Master of Science (MS)
Semester of Degree Completion
Rebecca A. Peebles
The Fourier-transform microwave (FTMW) spectra of 1,2-dichloroethane (12DCE), 1-chloro-2-fluoroethane (1C2FE) and 2,3-dichloropropene (23DCP) have been studied in the 6 to 18 GHz range to determine experimental rotational constants, nuclear quadrupole coupling constants (NQCC) and quartic centrifugal distortions constants. These three molecules have different spatial arrangements (anti and gauche) resulting from different relative orientations of chlorine and/or fluorine atoms about the C-C single bond. The lowest energy anti conformer of 12DCE is non-polar and it is not detectable by microwave spectroscopy, but rotational spectra of gauche-12DCE with three isotopologues, gauche-1C2FE with three isotopologues, and both anti- and gauche-23DCP, each with two isotopologues, have been measured. 23DCP has been studied for the first time by FTMW spectroscopy, and some of the NQCC of all three molecules were also determined for the first time. Kraitchman’s equations were used to determine the rs coordinates of isotopically substituted atoms of 12DCE, 1C2FE and 23DCP, and the r0 structures were also deduced for 12DCE and 1C2FE from experimental rotational constants, and these structural parameters were compared with ab initio values (re) and previous results. The differences of structural parameters that were observed are small, but they are significant, and most differences can be explained by steric effects. The percent ionic character of the C-Cl bonds was calculated according to Townes-Dailey analysis and using Cl hyperfine coupling constants that were not available from previous studies and was found to be ~30% for all species studied. The experimental results have also proved that the level of ab initio calculations that was used has done good predictions of structures and microwave spectra, particularly for related species containing chlorine.
Dikkumbura, Asela Sampath, "Structures and Nuclear Quadrupole Coupling Tensors of 1,2-Dichloroethane, 1-Chloro-2-Fluoroethane and 2,3-Dichloropropene Studied Using Microwave Spectroscopy and Computational Chemistry" (2016). Masters Theses. 2443.