Can anyone refer me to papers discussing the small barrier motions in small ring systems that Bill Gwinn and coworkers described as "pseudorotation" about 35 years ago? What I am looking for is methods of calculating contributions to thermodynamic properties (energy, entropy) from such motions. REH Robert E. Harris Phone: 573-882-3274 Fax: 573-882-2754 Department of Chemistry, University of Missouri-Columbia Columbia, Missouri, USA 65211