aromatic chemistry

Question 1

Huckel’s rule

Answer 1

4n + 2 pi electrons

Question 2

Anti-aromatic conditions

Answer 2

4n pi electrons

Question 3

Pi system of pyridine description

Answer 3

six membered ring with a nitrogen atom in the ring. The nitrogen lone pair of electrons do not contribute towards the pi system and as a result is a weak base

Question 4

Pyrrole description

Answer 4

Five membered cyclic ring with one nitrogen. The sp2 hybridized nitrogen donates its lone pair of electrons in a p orbital to the pi system. Therefore not a base

Question 5

Mechanism of electrophilic aromatic substitution

Answer 5

See notes

Question 6

Which is the rate determining step of electrophilic aromatic substitution and why

Answer 6

The initial attack on the electrophile. Aromaticity is hard to lose, easy to gain so the second step in which aromaticity is regained is rapid by comparison

Question 7

Lewis acids used for electrophilic aromatic substitution

Answer 7

AlCl3, AlBr3, H2SO4

Question 8

Electrophiles used to electrophilic aromatic substitution

Answer 8

Cl2, Br2, HNO3, SO3, RX, RCOX

Question 9

Limitations of Friedel-Crafts alkylations

Answer 9

They are prone to carbocation rearrangements, deactivated benzene rings are not reactive to it, over alkylation is possible as the product is more reactive than the starting material, the Lewis acid catalyst AlCl3 complexes aryl amines making them unreactive.

Question 10

With what substituents does Friedel-Crafts acylation not occur

Answer 10

Benzene rings with amine substituents

Question 11

Benefits of acylation as supposed to alkylation

Answer 11

The final product is a deactivated benzene ring, inability of the acylium ion intermediate to rearrange

Question 12

Stability of the acylium ion

Answer 12

Resonance

Question 13

Product of acylation

Answer 13

Benzene with a ketone substituent

Question 14

Reduction of acylation products to theoretical alkylation product

Answer 14

Zn(Hg)/ HCl, heat

Question 15

Describe the reason for ortho, para and meta directing aromatic substitutents

Answer 15

See notes

Question 16

Product of the bromination of anilines

Answer 16

Tri-bromo substituted aniline

Question 17

Control over the bromination of anilines

Answer 17

Oxidation to an amide allows for steric hinderance of the ortho positions and so a single bromine is substituted at the para position

Question 18

Which are more reactive to electrophilic aromatic substitution, phenols or anilines

Answer 18

Anilines, phenols have some control over the level of substitution

Question 19

Halides activation and directing characteristics

Answer 19

Halides are deactivating as a result of their high electronegativity however, their accessible lone pairs make then ortho and para directing as supposed to meta

Question 20

Reduction of a nitro group to diazonium salts

Answer 20

H2, Pd/C to give the amine. NaNO2/HCl to give the diazonium salt

Question 21

Pros and cons of using deactivated benzene reagents

Answer 21

They react slower but react for form less of a mixture of products

Question 22

Nitro group to amine reagents

Answer 22

H2, Pd/C, EtOH
OR
Sn/HCl

Question 23

Ketone to alkyl reagents

Answer 23

Zn(Hg) / HCl, heat

Question 24

Alcohol to ether reagents

Answer 24

NaH, CH3I

Question 25

Amine to amide reagents

Answer 25

CH3COCL, pyridine

Question 26

Description of nucleophilic aromatic substitution

Answer 26

A nucleophile displaces a good leaving group on an aromatic ring. Needs a strong nucleophile e.g. oxide salt

Question 27

Nucleophilic aromatic substitution mechanism

Answer 27

See notes

Question 28

Why does the location of the electron withdrawing group on the aromatic ring undergoing nucleophilic substitution matter

Answer 28

The EWG must be para. The delocalisation of charge in the intermediate means that the attack by the nucleophile can only be ortho or para (para being where the LG is)

Question 29

Which is the RDS of nucleophilic aromatic substitution

Answer 29

Addition of the nucleophile (first step)

Question 30

Meisenheimer intermediate

Answer 30

Nucleophilic substitution intermediate. NO2 acts as the EWG. Stabilised through delocalisation and is not aromatic

Question 31

Benzylic substitution

Answer 31

The substitution of a LG on the carbon substituent of a benzene ring

Question 32

Benzylic substitution mechanism

Answer 32

See notes

Question 33

How many products are their following a benzylic substitution

Answer 33

One

Question 34

Stabilisation of the benzylic intermediate

Answer 34

Carbocation resonance with the benzene ring

Question 35

Removal of an alcohol or amine on a carbon adjacent to an aromatic ring

Answer 35

H2, Pd/C