SN1 SN2 E1 E2

Video

Base, Nucleophile	Methyl Alkyl Halide	Primary Alkyl Halide	Secondary Alkyl Halide	Tertiary Alkyl Halide
Strong, Strong	SN2	SN2	(E2 Major Zaistev)(SN2 Minor)	E2 Zaistev
Strong, Weak	SN2	E2	E2 (Small → Zaistev)(Bulky → Hofmann)	E2 (Small → Zaistev)(Bulky → Hofmann)
Weak, Strong	SN2	SN2	(Polar Aprotic Solvent → SN2)(Polar Protic Solvent → SN1)	SN1
Weak, Weak	SN2	Impractical SN2	(Low Heat → SN1)(High Heat → E1)	(Low Heat → SN1)(High Heat → E1)

Strong Base, Strong Nucleophile

• ${}_{}^{}{}_{}^{-}\mathrm{OH}$
• ${}_{}^{}{}_{}^{-}\mathrm{OMe}$
• ${}_{}^{}{}_{}^{-}\mathrm{OEt}$
• ${}_{}^{}{}_{}^{-}\mathrm{C}\equiv \mathrm{CH}$

Strong Base, Weak Nucleophile

• Small
  • $\mathrm{H}{}^{-}$
• Bulky
  • ${}_{}^{}{}_{}^{-}\mathrm{O}t\text{-}\mathrm{Bu}$

Weak Base, Strong Nucleophile

• ${}_{}^{}{}_{}^{-}\mathrm{Cl}$
• ${}_{}^{}{}_{}^{-}\mathrm{SH}$
• ${}_{}^{}{}_{}^{-}\mathrm{F}$
• ${}_{}^{}{}_{}^{-}\mathrm{Br}$
• ${}_{}^{}{}_{}^{-}\mathrm{N}{}_3$
• ${}_{}^{}{}_{}^{-}\mathrm{CN}$
• $\mathrm{NH}{}_3$
• $\mathrm{H}{}_2\mathrm{S}$

Weak Base, Weak Nucleophile

• $\mathrm{H}{}_2\mathrm{O}$
• $\mathrm{MeOH}$
• $\mathrm{EtOH}$

Notes

• Adding heat increases the likelihood of elimination over substitution
  • Based on the Gibb’s Free Energy equation, increasing $T$ will result in a more negative $\Delta G$ for reactions that have a higher $\Delta S$, and elimination increases entropy more than substitution since it produces multiple products
• Using protic solvents increases the likelihood of elimination over substitution, E1 over E2, and SN1 over SN2
  • The protic environment stabilizes the leaving group of E1 or SN1
• See Zaistev’s Rule and Hofmann Product for difference