Functional Group Chemistry

Question 1

What is amide to amide interconversion?

Answer 1

Annilines react with acid chloride in the presence of a base to form amides
The amide can also be hydrolysed back to the aniline by hearing with aqueous NaOH

Question 2

Why is amide to amide interconversion useful?

Answer 2

This can be used to control subsequent aromatic substitutions
This is because aniline is more reactive than the aromatic amide

Question 3

What happens when aniline is bromoniated?

Answer 3

NH2 is the strongest +M group and so reacts three times very quickly with no control of ortho versus para

Question 4

What happens when and amide aromatic reacts with bromine?

Answer 4

It only reacts once as the lone pair is delocalised into C=O and so it is less activating
Steric hindrance favours the para position

Question 5

What is nitro group reduction?

Answer 5

Aromatic nitro groups can be reduced to primary amines

Sn/HCl is used to reduce

Question 6

Why is nitro group reduction useful?

Answer 6

It is useful as it changes the positions to which the substituents directs electrophilic substitutions as NO2 is deactivating and NH2 is activating

Question 7

Aromatic primary amides can he converted into diazonium salts, why is this useful

Answer 7

Diazonium salts can be converted into many other functional groups

Question 8

How can you form a diazonium ion from benzene

Answer 8

1) HNO3/H2SO4= NO2
2) Sn/HCl= NH2
3) NaNO2/ HCl form HNO2 which generate NO+ (below 5c)
= N2+Cl
The diazonium salt is only stable below 5 degrees

Question 9

What reactions can diazonium ions undergo?

Answer 9

CuBr= Br
CuCl= Cl
CuCN= CN
KI= I
H2O/ heat= OH

Question 10

Why can you not form aliphatic diazonium salts?

Answer 10

They are too unstable to form even at low temperatures

Question 11

What are the reactions of diazonium salts called and by what do they proceed?

Answer 11

The reaction of diazonium salts with copper salts are called sandmeyer reactions and all proceed via an aryl radical

Question 12

How do the other diazonium salt reactions proceed?

Answer 12

Reactions with KI and water proceed via a phenyl cation and so are SN1 reactions

Question 13

What is the structure of a azo dye?

Answer 13

Ar-N=N-Ar

Question 14

How is aniline yellow synthesised?

Or other azo dyes ?

Answer 14

1) anniline reacts with diazonium salt
2) Cl- removes the proton

Step 1 is slow and step 2 is fast
This is a diazonium coupling reaction
For other azo dyes simply sub out the annlines

Question 15

What do diazonium coupling reaction require?

Answer 15

They require an activated +M aromatic ring to react with the diazonium salt
This is because the diazonium salt is stabilised by resonance

Question 16

How can you introduce a carboxylic acid into a benzene ring?

Answer 16

1) introduce an alkyl group by Friedel Crafts alkylation
2) oxidise it with potassium permanganate
This also changes the directing influence of the substituents from ortho para to meta as CO2H is deactivating

Question 17

What is potassium permanganate?

Answer 17

A very powerful oxidising agent which will cleave all C-C bonds and C-H bonds to CO2

Question 18

What is the rate of reaction of alkyls and aryls?

Answer 18

1) Alkyl-alkyl
2) alkyl- aryl
3) aryl- aryl

A very powerful oxidising agent which will cleave all C-C bonds and C-H bonds to CO2
But from the reactivity the reaction can be controlled to stop before the alkyl- alkyl, aryl- aryl CC bonds are broken

Question 19

How can you reduce ketones to alcohols?

Answer 19

Using the reducing agents NaBH4 or LiAlH4

Question 20

How can you reduce ketones to alkyl groups?

Answer 20

Zinc/ mercury amalgam and hydrochloric acid reduces ketones to alkyl groups

(Clemensen reduction)

Question 21

What happens to the directing influence in a clemensen reaction?

Answer 21

The directing influence changes from meta for the ketone to ortho/ para for the alkyl group

Question 22

What is the use of the clemensen reduction?

Answer 22

This provides an alternative to Friedel Crafy alkylation reactions which would require a primary carbenium ion (RCH2+) which is too unstable to form

Question 23

How do you convert sulfonic acid to H?

Answer 23

This reaction removes SO3H groups and is the reverse of putting in SO3H
The mechanism is the exact reverse for formation of sulfonic acid
You add dilute H2SO4(aq)/ heat
The reaction is reversible and controlled by Le Chateliers principle

Question 24

Can nucleophillic substitutions occur?

Can SN1 or SN2 reactions occur?

Answer 24

Yes under certain circumstances
SN1 reactions are possible on aromatic systems but require a very good leaving group (I.e a diazonium salt)
SN2 reactions are impossible
Nucleophiles cannot attack at 180 degrees to leaving group

Question 25

When is a positive charge in an aromatic system stabilised and destabilised?

Answer 25

A positive charge in an empty sp2 orbital, perpendicular to the pi system- this is not stabilised and so difficult to form
The positive charge is in an empty p orbital aligned with the pi system and so it is resonance stabilised

Question 26

How else can nucleophillic aromatic substitution occur?

Answer 26

It can also occur by addition elimination mechanism

Question 27

What requirements do addition elimination reactions have?

Answer 27

It needs a strong -I group which acts as the leaving group
The leaving group must be ortho or para to a strong -M group
This means the mechanism can only happen when electron withdrawing groups are attached
This makes it possible for the nucleophile to attack by conjugate or Michael addition

Question 28

Describe the mechanism of addition eliminating reactions

Answer 28

2 steps
1) slow conjugate addition of the nucleophillic ortho or para to the strongly electron withdrawing group (loses aromaticity)
2) fast elimination of the best leaving group to reform the ring
The -M group allows the nucleophile to attack the partially positive carbon as it acts as a sink for the electrons to go

Question 29

What is the needed regiochemistry for addition elimination reactions?

Answer 29

The leaving group and -M group must be ortho- or para to one another
If the leaving group and -M are meta to each other- no reaction occurs as there is not where for electrons to go in the first step as they cannot get to the -M group