The Organic and Macromolecular Chemistry Program in the Chemistry Division at the National Science Foundation supports Professor John D. Roberts at the California Institute of Technology, who will capitalize on and extend an initial success with the strongly hydrogen-bonded monoanion of succinic acid for determining experimentally by NMR, the very important values of rotational dihedral angles of conformers of other 1, 2-disubstituted ethanes oriented in liquid-crystal or lyotropic solutions. A second objective is to contribute further to understanding the influences of solvents on the positions of equilibria between gauche and trans (anti) conformations, especially ones carrying polar, ionized and potentially hydrogen-bonded substituent groups that, besides being of substantial chemical interest and importance, are ubiquitous in molecules involved in living systems. This effort will be extended to compounds where electronic, hydrogen bonding and solvent effects are to be pitted against expected substantial steric effects, the latter commonly regarded as the primary cause of conformational preferences, even though much experience, shows that steric effects are essentially nonexistent or relatively minor in their influence on conformational preferences, unless the X and Y substituents are both tetrahedral groups, such as tert-butyl, trimethylammonium, sulfonic acid and the like. The research will provide an in-depth understanding of the conformational properties of disubstituted ethanes and experimental validation of the associated energetics. The dihedral angle versus energy relation in substituted ethanes is of direct relevance for developing improved understanding of both electrostatic and steric contributions to the free energy, impacting not only organic chemistry but also being relevant to far removed areas, such as understanding protein side chain structure and dynamics.
Broader impacts expected to result from the proposed activities are several, but especially through integrating research and teaching for the benefit of university undergraduates and motivated high-school students. Some are Caltech students, others come country-wide, or from abroad, more than half are women. A program is in place to expose them to a microcosm of the experience of a new young faculty member. It starts with writing a research proposal, then having it reviewed by a knowledgeable faculty group. With success there, planning on how to get the research work started; learning new techniques in synthesis or involving sophisticated instrumentation; writing up the results for publication; and presenting a oral report or poster at a public meeting in the style used by professional chemistry groups. Over a period of 20 years, 110 undergraduates have participated with 25 papers published and several others in essentially final draft form. The proposal lists the titles of nine articles with the names of undergraduates and high school students as co-authors and thirty project titles listing the students' names. These projects were carried out during 2003-2007.
