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Organic Chemistry Chapter 3 Part II. Addition to Alkenes - Markovnikov’s rule-. Nanoplasmonic Research Group. Reactions of Alkenes: Addition. Electrophile Literally ‘ ELECTRON ’ lovers: electron-POOR reagents Positive ions or electron-deficient species Nucleophile

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organic chemistry chapter 3 part ii

Organic ChemistryChapter 3Part II

Addition to Alkenes

- Markovnikov’s rule-

Nanoplasmonic Research Group

reactions of alkenes addition
Reactions of Alkenes: Addition
  • Electrophile
    • Literally ‘ELECTRON’ lovers: electron-POOR reagents
    • Positive ions or electron-deficient species
  • Nucleophile
    • Literally ‘NUCLEUS’ lovers: electron-RICH reagents
    • Donate electrons to an electrophile




E Nu

markovnikov s rule
Markovnikov’s Rule

The RULE says “The addition of a protic acid such as H-X to an alkene, the acid hydrogen (H) becomes attached to the carbon atom with the greatest number of hydrogens, and the halide (X) group becomes attached to the carbon with the fewest hydrogens”


Why ???

The stability of Carbocation

(1) Hyperconjugation & (2) Induction


Mechanism of Electrophilic Addition to Alkenes

The Point is which carbocation is more stable !!


Hyperconjugation: Alkyl group stabilize carbocation


The transmission of charge through a chain of atoms in a molecule by electrostatic induction

types of addition rxns
Types of Addition Rxns
  • Addition of Halogens
  • Addition of Water (hydration)
  • Addition of Acids
  • Addition of a hydrogen-boron bond to an alkene
  • The Point is that ‘hydrogen’ is more electronegative than ‘boron’
quick reminder
Quick Reminder
  • Alkene Reaction goes through the pathway of the most stable intermediate
  • The more substituents on an electron deficient carbon (carbocation or radical), the greater its stability
additions to conjugated systems
Additions to Conjugated Systems



How to Predict ?

Electrophile adds to alkene according to Markovnikov’s rule

Draw possible resonance structures and see how many structures come out

Selectivity may differ depending on the stability of each resonance structure

cycloaddition to conjugated dienes the diels alder reaction
Cycloaddition to Conjugated Dienes- The Diels-Alder Reaction -


  • Concerted as with hydroboration
  • Easy to synthesize a cyclic compound
  • Converts three pi bonds to two sigma bonds & one new pi bond
  • HOMO of diene and LUMO of dienophile
free radical additions
Free-Radical Additions

Initiation by a radical initiator: A radical is created from a non-radical precursor

Chain propagation: A radical reacts with a non-radical to produce a new radical species

Chain termination: Two radicals react with each other to create a non-radical species

Chain branching: see page 102 middle


other reactions with alkenes
Other reactions with alkenes
  • Ozonolysis
    • The oxidation of alkenes with ozone to give carbonyl compounds
    • One can deduce the structure of an unknown alkene