Conformational and Structural Investigation of Substituted Hydrocarbons and Ring Compounds by Vibrational and Microwave Spectroscopy
Abstract
The physiochemical properties of a molecule of interest are usually obtained from
its molecular structure, and it involves the orientation of one part of the molecule about a
particular bond with respect to the rest of the molecule. These properties depend mainly
upon the three-dimensional arrangement of one part of the molecule in space with respect
to the other and, additionally, the way the molecule will react chemically and its available
reaction pathways are often critically dependent upon the orientation of the reactant
molecule. The energy differences of various conformations generally strongly couple or
interact by way of nonbonded interactions which even though are individually too weak
to determine, any single geometric feature may nevertheless act together to uniquely
determine the spatial structures of large and complicated molecules such as proteins and
DNA. Therefore, conformational analysis can lead to significant improvement in the
understanding of more complex system.
The infrared (3100-40 cm⁻¹) and Raman spectra (3200-20 cm⁻¹) of a number of
substituted (thiol, isocyanide, cyanide, acetylchloride, silane, amine, and phosphine) ring
and straight chain molecules were recorded in the gaseous, liquid and solid phases.
Additionally, variable temperature studies of the infrared spectra of the sample dissolved
in xenon has been carried out. From these spectral data, the possible stable conformers
have been identified and the enthalpy differences are given among the various forms for
each molecule. By utilizing microwave determined rotational constants for the
isotopomer(s) combined with the structural parameters predicted from the MP2(full)/6
311+G(d,p) calculations, adjusted r0 structural parameters have been obtained for the
stable forms of some molecules. Complete vibrational assignments are proposed for the
stable conformers of each molecule. To support the vibrational assignments, normal
coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations
were carried out to predict the fundamental vibrational frequencies, infrared intensities,
Raman activities, depolarization values and infrared band contours. The results will be
discussed and compared to the corresponding properties of some analogous molecules
wherever possible.
Table of Contents
Introduction-- Experimental and theoretical methods -- Microwave, infrared, and raman spectra, r0 structural parameters, conformational, stability, and vibrational assignment of allyl thiol -- Raman and infrared spectra, r0 structural parameters and vibrational assignments of (CH3)2PX where X=H, CH, and C1 -- Structure and conformation studies from temperature dependent infrared spectra of xenon cyclobutylgermane -- Conformational and structural studies of ethnylcyclopentane from temperature dependent raman spectra of xenon solutions and ab initio calculations -- Microwave, structural, conformational, vibrational studies and ab initio calculations of isocyanocyclopentane -- Microwave, infrared, and raman spectra, structural parameters, vibrational assignments and theoretical calculations of 1,1,3.3-tetrafluoro-3,3-disilacyclopentane -- Microwave, infrared, and raman spectra, structural parameters, vibrational assignments and theoretical calculations of 1,3-disilacyclopentane -- Microwave and infrared spectra, adjusted r0 structural parameters, conformational stabilities, vibrational assignments and theoretical calculations of cyclobutylcarboxylic acid chloride -- Microwave, r0 structural parameters conformational stability and vibrational assignment of cyclopropylcyanosilane -- Microwave, structural, conformational, vibrational studies and ab initio calculations of fluoroacetyl chloride
Degree
Ph.D.