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Lecture 19

CHM136H1 Lecture Notes - Lecture 19: Electrophilic Addition, Butene, Carbocation

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Tutorial Questions
Large emphasis on reactions
Alkene Reactions
Reaction Diagrams
Reaction Stereochemistry
Lecture Topics:
Pre-Lecture Notes:
Lecture Notes
Measuring Alkene Structures
Cis-2-butene for ex is more stable than trans
Equilibrium constant between cis/trans isomers
Reaction can give the difference of enthalpy, and thus free energy
Allows one to determine which form is thermodynamically more stable
For Butene, for example (Z,E,1-) - all go to saturated forms after hydrogenation
"Prefers" alkyl bonding over hydrogenation bonding
Finding: the more substituted double bonds are more stable
Electrophilic Addition of HX to Alkene
Reaction bw ethene with HBr, for example, breaks the double bond
X is usually Cl, Br, I, or OH
Almost 100% 2-bromopropane, very little of 1-bromopropane
This reaction is regioselective: constitutional isomer products possible, but only one
dominates the product solution
Propene with HBr: two isomeric products are possible (below)
H attaches to C with most Hs
X attaches to C with least Hs
Markovnikov's Rule: In electrophilic addition of HX to Alkene
"The H atom bonds faster to form the more stable carbocation intermediate than it
does to form the less stable carbocation"
Rule makes sense in the light of carbocation - it's more stable
More highly substituted carbocations are more stable (lower in E)
ie 3° carbocation is more stable than only hydrogens attached
Inductive Effect: substituents donate e- density to C+, stabilizing it
Products created in this manner are called "Markovnikov Products"
Markovnikov's Rule occurs because 2° carbocation is more stable than 1°, shown below
Most important point: Reaction favours carbon center connected to more carbons
Feb. 29/16: Lecture 19
February 29, 2016
12:09 PM
CHM138H1 Notes Page 1
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