Enthalpies of formation of some cyclic 1,3- and 1,4-di- and poly-ethers: thermochemical strain in the –O–C–O– and –O–C–C–O– groups

Abstract

Enthalpies of combustion and vaporization at 298.15 K have been measured for five cyclic polyethers. Enthalpies of formation in the liquid and gaseous states have been derived: [graphic omitted]The results for cyclic 1,3- and 1,4-polyethers are discussed in terms of apparent strain energies relative to aliphatic polyethers. It is shown that there is a constant contribution to the apparent strain from each 1,3-dioxa and 1,4-dioxa unit, provided that the reference system consists of compounds which have conformations similar to those of the cyclic polyethers.