nucleophilic aromatic substitution

Question 1

list the 3 criteria for making the aromatic ring function as an electrophile

Answer 1

• ring must have a strong electron withdrawing group
• must be a leaving group that can leave
• LG must be o/p to the electron withdrawing sub

Question 2

what is the name of the reaction to make the ring electrophilic

Answer 2

addition-elimination (SnAr)

Question 3

T or F: the SnAr reaction is concerted

Answer 3

true

Question 4

describe the SnAr reaction

Answer 4

nucleophile comes to the electrophilic carbon and the electron density around the carbon moves, but the LG doesn’t leave. We get a Meisenheimer complex (intermediate), and then the LG leaves which gives us our product

Question 5

why doesn’t SnAr reaction work if the LG is meta to the electron withdrawing sub

Answer 5

we only get three resonance contributors in the intermediate, and we need four or else the charge never leaves the ring

Question 6

how is elimination-addition different from addition-elimination (SnAr)

Answer 6

we eliminate and then add the nucleophile. It’s still putting a nuc on benzene, but we use a different mechanism

Question 7

describe the elimination-addition mechanism

Answer 7

nuc attack on benzene = benzyne is formed. Then the nuc attacks the triple bond to give us two possible products

Question 8

what is the major product for the elimination-addition reaction

Answer 8

major product is the nuc in the spot where the LG was