AbstractThe relative thermodynamic stabilities of the title compounds were determined by iodine catalyzed chemical equilibration in cyclohexane solution. The main point of interest was a determination of the thermodynamic stability of the OCCO moiety found in the exocyclic isomers, i.e. the stabilizing effect of a MeO group on the olefinic linkage of 2‐methylenetetrahydrofuran. All three isomeric compounds have essentially similar enthalpy values, which, in comparison with some previous thermodynamic data, shows that the double bond stabilization energy of the MeO group in the exo isomers is onlyca3 kJ mol−1. The entropy difference between the geometrical isomers is negligible, whereas the endo isomer is favoured by an entropy contribution ofc