We have examined the following crown thioethers by differential scanning calorimetry from −90 °C, or lower, up to their melting points:  1,4,7-trithiacyclononane (9S3); 1,5,9-trithiacyclododecane (12S3); 1,4,7,10-tetrathiacyclododecane (12S4); 1,4,8,11-tetrathiacyclotetradecane (14S4); 1,4,7,10,13-pentathiacyclopentadecane (15S5); and 1,5,9,13-tetrathiacyclohexadecane (16S4). We have identified new solid−solid phase transitions above room temperature in 12S3, in the α-phase of 14S4, in 15S5, and in both the α-phase and β-phase of 16S4. Of those crown thioethers examined, only 9S3 and 12S4 do not show any solid−solid phase transitions. From an analysis of the entropy of fusion, we find that only the high-temperature solid phase of 16S4 is orientationally disordered. Analysis of the entropy changes associated with the solid−solid phase transitions and with fusion indicate that all except 12S4 have considerably more conformational freedom in the melt than in the room-temperature solid. Insight into these conformational changes is of considerable importance for understanding complexation of thioethers to metals.

Photochemistry in confined environments can lead to both different products and different product distributions from those observed in solution photochemistry, leaving open questions concerning the chemical involvement of the host lattice, including whether it maintains its structure. We have found that photolysis of the urea inclusion compound of 5-nonanone shows destruction of the hexagonal urea host lattice and concomitant conversion to the close-packed tetragonal urea structure. In addition, irradiation of urea-d 4/5-nonanone gives substantial deuterium incorporation, especially at the α-CH3 of the fragmentation product, 2-hexanone. By studying both the rates of photochemical conversion of 5-nonanone and the loss of the urea host lattice in urea/5-nonanone, we deduce that the structural changes of the urea lattice are associated with fragmentation products that are too small (i.e., too volatile) to support urea inclusion compounds. Our observation of even more degradation of the urea host lattice upon photolysis of urea/2-hexanone, a reaction which leads to a greater proportion of smaller guests than for urea/5-nonanone, supports this conclusion.