The 13C NMR spectra of poly(1-pentenylene) and poly(1,3-cyclopentylenevinylene)

¹³C NMR spectra were obtained for polymers made by ring-opening polymerization of cyclopentene and bicyclo[2.2.1]hept-2-ene respectively. The fraction of cis double bonds could be determined with much greater precision from ¹³C NMR spectra than from IR spectra and varied from 0,66 to 0,31 for the samples of poly(1-pentenylene), ( 2 ), and from 1,0 to 0,14 for the samples of poly(1,3-cyclopentylenevinylene), ( 4 ). This is the first time an all-cis polymer of 4 has been reported. The spectra of 2 showed a cis (upfield) and trans (downfield) peak for each of ?CH and α-CH₂, but only one peak for β-CH₂. The spectra of 4 showed multiple fine structure, the main splittings corresponding to a cis (upfield) and trans (downfield) peak for α-CH, and a reverse line order for the other three carbons; subsidiary splittings were observed for all but the olefinic carbons, interpreted in terms of sensitivity of the chemical shifts to the cis/trans structure at the next nearest double bond. A complete interpretation of the line orders in 4 is given in terms of steric compression effects. The possibility that ring tacticity accounts for some of the fine structure cannot be entirely discounted. The stereochemistry of 4 is discussed in relation to the four possible modes of addition of monomer to a carbene chain carrier during polymerization.