Aromatic Compounds Flashcards
Describe, in terms of orbital overlap, the similarities and differences between the bonding on the Kekule model and the delocalised model of benzene
- 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
Evidence that supports the delocalised model of benzene
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
Why is phenol nitrated more readily than benzene
- in phenol, a lone pair of electrons on O is partially delocalised into ring
- electron density increases
- more susceptible to electrophile attack
- phenol attracts / accepts electrophile
- electrophile more polarised
Why are carbon - carbon bonds in benzene the same length
Pi bonds in benzene are delocalised
2,4-directing groups
OH and NH2
COOH group
electron withdrawing group
NO2 - NH2
Sn/HCl
Give an example of an organic reaction where sulphuric acid is a catalyst
Elimination of alcohols
Nitration of benzene
Esterification
Hydrolysis of esters
3- directing group
NO2
Explain neutralisation of carboxylic acid with NaOH
Phenol loses H+
And carboxylate ion gains H+
Why is this a good representation of benzene
Delocalised structure is more stable
Enthalpy of hydrogenation is less exothermic than -357
Why can carboxylic acid react with acid
Electron pair accepts H+
