C-13 NUCLEAR MAGNETIC-RESONANCE SPECTRA OF DIVINYL ETHERS

13C NMR chemical shifts have been determined for a number of alkyl- and aryl-substituted divinyl ethers. On the basis of the shift data for the olefinic carbons it can be shown that alkyl substitution at one of the terminal (β) carbons of the divinyl ether skeleton leads to an enhanced conjugation between the 0 atom and the unsubstituted vinyl group, whereas there is a decrease in conjugation with the substituted vinyl group. This is likely to arise from the polar effect of the substituent, which opposes the accumulation of excessive negative charge (resulting from conjugation) on the substituted C atom. Thus the O atom conjugates more effectively with the other vinyl group. The results suggest further that unsubstituted or β-(β,β'-) substituted divinyl ethers have an essentially planar s-trans,s-trans structure, while α-substituted divinyl ethers have a slightly nonplanar s-cis,s-trans structure, and α,α'-substituted divinyl ethers are markedly nonplanar so that π-p-π conjugation is considerably weaker in these compounds than in the unsubstituted divinyl ether molecule. © 1978, American Chemical Society. All rights reserved.