ch 17: reactions of aromatic compounds Flashcards
(52 cards)
what type of reactions can occur with aromatic compounds?
electrophile aromatic substitution
electrophilic aromatic substitution
H gets replaced by an electrophile
draw out the mechanism for electrophilic aromatic substitution
1.generation of electrophile
2. addition of electrophile to form a resonance stabilized carbocation
3. deprotonation with base to re-form the aromatic system
what happens to the carbon with the substituent on it now?
it is a sp3
halogenation
benzene reacts with Cl2 or Br2 in the presence of FeCl3 or FeBr3
why are I2 and F2 not used?
I2 is unreactive and F2 reacts too violently
nitration and sulfonation
adding nitro or sulfonic acid groups onto an aromatic ring using EAS
reagents for nitration and sulfonation
H2, Pd-C or Fe, HCl, or Sn, HCl
what will a substituent influenct in reactions of electrophilic aromatic substitution
rate and orientation
rate
a substituted benzene may react faster or slower than benzene itself
orientation
if only one group is added, it could be ortho, meta, or para to the existing substituent
what determines the position of the incoming substituent?
the identity of the existing substituent
what kind of group is an ortho, para director?
alkyl group
why are alkyl groups ortho, para-directors?
they have an electron donating inductive effect which stabilizes the carbocation intermediate if attack occurs at one of those positions
is the ortho/para energy higher or lower than benzene in presence of an alkyl group?
lower (kinetic product)
what is an alkyl group referred to as when talking about ortho and para?
ortho, para director
what are substituents with lone pairs on connected atoms considered? and why?
ortho, para director because the carbocation intermediate has additional resonance stabilization upon o- or p- attack
example of lone pair ortho/para director
OCH3 or NH2
activators
substituent on the ring is electron donating, the ortho/para position are activated
deactivators
if the substituent group is electron withdrawing, the ortho and para positions are deactivated
meta-directing groups
electron withdrawing groups activate the meta product
- example: NO2
why do meta directors occur?
attack at an ortho or para position would give a destabilized carbocation
ortho-para directing activators
give ortho/para products and react faster than benzene
examples of ortho/para directors
- NH2, NHR, NR2
- OH
- OR
- NHCOR
- R
