aromatic nucleophiles Flashcards
what is the evidence for addition-elimination reaction in SeAr
using D isotope effects. C-D bond slightly stronger than than C-H.
C-H is broke in RDS and using D slows down rate which proves in two step process
How is isotope effect shown in SeAr
In almost all SeAr reactions TS1 be the RDS and will not have C-D breaking so no D isotope effect
But very rare that TS2 is RDS and it does have C-D breaking So D isotope effect is observed
what is the evidence of the whealand intermediate in SeAr
1) react benzene with HF-SbF5/SO2FCl at 120*c and use HNMR
2) react 1,3,5-trimethylbenzene with HBF4 which will form white insoluble solid.
what are the reagents and conditions for nitration of benzene
c.HNO3 and c.H2SO4
what are the reagents and conditions on sulfonylation
cH2SO4 with SO3
is sulfonylation under kinetic or thermal control
below 80*c is irreversible so kinetic control
High temps becomes reversible so thermodynamic control
what are Rs and C for halogenation of benzene
halogen molecule and lewis acid
Br2 + FeBr3
Cl2 + AlCl3
what are Rs and Cs for friedel-crafts alkylation
alkyl acid + lewis acid
eg RBr + FeBr3
what are limitations to friedel-crafts
Carbocations often rearrange
products are electron rich relative to starting materials leading to poly-alkylation
what are Rs and Cs for friedel-crafts acylation
acid chloride (anhydride) + lewis acid for electron rich aromatics no lewis acid requiered
why would friedel-crafts acylation be preferred over alkylation
It can be followed by carbonyl reduction and avoids rearrangement and over alkylation
what are the activating o,p groups
NH2, OH, OR, R, benzene, amide
what are deactivating o,p director groups
halides and H
what are deactivating m director groups
aldehyde, ester, carboxylic acid, CN, NO2, N+R3 , SO3H
is electrophilic addition under kinetic or thermodynamic control
kinetic control fastest product formed predominated formed via lowest energy TS
how do the meta deactivating groups work
All withdraw electrons using inductive effect, nitro groups also use resonance to put electrons onto electronegative oxygen, meta positions ensure + charge is never on the ipso-carbon
how do the O,P activating groups work
LP donation into ring causing resonance
alkenyl,aryl - conjugation with ring e donated into ring
alkyl - sigma conjugation e density from C-H or C-C bond donated
why is there a 1:1 ortho para ratio rather than expected 2:1
para slightly more activated than ortho, steric effect as ortho is closer to substituent for electrophile to join, using large electrophile will increase para selectivity
give example of ipso-directing groups
can use SO3H as temp directing group,
react compound with oleum forming para product as SO3H is big,
react with compound to be directed
now react with dil H2SO4(aq) to remove SO3H