Colour by Design - Aromatic Molecules

Question 1

what is kekule’s structure of benzene?

Answer 1

suggested benzene was a 6 membered carbon ring with alternating single and double bonds

shape was asymmetrical hexagonal planar

Question 2

what were the strengths of kekule’s model of benzene?

Answer 2

agreed with most observations

Question 3

what were the issues with kekules model of benzene?

Answer 3

predicted the wrong enthalpy of hydrogenation of benzene

benzene unreactive with bromine water - according to kekule it should’ve reacted

has a regular shape - in kekule double + single different lengths

actually symmetrical hexagonal planar

Question 4

what was kekule’s expected value of the enthalpy of hydrogenation of benzene?

Answer 4

3 times the value of cyclohexene as it has 3 times the no. double bonds

Question 5

what is the actual value of the enthalpy of hydrogenation of benzene compared to kekules expected value?

Answer 5

much lower so it is more stable than predicted

Question 6

draw kekule’s shape of benzene

Answer 6

Question 7

what is the delocalised model of benzene?

Answer 7

suggests that carbon p-orbitals perpendicular to the ring overlap and form circular π-orbitals above and below the ring, containing 6 electrons

the electrons are delocalised because the orbitals overlap

Question 8

how does delocalisation affect the stability of molecules?

Answer 8

as a general rule:

more delocalised = more stable

Question 9

when is ‘phenyl’ used to name arenes?

Answer 9

when a benzene residue is attached to another molecule

it represents C₆H₅ aka benzene residue

Question 10

what are feedstocks?

Answer 10

reactants that go into a chemical process

Question 11

what are the conditions for a molecule to be aromatic?

Answer 11

contain a benzene ring

are cyclic

are planar

have 4n+2 delocalised electrons

Question 12

what are the conditions for aromatic molecules to be delocalised?

Answer 12

atoms must all have available p-orbitals perpendicular to ring

p-orbitals overlap - allowing electrons to delocalise

Question 13

how does delocalisation of electrons affect the reactivity of a molecule?

Answer 13

the more delocalised electrons -> the more stable the molecule as more energy required to break delocalisation

Question 14

what are the characteristics of aromatic molecules?

Answer 14

Contain a benzene ring (or similar delocalised system)

Strong smell

The delocalised section is less/unconventionally reactive