Year 13- Aromatic chemistry

Question 1

What does aromatic/arene mean?

Answer 1

has one or more rings of 6 carbon atoms with delocalized bonding

Question 2

Benzene’s basic structure

Answer 2

• six carbons in a hexagonal ring with a H bonded to each C atom
• each C bonded to 2 other C’s and one H in a single covalent sigma bond. this leaves one unused electron on each c atom in a p orbital, perpendicular to the plane of the ring

Question 3

How is benzene a planar molecule?

Answer 3

all C-C bonds are the same and have a length and bond energy between C-C and C=C bond

Question 4

How is cyclohexene more stable than cyclohexa-1.3.5–triene?

Answer 4

theoretically, there are 3 double bonds in 1.3.5-triene so we’d expect the amount of energy to be 3 times as much as cyclohexane.
however, it is less as the 6 pi electrons are delocalised, not in 3 double bonds.

Question 5

How do we name aromatic molecules with more than one diff substituent?

Answer 5

in alphabetical order and use di or tri.

Question 6

In other molecules, what is benzene regarded as? How would you name them?

Answer 6

as a substituent side group.

a C6H5 group is a phenyl group.

Question 7

Why doesn’t benzene generally undergo addition reactions?

Answer 7

it would involve breaking the delocalized system. this is why we use substitution reactions with one H being substituted.

Question 8

Why does benzene undergo electrophilic substitution?

Answer 8

it has a high electron density so attracts electrophiles

Question 9

Why is benzene banned in schools?

Answer 9

its a carcinogen, so we use methylbenzene as it is less toxic and reacts more readily as the methyl group releases electrons into the delocalised system making it more attractive to electrophiles.

Question 10

Nitration of benzene- reagents, electrophile

Answer 10

R: conc nitric acid in the presence of conc sulfuric acid (catalyst)
E: NO2 +

Question 11

Equation for the formation of NO2 +

Answer 11

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

The HNO3 acts as a base

Question 12

Why is the nitration of benzene done at 60*C?

Answer 12

because anything higher would make a 2nd nitro group be substituted

Question 13

Friedel Crafts acylation- product, reagents, conditions

Answer 13

P= phenyl ketone
R= acyl chloride in the presence of anhydrous aluminum chloride catalyst 
C= heat under reflux (50*C)

Question 14

Equation for the formation of electrophile- Friedel crafts

Answer 14

AlCl3 + CH3COCl –> CH3CO + + AlCl4 -

Question 15

Reduction of nitrobenzene to aromatic amines- reagents, conditions

Answer 15

R= Sn and HCl or Fe and HCl
C= heating

Question 16

What happens if an OH group, Cl atom and NH2 group are directly attached to the benzene ring?

Answer 16

the delocalisation will extend to include the lone pair on the N, O and Cl.

Question 17

What happens when a Cl atom is bonded to a benzene ring?

Answer 17

the C-Cl bond is stronger. halogenoalkane substitution and elimination reactions don’t occur. the electron chich benzene ring repels nucleophiles.

Question 18

What happens when an OH group is bonded to a benzene ring?

Answer 18

it is called phenol. delocalization makes the C-O bond stronger and the OH bond weaker. phenol doesn’t react like an alcohol as it is more acidic and doesn’t oxidise.

Question 19

What happens when an NH2 group is bonded to a benzene ring?

Answer 19

it is called phenylamine. less basic than aliphatic amines as lone pair is delocalized and less available to accept a proton.