Infrared spectroscopy has been used to determine thermodynamic parameters for the reaction between ethanol and acetone in CC14 and in the vapour phase in which a hydrogen-bonded complex is formed. In carbon tetrachloride, AHf^ = -15.3 kJ mol"1 and ASf"0" = -50.8 J mol"1 K" 1 . These values are consistent with data reported in the literature for related alcohols. Equilibrium constants for the vapour phase reaction were not reproducible, possibly due to a combination of adsorption and pressure effects.The IR spectra of propionic and acetic acids was studied indilute CCl^ and for acetic acid (at low acid pressure) in gaseous argon mixtures. Bands were assigned to the monomer and dimer. Spectra confirm that carboxylic acids are much more strongly hydrogen-bonded than the corresponding alcohols. The IR spectra of acetic, propionic, butyric, benzoic, omethoxyland o-ethoxy benzoic, p-methoxyl and p-ethoxybenzoic and o-acetyl salicylic acids was studied in CCl^.The effect of inter and intramolecular hydrogen-bonding is discussed. Models of monomer and dimer carboxylic acids were constructed using the Chem-X computer modelling package(Chemical Design Ltd.). Molecular energies were generated for the most stable acid conformations. For o-methoxybenzoic acid, the variation of molecular energy with the degree of internal rotation for the four bonds for which internal rotation was feasible was plotted using Chem-X.The J-CAMP.DX file protocol was used to import IR spectra into the Chem-X package. The future potential of combining modelling and spectroscopic packages is discussed.
|Date of Award
|Rhobert Lewis (Supervisor)