Stereochemical equilibration of 2,4,6-trichloro-n-heptane (TCH) in dimethyl sulphoxide at 70°C in the presence of LiCl yields a mixture containing 11.1 ± 0.2 % of the isotactic isomer and 42.7 ± 0.2 % of the syndiotactic isomer. These results, in conjunction with the ratio 0.362/0.638 for the meso and racemic 2,4-dichloro-n-pentanes (DCP) at equilibrium at 70°C are interpreted according to the theory of stereochemical equilibrium.

The statistical weight parameters thus evaluated are used for theoretical calculation of the proportions of various conformers in the three diastereoisomers of TCH. These calculations are compared with estimates of Doskočilová and coworkers from n.m.r. coupling constants. It is confirmed that the less-favoured conformations contribute appreciably to the conformer populations in the isomers of TCH, owing to the small size of the chlorine substituent. Stereochemical equilibria and conformer populations calculated for poly(vinyl chloride)(PVC) from the same parameters show significant departures from those of the oligomers. The calculated average length of sequences of the preferred conformation (tgtg, etc.) for isotactic PVC is much smaller than for an isotactic vinyl polymer having a larger substituent.