aromatic chemistry

Question 1

kekule structure

Answer 1

ring of six carbons with alternating single and double bonds
not accurate

Question 2

evidence that led scientists to doubt kekules structure

Answer 2

-benzene does not undergo electrophilic addition reactions instead it undergoes substitution reactions (to maintain delocalised electrons)
-enthalpy change less exothermic than expected when compared to enthalpy change for cyclohexane because benzene is ore stable ( due to ring of delocalised electrons)
-bond length of benzene is in between double and single bond length

Question 3

benzene structure

Answer 3

6 carbon with ring of delocalised electrons
each carbon has one unused electron so it becomes delocalised
it is shared between all other carbons in the benzene ring and causes it to be more stable by sharing electrons

Question 4

what molecule is benzene

Answer 4

planar

Question 5

benzene bonding

Answer 5

each carbon has 3 covalent bonds
spare electrons in p orbital overlap ( to form pi cloud)
delocalisation - delocalised ring - makes benzene more stable

Question 6

benzene shape

Answer 6

planar - trigonal planar layout - flat
hexagon/6 carbon ring, 120 bond angle
c-c bonds equal lengths/ c-c bond length between single and double bond

Question 7

benzene stability

Answer 7

-expected enthalpy change of hydrogenation of kekules = -360 kj/mol-1
-enthalpy change of benzene is less exothermic by 152 kj/mol-1
-benzene lower in energy than kekules/ benzene is more stable

Question 8

physical properties of arenes

Answer 8

benzene is a colourless liquid at room temperature
benzene has a BP of 353K similar to hexane
benzene has MP of 279K alot higher than hexane because benzene is a planar molecule and they can stack together very well in the solid state. so IDD forces are harder to break

Question 9

the reactivity of aromatic compounds

Answer 9

1-the ring is an area of high electron density due to the delocalisation
this means arenes react with electrophiles
2-the aromatic ring is very stable. Energy has to be put in to break the ring system. This means in almost all reactions the ring remains intact at the end of the reaction

Question 10

combustion of arenes

Answer 10

arenes are rarely burned because:
-arenes are extremely useful substances in pharmaceuticals and so burning the is wasteful.
-arenes are unsaturated undergo incomplete combustion.

Question 11

uses of nitrated arenes

Answer 11

they can be used to produce explosives
methyl benzene is nitrated 3 times to make TNT