Aromatic Compounds Flashcards
1
Q
Describe, in terms of orbital overlap, the similarities and differences between the bonding on the Kekule model and the delocalised model of benzene
A
- both overlap of p orbitals
- both have pi bond / ring above and below bonding C atoms
- kekule has alternating pi bonds / 2 electrons in pi bond / overlap in one direction / localised
- benzene has pi ring / overlap in both directions / delocalised / all p orbitals overlap / 6 electrons in pi bond
2
Q
Evidence that supports the delocalised model of benzene
A
All C-C bond lengths are the same
Enthalpy of hydrogenation is less exothermic than expected
Benzene is less reactive than alkenes
Benzene does not decolourise bromine
3
Q
Why is phenol nitrated more readily than benzene
A
- in phenol, a lone pair of electrons on O is partially delocalised
- electron density increases
- more susceptible to electrophile attack
- phenol attracts / accepts electrophile
- electrophile more polarised
4
Q
Why are carbon - carbon bonds in benzene the same length
A
Pi bonds in benzene are delocalised
5
Q
2,4-directing groups
A
OH and NH2
6
Q
COOH group
A
electron withdrawing group
7
Q
NO2 - NH2
A
Sn/HCl
