Ch. 16 – Reactions of Aromatic Compounds Flashcards
Does benzene act as an electrophile or a nucleophile?
nucleophile (has lose pi electrons that are delocalized)
What type of general reactions are favored for benzenes? Hint: aromaticity
those that keep the aromatic ring intact
What is electrophilic aromatic substitution?
H atom on benzene is replaced by an electrophile (+E)
How many steps does the general mechanism for electrophilic aromatic sub have? What are they?
2 steps
1) add E+ to benzene (forms carbocation)
2) base deprotonates to reform aromatic molecule
How many resonance structures are given when C+ is formed by the addition of E+ to benzene?
3 res structures where carbon w/ E is sp3 hybridized
What is a sigma complex?
resulting carbocation structure after adding E to benzene ring
What is the RDS is EA sub?
addition of E+ because molecule loses aromaticity
Where is positive charge on EA resonance structures always located?
either in ortho or peta positions
How do groups on ortho/peta carbons affect Ea in formation of carbocation intermediate in EA sub?
groups that stabilize positive charge will drop Ea
groups that destabilize positive charge will increase Ea
What is the active electrophile in halogenation of benzene?
Lewis acid-base complex
What product does FC alkylation of benzene give?
alkyl benzene
What product does FC acylation of benzene give?
ketone
In FC alkylation of benzene, which R-Cl types give carbocations?
2º and 3º only
What type of electrophile does acylation produce?
acylium ion
Do vinyl and aryl halides react with FC alkylation?
No because their carbocations are highly unstable
Can carbocation RAR occur for FC alkylation?
yep, hydride shift
What forms from intramolecular FC reactions?
forms new ring (will be double ring)
Can carbocation RAR occur for FC acylation?
no RAR
What causes inductive effects?
electronegativity of atoms in the sub and polarizability
If an atom is more EN than carbon (inductive), what happens to electron density?
pulled out of benzene
If a polarizable alkyl group (X is in a pi system) is on benzene (inductive), what happens to electron density?
donated to benzene
How does p character effect electronegativity?
more p character = more EN
What are resonance effects?
donation or withdrawal of electrons depending on if they put positive or negative charges on benzene
How can you tell if res structures donate or withdraw electron density?
donate if neg charges result on benzene
withdraw if pos charges result on benzene
What groups are always electron donating?
alkyl (R) groups, O, N groups
What groups are always electron withdrawing?
halogens (X), double bond, Y with full or partial pos charge
What groups are ortho/para directors and activators?
alkyl and O/N groups
What group is ortho/para deactivators?
halogens
What groups are meta directors and deactivators?
Y with double bond or partial/full pos charge
What are activators?
subs on benzene that make it react faster
What are deactivators?
subs on benzene that make it react slower
What makes an activator/deactivator?
RDS accounting for formation of carbocation
activators = electron donating groups because they stabilize carbocation
deactivators = electron withdrawing groups because they destabilize carbocation
What is the one group that follows inductive effects over resonance effects?
halogens
