B6 organics 2 Flashcards
Which model of benzene is this?
Kekulé’s model
Which model of benzene is this?
Delocalised model
Describe the structure and bonding in Kekulé’s model of benzene.
P-orbitals overlap to form pi-bonds. Pi-electrons are localised between carbon atoms. Alternating pi-bonds.
What is the similarity between Kekulé’s benzene model and the delocalised benzene model?
Both have overlap of p-orbitals.
Describe the delocalised model of benzene.
P-orbitals overlap to form pi-bonds, with pi-electrons delocalised into delocalised ring pi-system.
What is the evidence to suggest that Kekulé’s model of benzene isn’t correct?
Carbon-carbon bond lengths are all the same size in benzene, but not in Kekulé’s model. Enthalpy of hydrogenation of benzene is less exothermic than Kekulé’s model. Benzene is less reactive than alkenes - bromination requires a catalyst for benzene but not for alkenes.
Name this molecule.
Phenylamine
Name this molecule.
Benzonic acid
Catalyst for benzene electrophilic substitution - nitration.
Concentrated Sulfuric Acid
Conditions for benzene electrophilic substitution - nitration, and why.
Less than 50°C to prevent further substitutions occurring.
Inorganic product for benzene electrophilic substitution - nitration.
Water
Electrophile generator step for benzene electrophilic substitution - nitration.
Mechanism step for benzene electrophilic substitution - nitration.
Catalyst regeneration step for benzene electrophilic substitution - nitration.
Catalyst for benzene electrophilic substitution - halogenation.
Halogen carrier - AlCl3 or FeCl3
Inorganic product for benzene electrophilic substitution - halogenation.
Hydrogen halide
Catalyst generation for benzene electrophilic substitution - halogenation.
Mechanism for benzene electrophilic substitution - halogenation.
Catalyst regeneration for benzene electrophilic substitution - halogenation.
Reactant for Friedel-Crafts alkylation.
Haloalkane
Catalyst for Friedel-Crafts alkylation.
Halogen carrier - AlCl3 or FeCl3
Inorganic product of Friedel-Crafts alkylation.
Hydrogen halide
Reactant of Friedel-Crafts acetylation.
Acyl chloride
Catalyst for Friedel-Crafts acetylation.
Halogen carrier - AlCl3 or FeCl3
Inorganic product of Friedel-Crafts acetylation.
Hydrogen halide
Structure of acyl chloride.
Describe and explain why benzene is more resistant to bromination than alkenes.
In alkenes, electrons in the pi-bond are localised between carbon atoms. In benzene, electrons in the pi-bond delocalise into the delocalised ring pi-system. Alkenes therefore have a higher electron density, so can polarise electrophiles more, making them more susceptible to electrophilic attack.
Structure of phenol.
How to determine whether a molecule is a phenol or an alcohol.
-OH must be directly bonded to the benzene ring to be a phenol. Otherwise, properties will be that of an alcohol.
Evidence to prove that phenols are weak acids.
Will react with NaOH (Strong base). Will not react with carbonates (weak base).
How to test for the presence of a phenol in a compound.
No reaction with carbonates, but reaction with strong bases (NaOH). Decolourises bromine water, and forms a white precipitate.
Observations of bromination of phenol.
Bromine water is decolourised. White precipitate forms.
Catalyst for phenol’s electrophilic substitution with bromine.
None
Equation for bromination of phenol.
Products of phenol’s bromination.
2,4,6-tribromophenol and 3HBr
Catalyst for phenol’s nitration.
No catalyst required
What shows that phenol is more reactive than bromine with its nitration reaction?
Dilute nitric acid not concentrated. No catalyst required.
What must all acids be in benzene’s electrophilic substitutions?
Concentrated
Reactant of benzene’s electrophilic substitution - nitration.
Concentrated nitric acid
Products of phenol’s nitration.
Mix of 2-nitrophenol and 4-nitrophenol
Equation of phenol’s nitration.
Describe and explain why phenol is more susceptible to electrophilic substitution than benzene.
Lone pair of electrons from oxygen in phenol partially delocalises into the delocalised ring pi-system. Therefore, electron density is higher than benzene, making the electrophile more polarised by phenol, which is more susceptible to electrophilic attack.
What are the 2- and 4- directing groups?
-OH and -NH2
What are the -3 directing groups?
-NO2
What directing group is -NO2?
3-
What directing group is -NH2?
2- and 4-
What directing group of -OH?
2- and 4-
