Macrocyclic phospholipids containing 32-44 ring atoms were synthesized by a route involving a high-temperature Glaser oxidation as the key step. There lipids are analogous to mammalian phospholipids except a single extra carbon-carbon bond joins the chain termini. The new lipids offered, therefore, an opportunity to examine thermotropic properties of their membranes when the chains within a given molecule are unable to move independently of one another. It was concluded that chain «tetherings» (a) raiser the transition temperatures substantially for all but the shortest lipids, (b) lowers enthalpies of transition by, in part, reducing the number of gauche C-C linkages created during the melting process, and (c) lowers entropies oftransition by impeding motional freedom within the liquid-crystalline phase