Spectroscopic studies of small ring compounds in their ground and excited electronic states /
The vapor-phase far-infrared and Raman spectra of 2,3-dihydrothiophene and coumaran vapor have been recorded and analyzed. Ring-puckering energy levels and one- and two-dimensional potential energy functions were determined for the ring-twisting ground and excited states for 2,3-dihydrothiophene and...
| Main Author: | |
|---|---|
| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1999.
|
| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731681791&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The vapor-phase far-infrared and Raman spectra of 2,3-dihydrothiophene and coumaran vapor have been recorded and analyzed. Ring-puckering energy levels and one- and two-dimensional potential energy functions were determined for the ring-twisting ground and excited states for 2,3-dihydrothiophene and ring-flapping ground and excited states for coumaran. For 23-dihydrothiophene a two-dimensional calculation provides a barrier to planarity of 435 cm⁻¹ and a puckering dihedral angle of 31°. The magnitude of the interaction constant between the puckering and twisting vibrations was determined to be 1.67x10⁵ cm⁻¹/[], similar to values determined for related molecules. A one-dimensional calculation produced a barrier of 279 cm or coumaran, with energy minima corresponding to dihedral angles of []30°. The coumaran barrier is considerably higher than that for 2,3-dihydrofuran which does not have the attached benzene ring. The ring-puckering and ring-flapping vibrations of phthalan and 1,3-benzodioxole in their S₁([],[]*) electronic excited state have been studied using fluorescence excitation, dispersed, and ultraviolet absorption spectroscopies. For both molecules, type A absorption bonds result from A₁ --> A₁ and B₂ --> B₂ transitions to the S₁ vibronic levels. Ring-puckering levels for the S₁([],[]*) state were determined for the flapping ground and excited states. These were used to calculate both one- and two- dimensional potential energy surfaces that fit the observed spectra. In the S₁([],[]*) state phthalan was found to be planar and more rigid than in the ground state in terms of the puckering coordinate but less rigid along the flapping coordinate. 1,3-Benzodioxole, however, was found to be puckered with a dihedral angle of 22°. The barrier to planarity in the excited state is 264 cm⁻¹ compared to 164 cm⁻¹ in the ground state. This increase is ascribed to a reduced suppression of the anomeric effect by the benzene ring in the S₁([],[]*) state. The far-infrared spectrum of 2,5-dihydrofuran shows a dozen ring-puckering bands with overlapping rotational-vibrational bands in the 99 to 180 cm⁻¹ region. The rotational-vibrational bands show remarkable coincidences even though they originate from different puckering transitions. The band separations of 0.52 cm⁻¹ are consistent with the near-symmetric top structure of the molecule determined from its microwave spectra. |
|---|---|
| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xv, 153 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 149-152). |