AbstractThe vibrational spectra of a series of diesters of fumaric and maleic acids and also of substituted butadienes have been investigated over a range of temperatures and phases. The effects on infrared and Raman spectra of altering the temperature and phase of these compounds (using matrix isolation techniques in some cases) have been interpreted in terms of conformational equilibria; table (1) summarises the results.
Low frequency vibrations have been assigned as torsions associated with either C-CH3 or =C-C= bonds. The frequency of each torsion leads to a value for v3 or V*, functions relating to the barrier height opposing internal rotation, shown in table (2).
In a number of cases sharp bands in the infrared spectra of gaseous substituted butadienes were associated with a series of side bands. In order to assign bands of this nature in chloroprene the isoelectronic compound acryloyl chloride was studied. A comparative analysis indicated that these bands are hot bands due to perturbation of fundamental vibrations by torsional modes. From the intensities of these bands torsional frequencies have been estimated in some cases.
Vibrational assignments are proposed in all cases. From these assignments values for the gas phase thermodynamic functions are calculated for the substituted butadienes over a range of temperatures, using statistical mechanics. Thermodynamic functions are also presented for the following additional compounds over a range of temperatures:- crotonaldehyde, acrolein, acryloyl fluoride, glyoxal and oxalyl chloride.
These results enable a better understanding of vibrational spectra and provide quantitative data which characterises conformational equilibria in these compounds in terms of thermodynamic equilibria.
|Date of Award||1977|