Quiz 4 Flashcards
How can you tell if a group is an activating group?
if you draw the resonance structures and find a negative charge within the ring
Activating groups
electron donating groups that increase the rate of electrophilic aromatic substitution
True or false
Most activators are ortho para directors?
True
If your substiuent on the ring is very small what can be said about the directing of an activating group
it may favor ortho over para bc there are more ortho positions and less steric hinderence to consider
Deactivating groups
ewg that lower the rate of EAS by making the ring less nucleophilic
If the resonance structures feature a — charge on the ring it is likely a deactivator
positive
Most deactivators are — directing
meta
Why are halogens the exception to the deactivating meta directing rule?
Bc they deactivate by induction, not by resonance
halogens are electron withdrawing by — and — — by resonance
induction, electron donating
a lp at the benzylic position that only participates in resonance inside the ring
strong activators
ex: oxygen
a lp at the benzylic position that can resonate both inside and outside the ring
moderate activator
ex: ester or amide with e- connected to ring
akyl chains that donate electron density via hyperconjugation, not resonance
weak activators
Examples of strong deactivators
NO2, CX3, any + charged N
Moderate deactivators
carboxylic acids, ketones, aldehydes, where the pi bond to an electronegative atom is part of the conjugation of the ring
Weak deactivators
halogens that are deactivators by induction, not resonance
If the directing effects of the substients on the ring do not agree how do you know what directing effects to follow?
You follow the directing of the strongest activator
Blocking group
a group that can be easily added and taken off to help control the placement of new substituents on a ring
ex: sulfonation is often used
True or false?
Nitration cannot be done on a ring that has a amide group attatched
false, nitration cannot be done on a ring that has a nitro or alcohol group attatched bc it will react instead of the ring
In what order should you place a methyl group and a nitrogroup on a ring
methyl group first bc friedel crafts will not react with a deactivated ring
wait to install deactivator last
Nucleophilic aromatic substitution (NAS)
ring acts as electrophile and is attacked by nucleophile
What are the three conditions for NAS
- must have nitro group/ strong deactivator
- must have good leaving group
- leaving group cannot be meta to nitrogroup, must be ortho or para
Mechanism of NAS
- nuc attack on ring
- Loss of a leaving group on ring
Meisenheimer complex
intermediate of NAS, resonance stabilized carbanion
the ewg during NAS acts as an electron density — —to kick off leaving group
holding place
