Double bonds and their distribution

In the spectmm of poly( 1-butenylene), the a-carbons are sensitive to the configuration of the nearest double bond, but almost insensitive to that of the next nearest double bond, even though it is only three bonds away two opposing effects must cancel in this case. The olefinic carbons on the other hand are sensitive to the configuration of the next nearest double bond, which is four bonds away. When the polymer is made from cw,c/s-cycloocta-l,5-diene, every other double bond in the chain is preformed and must be cis. The spectrum of freshly formed polymer therefore shows only tc, cc, and ct olefinic peaks at 130.15, 129.63, and 129.46 

In the C NMR spectra of polymers of norbomene, all the ring carbons are sensitive to the configuration of the two nearest double bonds, while the olefinic carbons are sensitive to the three nearest double bonds, even though the third is five bonds away. The line positions are listed in Table 11.5. All these splittings disappear in the spectrum of the hydrogenated polymers so that none appear to be the result of m/r isomerism (Ivin 1977b Hamilton 1984a). 

The cis content in all these polymers can be readily determined from either their or H NMR spectra. The H NMR spectrum of polynorbomene gives well-resolved olefinic proton signals (multiplets) at 5.35 ppm (i) and 5.21 ppm (c), also a-proton signals (fine structure unresolved) at 2.8 ppm (c) and 2.45 ppm (r) (Larroche 1982). The C NMR spectra give, in addition, information on the proportions of double-bond dyads and triads, and hence on the distribution of cis and trans double bonds. There are two main questions to be answered (i) what 

This pattern of behaviour is found not only for the ROMP of norbomene (Ivin 1979c Greene 1986 Bencze 1996) but also for its derivatives, and for cyclopentene (Ceausescu 1986, 1988a). A very significant observation is that r, seldom falls below unity even when the cis content is high. This means that at high 

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