Relative thermodynamic stabilities of isomeric alkyl allyl and alkyl (Z)-propenyl ethers |
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Authors: | Esko Taskinen |
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Institution: | Department of Chemistry, University of Turku, FIN-20500 Turku, Finland |
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Abstract: | 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 ΔGΘ, ΔHΘ and ΔSΘ of isomerization at 298.15 K were evaluated. The propenyl ethers are highly favored at equilibrium, the values of both ΔGΘ and ΔHΘ 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 methoxy-substituted alkyl groups. In most cases the entropy contribution is negligible; however, for R = (MeO)2CH and R = (MeO)3C the values of ΔSΘ are ca. ?5 J K?1 mol?1. |
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