Chapter 25 - Aromatic Compunds Flashcards
What are problems with the Kekulé model?
- Lack of reactivity with bromine
- Equal lengths of C-C and C=C bonds
- Less exothermic hydrogenation enthalpy (more stable)
What is the delocalised model of benzene?
- P-orbitals above and below the plane of benzene ring to form a planar ring
- Sideways overlap of p-orbitals to create delocalised ring of electron density above and below plane of benzene ring
When is the phenyl- prefix used?
Alkyl chain attached to benzene has:
- Functional group
- 7+ carbon atoms
What is the name of a benzene with a COOH functional group?
Benzoic acid
What is the name of a benzene with a NH2 functional group?
Phenylamine
What is the name of a benzene with a CHO functional group?
Benzaldehyde
What type of reaction does benzene undergo?
Electrophilic substitution
What is the temperature involved in the nitration of benzene?
50º
Why must a halogen carrier be present in reactions with benzene?
Delocalised π electrons creating a lower electron density in the C=C bonds of benzene so insufficient to polarise non polar molecule (e.g. bromine)
Why is phenol less soluble in water than alcohols?
Due to the non polar benzene ring
Why does phenol act as a weak acid?
When dissolved in water it partially dissociates forming a phenoxide ion and and proton (H+)
Phenol is _____ acidic than alcohols
Phenol is _____ acidic than carboxylic acids
More
Less
How to distinguish between a phenol and carboxylic acid?
- React with sodium carbonate (weak base)
- Phenol will NOT react but carboxylic acid will
Compare the reactivities of ethanol, phenol and carboxylic acid relative to the strength of bases?
Ethanol - no reaction with strong or weak base
Phenol - reaction with strong base
Carboxylic acid - reaction with strong and weak base
What is formed in the reaction of phenol with sodium hydroxide (strong base)?
Salt and water (neutralisation reaction)
Compare the reactivities of benzene and phenol?
- Reactions of phenol occurs more readily
- Lone pair of electrons from oxygen of -OH group donated into π system of phenol
- Higher electron density of benzene ring
- Stronger attraction of electrophile
What is the difference between the bromination of phenol as compared to benzene?
Phenol doesn’t require a halogen carrier
What is the difference between the nitration of phenol as compared to benzene?
Phenol doesn’t require concentration nitric acid and sulfuric acid. Only needs dilute nitric acid
What forms when phenol reacts with bromine
White precipitate
What are activating groups?
- Electron donating groups
- 2- and 4-directing groups
What are the 2- and 4-directing groups? (ortho and para)
- NH2
- OH
- Halogens (deactivating groups!)
What are deactivating groups?
- Electron withdrawing groups
- 3-directing
What are the 3-directing groups? (meta)
- CHO
- COOH
- NO2
