1. SN1 vs. SN2 vs. E1 vs. E2
Factors affecting the type of reaction an alkyl halide undergoes include:
Type of alkyl halide
methyl, 1o, 2o, 3o, allylic or benzylic
Strength of nucleophile or base

2. SN1 vs. SN2 vs. E1 vs. E2
Guidelines for Predicting Products of Substitution and Elimination Reactions:
The strength of the nucleophile or base determines the order of the reaction.
SN2 and E2 reactions require strong nucleophiles (or bases)
SN1 and E1 reactions generally use weak nucleophiles (or bases)

3. SN1 vs. SN2 vs. E1 vs. E2 Nucleophilicity (nucleophile strength):
a measure of the rate at which a nucleophile attacks an electrophilic carbon of a standard substrate
A species with a negative charge is a stronger nucleophile than a similar neutral species:
nucleophilicity of base > conjugate acid
CH3O- > CH3OH

4. SN1 vs. SN2 vs. E1 vs. E2
Nucleophilicity decreases from left to right in the periodic table
look at the element with lone pair of e-
more electronegative elements hold on to electrons more tightly
OH- > F-

5. SN1 vs. SN2 vs. E1 vs. E2 Nucleophilicity increases from top to bottom
size increases
electrons held more loosely
polarizability increases
bond can begin forming when atoms are farther apart
I- > Br-
Polarizable: having electrons that can move more freely toward a positive charge

6. SN1 vs. SN2 vs. E1 vs. E2

7. SN1 vs. SN2 vs. E1 vs. E2
Example: Identify the stronger nucleophile in each pair. Explain why.
NH3 or NH2-
H2O or NH3
HS- or Cl-
PH3 or NH3

8. SN1 vs. SN2 vs. E1 vs. E2 Base Strength:
Weaker acids produce stronger conjugate bases.
CH3CH2OH CH3CH2O-
Strong acids produce weak conjugate bases.
HBr Br-
strong base
strong nucleophile
weak acid
Weak base
good nucleophile
Strong acid

9. SN1 vs. SN2 vs. E1 vs. E2
The presence of bulky groups on the nucleophile makes it less nucleophilic but a stronger base.
hinders approach to the electrophilic carbon - -
t-butoxide ion
hindered
strong base
weak nucleophile
ethoxide ion
unhindered
weaker base
stronger nucleophile

10. SN1 vs. SN2 vs. E1 vs. E2
Example: Identify the stronger base in each pair.
OH- or H2O
CH3OH or CH3O-
(CH3)3CO- or CH3O-
Water and alcohols are amphoteric. They can serve as either an acid or a base. Water and alcohols are weak acids and weak bases.

11. SN1 vs. SN2 vs. E1 vs. E2
Guidelines for Predicting Products of Substitution and Elimination Reactions:
The type of alkyl halide is important in determining the type of reaction:
Methyl halide: SN2 exclusively
1o halide:
SN2 with a strong nucleophile (favored)
E2 with strong base (sometimes)
SN1 or E1 are sometimes observed at high temperatures if rearrangement produces more stable carbonium ion

12. SN1 vs. SN2 vs. E1 vs. E2
Guidelines for Predicting Products of Substitution and Elimination Reactions:
The type of alkyl halide is important in determining the type of reaction:
3o Halides:
E2 with a strong base
SN1 and E1 with weak nucleophile or weak base

13. SN1 vs. SN2 vs. E1 vs. E2
Guidelines for Predicting Products of Substitution and Elimination Reactions:
The type of alkyl halide is important in determining the type of reaction:
2o Halides:
Mixtures of products are common
Strong base/nucleophile gives SN2 and E2
Weak base/nucleophile gives SN1 and E1

14. SN1 vs. SN2 vs. E1 vs. E2
Guidelines for Predicting Products of Substitution and Elimination Reactions:
Strong bulky bases favor E2 reactions.
t-butoxide ion
Good nucleophiles with limited basicity favor SN2 reactions.
Br- I-

15. SN1 vs. SN2 vs. E1 vs. E2
Example: Predict the product(s) and mechanism of the following reaction. If more than one product or mechanism is possible, explain which is/are most likely.

16. SN1 vs. SN2 vs. E1 vs. E2
Example: Predict the product(s) and mechanism of the following reaction. If more than one product or mechanism is possible, explain which is/are most likely.

17. SN1 vs. SN2 vs. E1 vs. E2
Example: Predict the product(s) and mechanism of the following reaction. If more than one product or mechanism is possible, explain which is/are most likely.