Abstract The 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 [BOND] O [BOND] C [DOUBLE BOND] C [BOND] O [BOND] moiety found in the exocyclic isomers, ie the stabilizing effect of a MeO group on the olefinic linkage of 2-methylenetetrahydrofuran. All three isomeric ...