The Carbon-13 NMR Spectra of Alkyl Vinyl Ethers, and Their Structures and Reactivities

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The <SUP>13</SUP>C NMR spectra of alkyl vinyl ethers were investigated at 22.5°C with neat liquid at 15.09 MHz. When the alkyl group of the ether becomes more electron-donating, the chemical shift of the α-carbon of the vinyl group shifts to a higher field, and that of the β-carbon, to a lower field. From these results, it was concluded that the contribution of the resonance form, \barCH<SUB>2</SUB>–CH=\overset+O–R, in the ether decreases in the order of the increasing electron-repelling power of the alkyl group. Good correlations were obtained between the chemical shifts of the vinyl group and the reactivity of vinyl ether in the cationic reaction. When the ether becomes more reactive, the chemical shift of the α-carbon shifts to a higher field, and that of the β-carbon to a lower field. This fact clearly shows that the attack of the proton on the β-carbon is not the rate determining step in the cationic reaction of the vinyl group. Linear relations were obtained between the chemical shifts of β-methylene protons and of β-carbon, but no correlation was obtained between the chemical shifts of the α-methine proton and of the α-carbon.