aromatic nucleophiles

Question 1

what is the evidence for addition-elimination reaction in SeAr

Answer 1

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

Question 2

How is isotope effect shown in SeAr

Answer 2

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

Question 3

what is the evidence of the whealand intermediate in SeAr

Answer 3

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.

Question 4

what are the reagents and conditions for nitration of benzene

Answer 4

c.HNO3 and c.H2SO4

Question 5

what are the reagents and conditions on sulfonylation

Answer 5

cH2SO4 with SO3

Question 6

is sulfonylation under kinetic or thermal control

Answer 6

below 80*c is irreversible so kinetic control

High temps becomes reversible so thermodynamic control

Question 7

what are Rs and C for halogenation of benzene

Answer 7

halogen molecule and lewis acid
Br2 + FeBr3
Cl2 + AlCl3

Question 8

what are Rs and Cs for friedel-crafts alkylation

Answer 8

alkyl acid + lewis acid

eg RBr + FeBr3

Question 9

what are limitations to friedel-crafts

Answer 9

Carbocations often rearrange

products are electron rich relative to starting materials leading to poly-alkylation

Question 10

what are Rs and Cs for friedel-crafts acylation

Answer 10

acid chloride (anhydride) + lewis acid
for electron rich aromatics no lewis acid requiered

Question 11

why would friedel-crafts acylation be preferred over alkylation

Answer 11

It can be followed by carbonyl reduction and avoids rearrangement and over alkylation

Question 12

what are the activating o,p groups

Answer 12

NH2, OH, OR, R, benzene, amide

Question 13

what are deactivating o,p director groups

Answer 13

halides and H

Question 14

what are deactivating m director groups

Answer 14

aldehyde, ester, carboxylic acid, CN, NO2, N+R3 , SO3H

Question 15

is electrophilic addition under kinetic or thermodynamic control

Answer 15

kinetic control fastest product formed predominated formed via lowest energy TS

Question 16

how do the meta deactivating groups work

Answer 16

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

Question 17

how do the O,P activating groups work

Answer 17

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

Question 18

why is there a 1:1 ortho para ratio rather than expected 2:1

Answer 18

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

Question 19

give example of ipso-directing groups

Answer 19

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