Aromatic Chemistry

Question 1

What is benzenes formula and structure

Answer 1

C6H6

Ring

Question 2

What is another name for arenes

Answer 2

Aromatic compounds

Question 3

What is the most common type of reaction of benzene

Answer 3

Substitution

Question 4

What is the shape of benzene

Answer 4

Flat, regular hexagon

Bond angle = 120

Question 5

What is the bond length between adjacent C atoms

Answer 5

Intermediate between C-C and C=C

Question 6

What happens to the 4th electron in the p orbital of each C atom in benzene

Answer 6

It delocalises to form rings of electron density above and below the hexagon, forming rings of delocalised electron density above/below the hexagon

Question 7

What is the effect on benzenes stability of the rings of electron density

Answer 7

Makes benzene very stable, even though it is unsaturated

Question 8

What is the thermochemical evidence that benzene is more stable than cyclohexane-1,3,5-triene

Answer 8

Benzene needs more energy to hydrogenate it

Question 9

Why is cyclohexane-1,3,5-triene not a suitable model for benzene

Answer 9

Not symmetrical like benzene
Would easily undergo addition reactions but benzene does not
Would form two isomers on the addition of Br2 but benzene does not

Question 10

What is the appearance of benzene at 298K

Answer 10

Colourless liquid

Question 11

Why does benzene have a relatively high melting point

Answer 11

Close packing of flat hexagonal molecules when solid

Question 12

Is benzene soluble

Answer 12

No as it is non polar

Question 13

Dangers of benzene

Answer 13

It is a carcinogen

Question 14

Why is benzene attacked by electrophiles

Answer 14

High electron density above/below ring to delocalised electrons

Question 15

What is delocalisation energy and why is the effect of this on benzenes reactions

Answer 15

The large amount of energy that is needed to break the aromatic ring apart
Results in the aromatic ring almost always staying intact

Question 16

What is seen when benzene is combusted

Answer 16

Smokey flame due to soot from unburnt carbon

This is because of the high carbon:hydrogen ratio

Question 17

What ion is used to nitrate benzene

Answer 17

NO2+

Question 18

How is this NO2+ ion generated

Answer 18

H2SO4 + HNO3 -> H2NO3+ + HSO4-
H2NO3+ -> H2O + NO2+

Overall:
H2SO4 + HNO3 -> HSO4- + NO2+ + H2O

Question 19

How is the H2SO4 catalyst regenerated in the nutrition of benzene

Answer 19

HSO4- + H+ -> H2SO4

H+ from benzene ring

Question 20

What are the uses of nitrated arenes

Answer 20

Production of explosives eg TNT

Question 21

How do substituents with a positive inductive effect further substitution

Answer 21

They release electrons into the delocalised electron ring, increasing the electron density and making further substitution reactions more quick

Question 22

How do substituents with a negative inductive effect further substitution

Answer 22

Remove electrons from the delocalised electron ring, decreasing the electron density and making further substitution reactions less quick

Question 23

What type of catalyst is used for Friedel-Crafts reaction

Answer 23

A halogen carrier

AlCl3

Question 24

What is happening when AlCl4- is formed in terms of electrons

Answer 24

Chlorine atoms line pair of electrons is forming a coordinate bond to Al

Question 25

How is the AlCl3 catalyst reformed

Answer 25

AlCl4- + H+ -> HCl + AlCl3

Question 26

In a cyclic compound, what might happen if two double bonds are next to each other

Answer 26

C=C bonds are in close proximity, so electrons in our cloud/p orbitals can partially delocalised and move between the two C=C double bonds

Question 27

What effect would electrons in p orbitals moving between the two C=C double bonds have on the stability of the molecule and it’s enthalpy of hydrogenation

Answer 27

Makes the molecule more stave | Makes enthalpy of hydrogenation more positive