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
Elimination addition
addition of a group to a benzene without a NO2 group under high pressure and temperature (350 C)
What is the mechanism of EA
- proton transfer to create anion
- loss of a a leaving group that forms benzyne
- nucleophilic attack by added group
- proton transfer to restore aromaticity
What is the key intermediate of Electrophilic addition
benzyne
True or False?
The triple bond in the benzyne intermediate is not a true triple bond?
true, it is better explained as a di radical
O3, DMS splits a double bond and adds Os on the end
ozonolysis
Pcc/ Chromic acid
- with secondary and primary alcohols
- primary alchols can be oxidized to aldehydes by PCC
- secondary alchols can be oxidized to ketones by PCC or chromic acid
terminal alkyne + R2BH and H2O2
antimarkovnkov addition to create a aldehyde
H2SO4, H2O and internal alkyne
markonikov addition to produce ketone
Why are aldehydes more reactive than ketones?
Bc they do not have weakly activating aklykl groups on both sides like a ketone does
True or False?
With a strong nucleophile and good leaving group a nucleophilic addition reaction will occur
False, you need a poor LG so the mechansim can proceed
If you have a poor nucleophile what is needed to proceed with NA?
Acid catalysis to make the electrophile very strong
Hydrate
two hydroxyl groups attatched to the same C
Acetal
two ether groups attatched to the same C
What is the first part of acetal formation?
the formation of the hemiacetal
1. pt
2. nuc attack
3. pt
What is the main intermediate for NA?
A hemiacetal
What is the second part of acetal formation
formation of the acetal
1. pt
2. nuc attack
3. LLG
4. pt
Acetals can be used as — — if you want to selectivley reduce a C=O bond
blocking groups
primary amines make —-
imines
Secondary amines make —-
enamines
What is the key intermediate of imine formation?
carbinolamine
- neutral intermedaite
Mechanistic steps for formation of the imine intermediate (carbinolamine)
- nuc attack
- proton transfer
- proton transfer
Mechanistic steps to second part of imine formation
- proton transfer
- LLG
- proton transfer
The formation of thioacetals is directly analogus to what other process?
acetal formation
Thioacetals when treated with —- – will yield an alkane
Raney Ni
reagents: acid + dithiol and Raney Ni
Wolf Kishner reduction
Heat + base to completely remove/ reduce an imine
