I. Study of Molecular Orbital Degeneracy in C₅H₅. II. The Crystal and Molecular Structure of Cyclopentadiene

Citation

Liebling, Gerald Richard (1965) I. Study of Molecular Orbital Degeneracy in C₅H₅. II. The Crystal and Molecular Structure of Cyclopentadiene. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KEZ8-7539. https://resolver.caltech.edu/CaltechETD:etd-09302002-122910

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Part I. The paramagnetic resonance of the cyclopentadienyl radical C5H5 has been observed in a single oriented crystal of cyclopentadiene at temperatures ranging from 25[degrees]K to 150[degrees]K. The spectra are of two types, high-temperature and low-temperature spectra, with the transition occurring reversibly between 70[degrees]K and 120[degrees]K. The high temperature spectra consist of six equally spaced lines with a splitting of 6.2 gauss and can be accounted for in terms of a uniform spin distribution around the ring and rapid reorientation of the ring in its plane. The low-temperature spectra are slightly anisotropic and can be reasonably well accounted for by a distorted C5H5 radical with a nonuniform spin distribution undergoing rapid reorientation in its molecular plane. Part II. The crystal structure of cyclopentadiene, C5H6, has been determined from X-ray diffraction photographs made at about -150[degrees]C. The crystals are monoclinic, space group P2[subscript 1]/n, with cell dimensions [...]. Intensities of 70 reflections recorded on four zero-level precession photographs were estimated visually and used in a least-squares refinement of the atomic coordinates. The final R factor for these reflections is 0.10. The five-membered ring of carbon atoms is planar; the values for the bond distances are in close agreement with those previously determined by electron diffraction techniques. ABSTRACTS OF PROPOSITIONS Proposition 1: A method of constructing semiconductor devices that would operate at very low temperatures is proposed. Proposition 2: It is proposed that the EPR spectra of x-irradiated trimesic acid be studied for the possibility of observing an aromatic sigma radical. Proposition 3: Several experiments are proposed that would elucidate the mechanism of carbene addition across a double bond. Proposition 4: It is proposed that attenuated total reflection spectroscopy can be very useful for studying electrode processes in electrochemical reactions. Proposition 5: Several EPR experiments are proposed.

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