CHEM 343 - Substitution and Elimination Reactions

SN1 Requirements

• A good leaving group attached to an sp3 carbon (includes Cl, Br, I, OTs, OMs, and Otf, H2O, and sometimes ROH)

• Stabilized carbocation (3ºC > 2ºC >> 1ºc >>> Me

• Nucleophile must be a weak base or non basic (includes Br, Cl, I, H2O, ROH, N=N=N, RSH)

SN2 Requirements

• A good leaving group attached to an sp3 carbon (includes Cl, Br, I, OTs, OMs, and Otf, H2O and ROH may or may not work)

• Unhindered alpha carbon (Me > 1ºC >> 2ºC >>>> 3ºC)

• A good nucleophile with lots of e- density, tend to be basic (includes Cl, Br, I, MeO, OH, phenolate, carboxylate, alkoxide, thiolate, HS, C3SO, azide, cyanide, thiol, NR3, RNH2, NH3)

E1 Requirements

not yet available

E2 Requirements

• A good leaving group attached to an sp3 carbon (includes Cl, Br, I, OTs, OMs, and Otf)

• Moderate to strong base depending on hindrance of C,

  • Moderate bases (conj. pka ~ 10) do E2 when C is too hindered for SN2

  • Strong bases (conj. pka ~≥ 15) otherwise

• Need an antiocoplanar beta hydrogen