CH 8-1 Electrophilic Addition of HX

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Presentation transcript:

CH 8-1 Electrophilic Addition of HX 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).