electrophilic aromatic substitution

why is a lewis acid catalyst used for electrophilic substitution?

bromine must be activated by lewis acid (electron acceptor)

why is addition slow and elimination fast?

slow because breaking aromaticity

fast because restoring aromaticity

how does the lewis acid get involved in electrophilic substitution reaction (e.g. AlCl₃)

what are electrophilic substitution steps for Br₂ reacting with benzene?

what is the energy profile diagram of electrophilic substitution?

higher activation energy for first step as breaking aromaticity

what is the reaction for nitration?

how is the nitronium ion formed? (from HNO₃ and H₂SO₄)

what is the mechanism for nitration?

what is the sulfonation reaction?

mechanism for protonation of sulfur trioxide (SO₃ and H₂SO₄)

what is the mechanism for sulfonation?

what is the friedel crafts acylation reaction?

mechanism for formation of acylium ion (acyl chloride and AlCl₃)

friedel crafts acylation mechanism

what is the friedel crafts alkylation for tertiary alkyl chloride?

primary alkyl chloride friedel crafts alkylation

what is Clemmensen Reduction?

what is the conditions?

NaBH₄

what are the conditions?

H₂SO₄

what are the conditions?

H₂ / Pd

where is the ortho position?

where is the meta position?

where is the para position?

if X is an electron donating group, how does this affect electrophilic substitution reactions?

rate? position?

rate increases

happens preferentially at ortho and para

if X is an electron withdrawing group, how does this affect electrophilic substitution reactions?

rate?

positons?

rate decreases

happens preferentially at meta

where does electrophilic attack occur?

at carbons with highest electron density

what does a lower chemical shift mean?

more shielding

more electron density

more nucleophilic

does electron rich or deficient aromatics react faster?

electron rich reacts faster

show resonance of phenol

what does a higher chemical shift mean?

less shielding

less electron density

less nucleophilic

show resonance

how does positive charges (electron withdrawing) affect positions?

deactivates ortho/para

least deactivated is meta which is why reactions happen here

how do inductive electron withdrawing groups affect position?

activate/deactivate?

strongly deactivating and meta directing

meta most likely, then ortho

how do inductive electron donating groups affect position?

activating/deactivating?

weak activating and ortho/para directing

ortho most likely, then para

how do electron donating groups affect positive charge on ipso carbon?

what substitution position is favoured?

stabilises positive charge

ortho/para substitution favoured

how do electron withdrawing groups affect positive charge on ipso carbon?

what substitution position is favoured?

positive charge destabilised

meta substitution favoured

are halogens activating/deactivating?

what position do they direct?

deactivating

ortho/para directing

para more likely than ortho

why is N activating by resonance while Cl is not (when they are both deactivating by induction)?

N has better orbital overlap than Cl for lone pair donation

why is fluorobenzene more reactive than chlorobenzene?

fluorine lone pairs overlap better with benzene pi system than chlorine lone pairs

• more efficient at electron donation by resonance