Explain the Relative Stability of Alkenes – Hydrocarbons Notes

Relative Stability of Alkenes:

Various alkenes differ in stability. The extent of stability of alkenes depends upon following factors:

Position of double bond: 

1-Butene is less stable than 2-butene which is evident from their heats of combustions. 1-butene being least stable liberates more heat on combustion.

CH2 = CH – CH2 – CH3 + 6O2 → 4CO2 + 4 H2O                ∆H = -2719 kJ.mol-1


CH3 – CH = CH – CH3 + 6O2 → 4CO2 + 4 H2O                  ∆H = -2712 kJ.mol-1


The measurement and comparison of heat of combustion of different alkenes , give us a clue about the relative stability of these alkenes.

Number and nature of substituent:

More is the number of substituents on doubly bonded carbons more is the stability of alkenes. e.g. stability order in following is:

   CH3    CH3                      CH3

    │       │                            │

CH3 – C   =   C – CH3  >  CH3 – C   =   CH – CH3   >  CH3 – CH   =   CH – CH3 

If electronegative group is attached to double bonded carbon it decreases the stability, while alkyl groups increases the stability.

    CH3                                                                                    Cl

     │                                                                                       │

CH3 – C   =   CH – CH3  >  CH3 – CH   =   CH – CH3   > CH3 – C   =   CH – CH3 

Orientation of substituents on double bonded carbon:

Trans form is more stable than cis form.

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