The formation of polymers has been observed on exposure of pure substituted benzenes to ultrasound intense enough to cause cavitation. The products have some of the characteristics of the char obtained from low temperature pyrolysis of hydrocarbons. They are difficult to dissolve, melt above 300 "C, and give a large broad e.p.r. signal. A crudecorrelation between bond dissociation energy and the reaction rate suggests that the initiation reaction is a thermal decomposition in a cavitation bubble. The phenomenon iscompared to radiolysis and thermal reactions.La formation de polymeres a etk observee lorsque des composes purs, du type benzenique substitues, sont exposes B des ultrasons suffisamment intenses pour provoquer des cavites. Les produits obtenus ont certaines des caracteristiques des produits de carbonisation provenant de la pyrolyse a basse temperature d'hydrocarbures. Ils sont difficiles B solubiliser, fondent au-dessus de 300 "C, et donnent en r.p.e. un signal tres large. Une correlation grossiere entre I'knergie de dissociation de liaison et la vitesse de reaction, suggere que la reaction d'initiation est une decomposition thermique dans unecafite en forme de bulle. Le phenomene est compare aux reactions thermiques et de radiolyse.

I3C NMR spectra of cis-cyclohexyl-15-crown-5 ether in the temperature range 298-173 K have been recorded. A single degenerate conformational process, attributed to cyclohexyl ring inversion, has been detected with a barrier of ca 10.3 kcal mol-'. Sodium ion complexation increases this barrier by ca 0.5 kcal mol-', whereas potassium ion complexation has no measurable effect. Spin-lattice relaxation time results also indicate more effective complexation of sodium ion than potassium ion by the macrocyclic crown ether system.