electron density is pushed into the N atom so lone pair more readily available

Question 25

How do amines react with acids

Answer 25

They all react to form ammonium salts

Question 26

Why do primary aromatic amines not form basic solutions

Answer 26

The lone pair in he nitrogen delocalise with the ring of electrons in benzene so the nitrogen is less able to accept protons

Question 27

How can primary amines be formed by a halogenoalakne

What is formed with it

Answer 27

Reacting it with excess ammonia under reflux

Alkyl ammonium salt

Question 28

Why is using halogenoalakens to from primary amines not the best method

Answer 28

It doesn’t form a pure product because the the amine formed still has a lone pair on the nitrogen so it can keep reacting with the halogenoaljene to form secondary, tertiary and quaternary amines

Question 29

In the mechanism to form amines with halogenoalaknes why is excess ammonia used

Answer 29

2 ammonia molecules needed
Acts as nucleophile
Then acts as a base

Question 30

What are quaternary salts used as

Answer 30

Cationic surfactants (cleaning products)

Question 31

How do cationic surfactants work

Answer 31

The positive nitrogen is attracted to negatively charged surfaces like glass, hair, fibres and plastics

Non polar tail attracted to oil and grease, polar head attracted to water so mix to remove grease

Positive ammonium ion attracted to negatively charged fibres and hair so removes static so used in hair conditioner and fabric softeners

Question 32

How are amines prepared from nitriles (catalytic hydrogenation)

Answer 32

Convert halogenoalkane to nitrile using KCN in aqueous ethanol under reflux

Reduce nitrile to amine using LiAlH4 in other
Or reducing hydrogen using a nickel catalyst

Question 33

Advantage and disadvantage of producing amines by catalytic hydrogenation

Answer 33

Only produces primary amines

Used kcn which is toxic and it’s 2 steps so might have lower yield