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Reactions of alkenes and alkynes (Electrophilic addition reactions of…
Reactions of alkenes and alkynes
Electrophilic addition reactions of alkenes
& alkynes
Reaction mechanism
Markovnikov’s rule: When unsymmetrical alkene adds
to unsymmetrical reagent, the positive portion of the reagent (eg. Hd+) adds to the carbon of C=C (in alkene) that is less substituted (the carbon of C=C with more H) to give the more stable carbocation
Major product = H adds to the carbon (on C=C) with more H
(Affected by) Carboncation (carbon atom with 3 bonds and a positive charge) Stability
depends on the groups directly attached to the C+
Alkyl [R groups (R ¹ H, R = methyl, ethyl etc.) are electron-releasing groups and stabilize the carbocation.
The more R group attach to C+, the more stable is the carbocation thus more favorable to be formed
Reactions in General: Alkene and reagent (A – B) added together, the pi bond in alkene is broken to form one saturated product.
3 examples
Addition of halogens – Halogenisation
Addition of water – Hydration
Addition of hydrogen halide
Chemical bonds
In alkene the C=C contains 1 s bond and 1 p bond
In alkynes the CºC contains 1 s bond and 2 p bonds
In...
p bond, the electrons are loosely held and the electron cloud is projected away from the bonded atoms which is accessible for reaction
p electrons C=C and CºC bonds are available to donate to electron poor species
C=C and CºC are nucleophile (electron rich)
s bond, the 2 electrons are tightly held between the bonded atoms and not accessible for reaction
