C25- Aromatic compounds

Question 1

What type of reaction does benzene do

Answer 1

electrophilic substitution

cannot do addition

Question 2

conditions for nitration of benzene

Answer 2

use CONCENTRATEDis phenol acidic sulfuric acid and nitric acid at 50c

Question 3

what happens if temp greater than 50c used to nitrate benzene

Answer 3

further substitution of NO2

Question 4

equation for how to generate NO2+ electrophile

Answer 4

HNO3 + H2SO4 –> H2NO3+ + HSO4-

H2NO3 –> H2O + NO2+

Question 5

3 stages of electrophillic substitution

Answer 5

generating the elcetrophile

electrophilic substitution

regeneration of catalyst

Question 6

name of catalyst used to halogenate benzene

general

Answer 6

halogen carrier

Question 7

Example halogen carriers

Answer 7

AlCl3

AlBr3

FeCl3

Question 8

Conditions need to halogenate benzene

Answer 8

RTP

halogen carrier catalyst and the halogen

Question 9

what doe sin situ mean in a chemical reaction

Answer 9

in the reaction vessel

Question 10

Why are acylation and alkylation reactions of benzene useful in organic synthesis

Answer 10

inc n of C in molecule

Question 11

Alkylation of benzene what and how

Answer 11

substitute a h on benzene for alkyl group

using AlCl3 catalyst

Haloalkane reagent

Question 12

what is acylation of benzene

Answer 12

reacting benzene with an acyl chloride

Question 13

Why do alkenes decolourise bromine water

in depth

Answer 13

Pi bond in alkene contains localised areas of e- density in the double bond, producing area of high e- density

localised e- in pi bond induce a dipole on br2, forming partial charges

Br delta+ can then act as an electrophile

Question 14

why can benzene not react with bromine water

Answer 14

E- are delocalised not localised like in alkenes

e- density spread across carbon ring

when non polar molecule approaches there’s insufficient areas of electron density to polarise it

Question 15

3 points to disprove kekulés model

Answer 15

Doesn’t decolourise bromien water, so no C=C bond as no electrophilic addition reaction

Length of carbkn bonds, between single and double found using x-ray difraction

Hydrogenation enthalpy is less than 3 times that of cyclohexene, so stucture is not 3 C=C bonds, actually structure of benzene is more stable

Question 16

Describe the formation of the deloaclised model

Answer 16

Each Carbon atom is bonded to two others and a hydrogen atom so has one electron in a p orbital

P orbitals overlap sideways to form a ring of electron density

Overlapping p orbitals create a pi bond system spread under and above the carbon ring

Electrons are delocalised

Question 17

Catalyst needed for acylation and alkylation of benzene

Answer 17

AlCl3

Question 18

How does cyclohexene react with Br2

Answer 18

Pi bond in alkene has localised electrons above and below C=C forming areas of high electron density

This induces a dipole on Br2 framing a partially positive Br that acts as an electrophile

Question 19

Why can benzene not react in an addition reaction with benzene

Answer 19

Benzene electrons are delocalised as pi electrons are spread above and below carbon plane

Electron density is lower

Non polar molecules are not polarised

Question 20

reagents to reduce nitrobenzene to phenylamine

Answer 20

sn / conc HCl

Question 21

Why does phenol react more readily than benzene

Answer 21

Lp on oxygen donated into the pi system increasing electron density

Electrophile is more polarised

Question 22

How does the bonding in the kekule model of benzene differ from the accepted model

Answer 22

Contains alternating double and single bonds.

Question 23

Rule for directing groups

Answer 23

If atom bonded directly to benzene has a lp then its a 2,4 directing group.

If atom next to one bonded to benzene has a lp then a 3 directing group

Question 24

Benzene to phenyl amine pathway

Answer 24

benzene to nitrobenzne then to phenyl amine

Question 25

COOH effect on benzene

Answer 25

withdrawing group reduces electron density in ring electrophiles are much less polarised