3.7 aromatic compounds

Question 1

what do aromatic compounds all contain?

Answer 1

a benzene ring

Question 2

what is the structure of benzene?

Answer 2

C6H6
planar,cyclic structure
each c forms single covalent bonds to the carbons on either side and to 1 hydrogen
unpaired electron oon each c is located in a p orbital that sticks above and below the plane of the ring.
p-orbitals on each c form a ring of delocalised electrons

Question 3

what is the length of the bonds in a benzene ring?

Answer 3

all the same length (140pm)
between the length of a single C-C and double C=C

Question 4

why is benzene more stable than cyclohexa-1,3,5-triene would be?

Answer 4

because of the delocalised electron ring system
in a delocalised ring, the electron density is shared over more atoms so energy of the molecule is lowered and it becomes more stable

Question 5

evidence for benzene being more stable than cyclohexa-1,3,5-triene

Answer 5

see book

Question 6

how to name aromatic compounds

Answer 6

practice
suffix benzene or prefix phenyl

Question 7

why does benzene attract electrophiles?

Answer 7

because it is a region of high electron density

Question 8

what mechanism does benzene go through?
why?

Answer 8

electrophilic substitution
because it is so stable so doesnt undergo electrophilic addition as this would destroy the electron ring

Question 9

describe the electrophilic substitution mechanism of benzene

Answer 9

electron dense region at centre of ring attracts a nucleophile
electrophile steals pair of e- from centre of ring and gives molecule a + charge
to regain stability of benzene ring, c which is now bound to electrophile loses a h

Question 10

what is nitration?

Answer 10

when you warm benzene and conc sulfuric acid, you get nitrobenzene.
overall eq is:
HNO3 + benzene -> nitrobenzene + H2O

Question 11

what is the sulfuric acid catalyst for in nitration?
equation for making NO2+

Answer 11

helps make nitronium ion (NO2+) which is the electrophile
formation of NO2+ is first step of reaction mechanism
eq is
HNO3 + H2SO4 -> HSO4- + NO2+ + H2O
(once formed it can react w benzene through electrophilic sub)

Question 12

what are the uses of nitration reactions?

Answer 12

nitro compounds can be reduced to form aromatic amines
these are used to manufacture dyes and pharmaceuticals
nitro compounds decompose violently when heated so they are heated so are used as explosive such as TNT