Abstract
Rotational isomeric state models of sulphur and selenium chains are used in a calculation of the entropy changes in the formation of cyclooctasulphur and cyclooctaselenium in the liquid state. Rings are assumed to be formed from linear polymers by the production and cyclization of octa-atomic diradicals. The probability that termini of catenaoctasulphur and catenaoctaselenium are in close proximity for bond formation is calculated by the computation of end-to-end distances in different chain conformations, and not by the assumption of Gaussian statistics.