Orgo 3 - 6 loudon

The addition of a proton to the double bond of an alkene results in a product with the acidic proton bonded to the carbon atom that already holds the greater number of hydrogens.


extended: In an electrophilic addition to the alkene, the electrophile adds in such a way that it generates the most stable intermediate.

-- This rule applies to reactions between alkenes and other electrophiles as well

reactive intermediates

The complete description of a reaction pathway, including any reactive intermediates, that describes electron movement, the energy profile, kinetics, orbital descriptions, and stereochemistry

1. The e- pair in alkene is donated to the proton in H-X. The resulting species is called a carbocation.

2. The halide ion (X-) is a nucleophile and donates a lone pair of electrons to the electron deficient carbocation (electrophile) forming a new bond.

(Markovinikov)

primary < secondary < tertiary

trigonal planar → sp2-hybridized

additive

The overlap of bonding electrons from the adjacent s-bond with the unoccupied p-orbital of the carbocation (NOT formation of a covalent bond)


is an additional factor of stabilization for a carbocation.



can be shown w/ resonance structures

• 
• minor (Cl on 2°).           major (Cl on 3°)

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• 

represents an energy barrier to the interconversion between reactants and products

transition states are maxima in energy diagrams

very short lifetimes; partially formed bonds – impossible to observe


Forward and reverse reaction have same transition state (‡).

• 1. The energy barrier.
• 2. The Temperature (reactions are faster at higher temperatures ).
• 

The slowest step in a chemical reaction; controls the reaction rate.

      * corresponds to the highest energy barrier

says that a transition state more closely resembles whichever of the two states on either side of it is closest to the transition state in energy. If there’s an intermediate, this is usually closest in energy to the TS.