HO− + HOR +
Nucleophile Alkyl halide Alcohol Leaving group
R X X −
2) General Reaction for Nucleophilic Substitution of an Alkyl Halide by Water
HO HOR
HH
HOR
H 2 O
H 3 O+
+ + +
Nucleophile Alkyl halide Alkyloxonium ion
+ +
X −
X −
R X
i) The first product is an alkyloxonium ion (protonated alcohol) which then loses
a proton to a water molecule to form an alcohol.
6.5 LEAVING GROUPS
- To be a good leaving group the substituent must be able to leave as a relatively
stable, weakly basic molecule or ion.
- In alkyl halides the leaving group is the halogen substituent –– it leaves as a
halide ion.
i) Because halide ions are relatively stable and very weak bases, they are good
leaving groups.
- General equations for nucleophilic substitution reactions:
Nu − + R L R Nu + L−
or
Nu + R LR Nu+ + L−
Specific Examples:
