Alcohols: Substitution and Elimination

Leaving Group. Can be easily converted to a good LG.

HO^- is a very poor

Acid (HCl, HBr, HI), SOCl₂ or PBr₃, convert to sulfonate ester

3 ways to make a good Leaving Group

Protonate (OH bad LG to good LG), LG leaves, forms carbocation (check for rearrangements), combine with Nu (S_N1 - HBr/HI/HCl) OR lose a β-proton (E1 - H₂SO₄)

ACID S_N1/E1 (2° or 3°)

Protonate, Nu attack of back side (walden inversion). Great for HBr and HI, HCl needs help.

S_N2 (1° or CH₃OH)

O attacks S (Attack). LP moves back down an O to make a double bond, kicking off a Cl atom (loss of LG). Pyr LP attacks proton on the O atom and removes it (Proton off). Cl- attacks from the backside of the O atom, pushing OSOCl off, makes Cl a dash bc it attacked from the back (S_N2 attack)

SOCl₂

O attacks P (S_N2 attack), one Br leaves, then Br attacks backside of O atom (S_N2 attack/LG)

PBr₃

mechanism is similar to SOCl2 (pyr scavenger). O attacks the sulfonate (TsCl, MsCl, or TfCl). An O atom apart of the sulfonate group moves it’s l.p. down and pushes Cl off. Pyr comes in to pull H off the original O atom. Leaves you with a compound that can go through Nu/S_N2

Sulfonate Ester

TfCl

TsCl

MsCl