substitution Flashcards
how does substitution occur?
1. SN1
2. SN2
Are they exomthermic or endothermic
it is the reaction between l.g. and nu-
1. lg leaves first then nu- attacks
2. lg ‘s leaving and nu- add takes place simultaneously
Exothermic
Rate of SN1 is directly dependent on?
- R-X conc
- C+ stabilty before rearrangement
- X- stability
- presence of EWG(stronger the ewg quicker and easier will be the rds step)
since it is the rds step in SN1 .i.e. R-X–> R+ + X-
how does nature of substrate effect rate of SN1
substituted benzylic>3RX>benzylic>allylic
R-X -3 º > 2 º > 1 º
nature of leaving group effect in SN1
(same for SN2)
better lg=>more rate
R-I > R-Br > R-Cl > R-F
nature of solvent where Sn1 if favoured
pps
it solvates both R+ AND X-
nature of solvent where Sn2 if favoured
paps
attack in SN1 takes place from which side
practically, IOC
theoretically, IOC%=ROC%
ROC= FRONT(not rear) IOC=BACK(inversion)
basic difference b/w SN1 and SN2
SN1- C+ stability, becuz R+ rds mein banta hai
SN2- less steric hinderance becuz one step process, nu- tabhi lagega agr crowding na ho rahi ho
SN2 roc or ioc
Always IOC(back side), to avoid steric hinderance
Rate of SN2 depends upon
- Stability of T.S.
- EWG
- Nu- Concn.
Nature of substrate in R-X in SN2
R-X: 1 º > 2 º > 3 º
Rate of SN2 @hinderance
unhindered> α hindered> βhindered
R-X + NaI(acetone) gives
R-I +NaX
Finklestein reaction SN2
R-X + [AgF, HgF2, SbF5]MF- gives
R-F + MX
ETHER* [R1-O-R2 ]* + H2O/H+(acidic hydrolysis)
R1-OH + R2-OH