Carbon-13 NMR study of the effect of the polar character of substituents on p-.pi. conjugation in .alpha.,.beta.-unsaturated ethers, acetals, orthoesters, and orthocarbonates
Carbon-13 NMR study of the effect of the polar character of substituents on p-.pi. conjugation in .alpha.,.beta.-unsaturated ethers, acetals, orthoesters, and orthocarbonates