aromatic electrophiles

Question 1

what is SnAr reaction mechanism and rate

Answer 1

mechanism: addition-elimination

rate = k[ArX][Y-] RDS does not involve departure of LG

Question 2

is SnAr kinetic or thermodynamic control

Answer 2

kinetic control so TS1 is RDS

Question 3

what type of groups are best for SnAr

what makes a good LG

Answer 3

electron withdrawing groups at ortha/para relative to LG

high electronegativity makes good LG

Question 4

what intermediate is formed in SnAr

Answer 4

Meisenheimer intermediate which is not aromatic but is stabilised by delocalisation

Question 5

rank order of reactivity of halides to use in SnAr

Answer 5

F&raquo_space; Cl > Br > I
ranked in electronegativity as pull e density out of ipsocarbon making it partially +ve allowing nu attack
Cl most commonly used, F is expensive and hard to prep

Question 6

how are diazonium salts formed

Answer 6

aniline reacted with nitrosonium salt

Question 7

how is nitrosonium salt formed

Answer 7

sodium nitrite with mineral acid eg HCl H2SO4 HBF4

Question 8

when and how does Sn1ar occur

what is the rate

Answer 8

when no Cu salts
N2+ leaves rings,  leaving sp2 carbocation
carbonation reacts with nu
Driving force is loss of N2
rate = k[ArN2+]

Question 9

how can terminal N of diazonium ion react

Answer 9

some soft nucleophiles react at terminal

Question 10

how are benzynes prepered

Answer 10

chlorobenzene reacted with KNH2 in NH3 forming benzyne which can react with NH3 forming 50/50 mix of ipso and cine (2 position0 aniline