Steric hindrance at the electrophilic carbon slows the S N 2 reaction. no S N 2

polar solvents especially good for S N 1 (OK for some S N 2) aprotic solvents (no H on O or N) cannot H-bond to Nu especially good for S N 2

Intramolecular Reactions (within one molecule) forms ring Intramolecular reactions that form 3, 5, and 6 membered rings are faster. (favorable entropy)

E1 has the same first step as S N 1 (carbocation formation). Some E1 always accompanies S N 1.

Fig. 9-8, p. 368

Table 9-11, p. 368

Methyl Substrates: CH 3 L S N 2 only Primary Substrates: RCH 2 L good for S N 2 with almost any nucleophile no S N 1/E1 can cause E2 with a sterically hindered strong base potassium tert-butoxide (KOt-Bu) The Competition between Elimination and Substitution

Secondary Substrates: R 2 CHL S N 2 favored with good Nu that is not too basic (especially in aprotic solvents) CH 3 CO 2 –, RCO 2 –, CN –, RS – E2 favored with strong bases HO –, RO – (NaOH, NaOEt) S N 1 favored by absence of good Nu in polar solvent often neutral or acidic conditions some E1 product is usually formed a solvolysis reaction

Tertiary Substrates no S N 2 (too hindered) E2 favored with strong bases HO –, RO – (NaOH, NaOEt) S N 1 favored by absence of good Nu in polar solvent often neutral or acidic conditions some E1 occurs

S N 2 and E2 favored over S N 1 and E1 by a strong base/Nu S N 2 is slowed by steric hindrance, but E2 is not strong base, strong Nu strong base means E2, not S N 1

S N 2 and E2 Stronger bases favor E2 over S N 2 stronger base weaker base

S N 2 and E2 higher temperatures favor elimination  G =  H - T  S SN2SN2 weaker bases less steric hindrance lower temperature E2 stronger bases more steric hindrance higher temperature