Skip to content

Alkenes

Electrophilic Addition

The main mechanism of Alkenes is electrophilic addition.

\[ \begin{align*} \ce{\phantom{R_1R_2\bond{~-}CHR_3 + E\bond{~}Nu -> R1R2}+\phantom{ - CHR3E + Nu-}} \\ \ce{R_1R_2C\bond{~-}CHR_3 + E\bond{~}Nu -> R1R2C - CHR3E + Nu-} \\ \ce{\phantom{R1R2}+\phantom{HR3E + Nu- -> R1R2NuC - CHR3E}} \\ \ce{R1R2C - CHR3E + Nu- -> R1R2NuC - CHR3E} \end{align*} \]

Markovnikov's Rule

"The rich become richer"

In essence, Markovnikov's Rule deals with the fact that in the second stage of electrophilic addition, the nucleophile is likely to attack the more highly substituted carbon.

Every Single Reaction

Hydrogenation

\[ \ce{MeHC = CH2 + H-H ->[\text{Ni/Pd/Pt/Rh}][heat] MeH_2C - CH_3} \]

Halogenation

Mono-Halogenation

\[\ce{MeHC = CH2 + H-X -> MeHXC - CH3}\]

Di-Halogenation

\[\ce{MeHC = CH2 + X-X ->[CH3Cl\text{(org solvent)}][dark] MeHXC - CH2X}\]

Halohydration

\[\ce{ MeHC = CH2 + X-X ->[H2O\text{ (aq solvent)}][dark] Me(OH)HC - CH2X}\]

Hydration

\[\ce{ MeHC = CH2 + H-OH ->[\text{1) Cold conc. }H2SO4][2) warm H2O] Me(OH)HC - CH3}\]

Oxidation

Dihydration

\[\ce{ MeHC = CH2 ->[\text{Cold }KMNO4][dark] Me(OH)HC - CH2OH}\]

Ozonolysis

\[\ce{ Me2C = CHMe ->[1) O3][2) Zn, H2O] Me2C=O + O=CHMe}\]

Complete Oxidation

\[ \begin{aligned} \ce{ Me2C = CHMe & ->[Hot KMNO4/H+] Me2C=O + O=C(OH)Me} \\ \ce{ MeHC = CH2 & ->[Hot KMNO4/H+] Me(OH)C=O + CO2 + H2O} \\ \end{aligned} \]

Preparation of Alkenes

Dehydration

\[\ce{R1R2HC - C(OH)R3R4 ->[\text{conc. }H2SO4 or hot Al2O3 (s)][heat] R1R2C = CR3R4 + H2O}\]

Dehalogenation

\[ \ce{R1R2HC - C(X)R3R4 ->[\text{alc. }KOH][heat] R1R2C = CR3R4 + HX} \]

Zaitsev's Rule

  • trans configuration better than cis configuration (Geometric Isomerism)
  • More Highly Substituted Alkene is more stable