27 Aromatic Chemistry

Question 1

Bonding and structure of benzene

Answer 1

Does not easily addition reactions
All the carbon-carbon bonds are the same size

hexagon wouldn’t be symmetrical (double bonds are shorter than single bonds)

(The nature of the bonding in a benzene ring, limited to planar structure and bond length intermediate between single and double)

Question 2

Arenes

Answer 2

Arenes are hydrocarbons based on benzene

Very stable

Question 3

Beneze

Answer 3

unsaturated ring of six carbon atoms

Question 4

Kekule

Answer 4

idea= publish a paper in which he suggested that benzene’s structure was based on a ring of acorn altering double and single bonds

double-bond alternate (resonance theory)
1,3,5
2,4,6

problem = reacts with bromine = doesn’t show addition recations

Question 5

aromatic stability

Answer 5

overlapping p-orbitals

Delocalisation of p electrons makes benzene more stable than the theoretical molecule cyclohexa-1,3,5-triene

Question 6

reactivity of benzene

Answer 6

electrophilic substitution

leaves the aromatic system unchanged (addition would need extra energy to destroy the aromatic system)

Question 7

properties of Benzene

Answer 7

colourless liquid at room temp
boils at 535k
freeze at 279k
benzene flat molecule (packed together very well in solid state so are harder to separate)
non polar
don't mix with water

Question 8

arenes burnt in air

Answer 8

unburnt carbon (soot) is produced

Question 9

further substitution

Answer 9

• CH3. more reactive ( 2,4,6)
• OCH3
• OH
• NH2
• NO2. less reactive ( 3,5)
• COCl

halogens
withdraw electrons but substitution to the 2,4 position

Question 10

Nitration

Answer 10

important step in synthesis, including the manufacture of explosives and formation of amines
(Electrophilic attack on benzene rings results in substitution, limited to monosubstitutions)