alcohol substitution and elimination

HCl, HBr, HI

• methyl: SN2

• primary: SN2

• secondary: SN1 (w/R) — rearrangement of carbocation, if possible

• tertiary: SN1

SOCl₂, pyr., PBr₃, pyr.

methyl: SN2

primary: SN2

secondary: SN2

tertiary: NR

H₂SO₄, heat

methyl: NR
primary: E2 (w/R) — double bond produced can rearrange by reacting with acid

secondary: E1 (w/R)

tertiary: E1

POCl₃, pyr., 0 C

• methyl: NR

• primary: E2

• secondary: E2

• tertiary: E2

general considerations — HX

• rate tertiary > secondary > primary suggests that secondary alcohols undergo SN1

• HI > HBr > HCl

• Lucas Test: ZnCl₂ often added to HCl to make rate faster

• primary alcohols only undergo substitution if heated

• fastest: tertiary alcohols

general considerations — SOCl₂ or PBr₃

• better method for replacing OH group with Cl or Br

• follows SN2, means inversion

• no rearrangements

general considerations — H₂SO₄

• rate tertiary > secondary > primary

• E1 follows Zaitsev

• primary alcohols isomerize once the alkene forms

• rearrangements possible

• very harsh conditions

• alkenes formed tend to react with H⁺ and more stable alkenes can result

general considerations — POCl₃

• force E2 conditions, no rearrangements possible

• pyridine acts as a base