I know for a fact that cis alkenes are less stable than trans alkenes due to steric repulsions.
But what bugs me is the fact that why systems such as 2-methylprop-1-ene, where I believe steric repulsions are greater than that in cis-but-2-ene, are more stable than its cis and trans counterparts.
I saw this being given in the stability order of alkenes in Solomons and Frhyle. I looked up Morrison and Boyd and it said the same thing. Paula Bruice said otherwise stating trans to be more stable.
Which is the correct order, and why?
Paula Bruice
Solomons and Frhyle
For reference, free energies of formation:
$$ \begin{array}{c|c} \text{Compound} & \Delta G^{\circ}_{f}\text{ in kJ mol}^{-1} \\\hline \text{2-methylpropene} & 58.1 \\ E\text{-2-butene} & 63.0 \\ Z\text{-2-butene} & 65.9 \\\hline \end{array} $$