Aromatic Compounds Flashcards
Why do benzene molecules not undergo typical alkene reactions?
Resonance -> delocalisation of electrons around the ring increases stability
Name a benzene ring with a methyl group attached
Toluene
How do you name disubstituted benzene?
Ortho 1,2
Meta 1,3
Para 1,4
What reactions do benzene rings undergo?
Electrophilic aromatic substitution
What are the steps to electrophilic aromatic substitution?
Electrophilic attack -> a pair of electrons from the benzene ring are donated to the electrophile
This forms a number of resonance stabilised cation s with the cation on the ortho and para positions relative to the electrophile bonded carbon -> resonance hybrid
Elimination occurs as the electrons from the C-H bond are donated to the ring and the H leaves
What is the reactivity of benzene ring?
Benzene is unreactive because it has many resonance stabilised cation intermediate forms
What are electrophiles that can cause electrophilic aromatic substitution?
Halogen - Cl+, F+, Br+
Nitro group - NO2+
Ketone group - RCO+
Alkyl groups
How do you form halogen electrophile?
Cl - Cl + FeCl3 -> Cl+ + FeCl4-
Heterolytic bond cleavage of the Cl2
How do you form nitro group- electrophile?
HNO3 + H2SO4 -> NO2+ HSO4- + H2O
What is friedel-crafts acylation?
Use of AlX3 to generate a ketone group (electrophile) to add on to benzene ring
What is friedel-crafts alkylation?
Use of AlX3 to generate an alkyl group to add on to benzene ring
What happens when you mix a primary alkyl halide and AlCl3?
The primary carbocation rearranges to form secondary -> positive inductive effect ie distribution of charge means secondary carbocation is more stable
What are the reagents to go from benzene to nitrobenzene?
HNO3/H2SO4
What are the reagents to go from benzene to alkylbenzene?
AlkylCl + AlCl3
What are the reagents to go from benzene to halogen substituted benzene?
X2 + FeX
What are the reagents to go from nitrobenzene to aniline?
Fe/H+
Then NaOH
What are the reagents to go from aniline to diazonium ion?
Add HNO2
at 0 degrees celsius
How do you form phenol from benzene ring?
Benzene
Add HNO3/H2SO4
Nitrobenzene
Add Fe/H+ then OH-
Aniline
Add HNO2 at 0C
Diazonium ion
Add H3O+
Phenol
How do you form benzonitrile?
Benzene
Add HNO3/H2SO4
Nitrobenzene
Add Fe/H+ then OH-
Aniline
Add HNO2 at 0C
Diazonium ion
Add CuCN
Benzonitrile
How do you go from nitrile to carboxylic acid?
Add acid or base
What are the factor to consider when determining the position of the substituent groups of a disubstituted benzene?
Where does substitution occur initially -> ortho, meta, para
Will the reaction occur more or less readily than for the same electrophile with benzene -> is the first substituent group activating or deactivating
How do you determine to what position the second substituent of a benzene ring will be added to?
Consider whether the group is activating or deactivating
Activating -> electron donating (species with lone pair for donation into the ring + alkyl groups for induction)
Deactivating -> electron withdrawing (sp2 carbons with polar bond)
If activating -> ortho, para more likely
If deactivating -> meta more likely
Consider the number of reasonable resonance contributors for carbocation intermediate -> postively charged species cant be together
More number = more stable = more likely to form
