6.1.1 aromatic compounds

Question 1

what is Kekules structure for Benzene

Answer 1

C6H6

Question 2

draw Kekules structure for Benzene and how many Sigma and Pi bonds it holds

Answer 2

12 sigma
3 pi

Question 3

describe the evidence used to refute Kekules model of benzene
(resistant to attack from electrophiles

Answer 3

Kekules model predicts that b Benzene should undergo electrophilic addition however Benzene does not undergo electrophilic addition and is resistant to attack from electrophiles EGHBR

Question 4

describe the evidence used to refute Kekules model of benzene
(enthaply of hydrogenation)

Answer 4

the enthalpy change of cyclohexene is -120 jkmol-1 so you would expect the theoretical value of benzene to be -120 x 3=-360 however it is actually lower at -208 this means Bezene is more stable than expected

Enthalpy change of hydration is less exothermic than expected

Question 5

what is the delocalisation energy of benzene

Answer 5

delocalisation energy of benzene-difference between the two values of enthalpy change of hydrogenation

Question 6

describe the evidence used to refute Kekules model of benzene
(c-c bond length)

Answer 6

its is between (1.40) the lenght of a single bond (1.55) and a double bond (1.34)
ALL C-C BONDS IN BENZENE ARE THE SAME LENGTH

Question 7

draw the delocalised pi bond model of benzene

Answer 7

in booklet
-1X delocalised pi bond
-6 electrons are shared over 6C atoms

Question 8

draw the kekule model of benzene

Answer 8

in booklet
-3X localised pi bond two
-2 electrons are shared between two carbon atoms

Question 9

describe the similarities between the Kekule model and benzene

Answer 9

both have a sideways overlap of P-orbitals above and below the plane of the molecule

Question 11

Hoe to get from Benzene to nitrobenzene

Answer 11

-refluxed on a water bath at 60 degrees celcius (want)
-Add conc HNO3 and conc H2SO4

Question 12

what is the reagent from benzene to nitrobenzene

Answer 12

conc HNO3

Question 13

what is the catalyst for benzene to nitrobenzene

Answer 13

conc H2SO4

Question 14

write out the overall equation from benzene to nitrobenzene

Answer 14

in booklet

Question 15

how do you get a polysubstitued benzene ring

Answer 15

if temperatures rise above 95
however you also have 2HNO3 and 2H2O

Question 16

how is the nitronium ions produced

Answer 16

2H2SO4 + HNO3 ———-> NO2+ + H3O+ + 2HSO4-

Question 17

draw the electrophillic attack on the benzene ring

Answer 17

in booklet

Question 18

what is the equation of the regeneration of the catalyst

Answer 18

H+ + HSO4- -> H2SO4

Question 19

write the overall equation for the halogenation of benzene

Answer 19

in booklet

Question 20

what is the catalyst for the halogenation of benzene if the halogen reaction is
eg-cl2, br2

Answer 20

Alcl2
Febr2
-these are the halogen carriers

Question 21

how is the electrophile formed equation

Answer 21

Cl2 + AlCl3 -> AlCl4- + CL+

br2 + FeBr3 -> Febr4- + Br+

Question 22

draw the equation for the electrophilic attack on the benzene ring

Answer 22

in booklet

Question 23

write the equation for the regeneration of the catalyst

Answer 23

H+ +Alcl4- -> Alcl3 + HCl

Question 24

when reacting benzene with a haloalkane would you need a halogen carrier

Answer 24

yes
eg- FeBr3, AlCl3

Question 25

complete the reaction of chloropropane with benzene

Answer 25

in booklet

Question 26

complete the mechanism for propanoyl chloride with benzene

Answer 26

in booklet

Question 27

draw a phenol group

Answer 27

benzene ring with an OH group

Question 28

what do phenols react with to form salts

Answer 28

as phenol is a weak acid it can react with a string base EG-NaOH to form salt

Question 29

what cant phenols react with

Answer 29

weak bases eg-NaCO3

Question 30

why do electrophilic substation reaction occur more readily with Phenol then benzene

Answer 30

the lone pair of electrons on the O atom is partially delocalised into the delocalised pi system this increase the electron density of the pi system in phenol so its more able to induce a dipole into the electrophille and is more suceptible to electrophillic attack

Question 31

what are the conditions you need when phenol react with bromine

Answer 31

room temperature and no catalyst

Question 32

what are the two observations you can produce when phenol reacts with bromine

Answer 32

-white precipitate of your produce -orange to colourless

Question 33

what is the equation for phenol reacting with bromine

Answer 33

in booklet -get 3Br and 3HBr

Question 34

what type of nitric acid does phenol react with

Answer 34

reacts with dilute nitric acid

Question 35

what are the conditions for phenol reacting with dilute nitric acid

Answer 35

room temperature no calalyst

Question 36

describe the OH and NH2 group

Answer 36

-it is an electron donating group (donates 2 electrons to pi system) -activates the 2,4 positions of benzene -so reacts more readily

Question 37

describe the NO2 group

Answer 37

-it is an electron withdrawing group (withdraws 2 electrons from the pi system) -activates the 3 position of benzene -so reacts less readily