Transcript CH 8-1 Power Point

Chapter 8: Electrophilic Addition of an
Electrophile (E+) and Nucleophile to Alkenes
CH 8-1 Electrophilic Addition of HX
(1) Electrophilic Addition of HX (HCl & HBr)
-What is an “electrophile”?
-Carbocation mechanism (rearrangements possible)
-Regioselective: “Markovnikov’s Rule”
-Non-stereospecific reaction
(2) Electrophilic Addition of H2O and ROH
-Acid catalyzed
-Carbocation mechanism (rearrangements possible)
(3) Electrophilic Addition of Br2 and Cl2
-”Halonium ion” mechanism
-No carbocation
-Stereospecific reaction
Electrophilic Addition of an Electrophile (E+)
and Nucleophile to Alkenes
•Electrophile (E+): an electron deficient atom (“Lewis Acid”)
•E+ must have a d+ or full positive charge
•E+ is always paired with a nucleophile (Nuc)
•Alkene sp2 carbons labeled d- (least substituted) and d+
(most substituted)
•Regioselective Reaction (Markovnikov Addition):
•E+ is attracted to the d- carbon (pi electrons “grab” E+)
•Nuc is attracted to and “grabs” the d+ carbon
Electrophilic Addition of an Electrophile (E+)
and Nucleophile to Alkenes
(1) Electrophilic Addition of HX (HCl & HBr)
-Carbocation mechanism
-Regioselective: “Markovnikov’s Rule”
-Non-stereospecific reaction
-Rearrangements possible
(2) Electrophilic Addition of H2O and ROH
-Acid catalysis
-Carbocation mechanism
-Rearrangements possible
(3) Electrophilic Addition of Br2 and Cl2 to alkenes
-”Halonium ion” mechanism
-No carbocation
-Stereospecific reaction
Electrophilic Addition of an Electrophile (E+)
and Nucleophile to Alkenes
(1) Electrophilic Addition of HX (HCl & HBr)
-Carbocation mechanism
-Regioselective: Markovnikov’s Rule
-Non-stereospecific reaction
-Rearrangements possible
Electrophilic Addition of HX: non-Stereospecific
•The electrophile adds randomly to either side of the
double bond, and nucleophile to either side of carbocation:
•Random addition produces all possible stereoisomers: in
this case a Racemic Mixture of enantiomers (50:50 mix).