Relative Thermodynamic Stabilities of Isomeric Alkyl Allyl and Alkyl (Z)-Propenyl Ethers

Article abstract of DOI:10.1016/S0040-4020(01)81820-2

The relative thermodynamic stabilities of ten allyl ethers (ROCH2CH=CH2) and the corresponding isomeric (Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst.From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔG<*>, ΔH<*> and ΔS<*> of isomerization at 298.15 K were evaluated.The propenyl ethers are highly favored at equilibrium, the values of both ΔG<*> and ΔH<*> for the allyl -> propenyl reaction being ca. -18 to 25 kJ mol^-1.The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxysubstituted alkyl groups.In most cases the entropy contribution is negligible; however, for R=(MeO)2CH and R=(MeO)3C the values of ΔS<*> are ca. -5 J K^-1 mol^1-.