CH 6 & 7 - Substitution and Elimination Reactions

NaOH (sodium hydroxide)

SB, SN, unhindered

H2O (water)

WB, WN, unhindered

CH3OH (methanol)

WB, WN, unhindered

CH3CH2OH (ethanol)

WB, WN, unhindered

CH3CH2ONa (alkoxide)

SB, SN unhindered

NaH (sodium hydride)

SB, SN, unhindered

NaNH2 (amide)

SB, SN, unhindered

NH3+ (ammonia)

WB, WN, unhindered

NaSH

WB, SN, unhindered

(CH3)3COH (tert-butanol)

WB, WN, hindered

(CH3)3COK (alkoxide)

SB, WN, hindered

LDA

LiN(i-Pr)2

SB, WN, hindered

CH3CO2Na (carboxylate)

WB, SN, unhindered

CH3CO2H (acetic acid)

WB, WN, unhindered

KCN (potassium cyanide)

WB, SN, unhindered

NaCCH

SB, SN, unhindered

Major possible mechanisms for methyl LG

Sn2

Major possible mechanisms for 1º LG

Sn2 / E2

Major possible mechanisms for 2º LG

Sn2 / E2

Major possible mechanisms for 3º LG

Sn1 / E1 OR E2

Good leaving groups

Cl, Br, I

Weak nu-/weak base

Sn1 or E1 depending on temperature

Strong nu-/strong base, if 1º

Sn2

Strong nu-/strong base, if 2º or 3º

E2

Strong nu-/weak base, if 1º or 2º

Sn2

Weak nu-/strong base

E2

Sn2

Must be strong nu-

Must be 1º or 2º

Inversion of configuration required

Bimolecular rate law

Sn1

Weak nucleophile

Weak base

Must be 2º or 3º

Temp <25 ºC

Racemic mixture R/S (two products if original substrate is chiral)

Unimolecular rate law

E1

Weak nucleophile

Weak base

High temperature required (<50 ºC)

2º or 3º

Elimination - no steriochemistry concerns - create double bond

E2

Strong base

2º or 3º

Temperature possible

Aprotic solvent

Surrounds + charge

Good for Sn2

Strong nucleophile won't want to be surrounded by solvent

Protic solvent

Surrounds - charge

Good for Sn1