M.A. Raso

A general fitting program for resolution of complex profiles

Abstract An interactive, conversational, general purpose program to fit experimental profiles to a set of distribution functions is reported. The non-convergence problem is discussed, and routines constituting a new procedure to solve it are explained and listed.

Vibrational spectra of ethyl acetate and monohaloacetates

Abstract Vibrational spectra of ethyl acetate and ethyl monohaloacetates have been studied. Infrared spectra in vapour and liquid phases, solutions in different solvents, and also Raman spectra of those compounds have been recorded in order to assign the fundamental bands. The existence of different rotamers about the CC bond joining the halomethyl and carbonyl groups produces a splitting in some bands of the spectra. It yields a more complex profile but, to some extent, it allows an easier assignment of those bands which present that splitting.

Vibrational spectra, normal vibrations and rotational isomerism of ethyl acetate and three deuterated analogues

Abstract IR and Raman spectra of ethyl acetates, CH3COOC2H5, CD3COOC2H5, CH3COOC2D5 and CD3COOC2D5, in the liquid and crystalline states have been recorded in the 3500-200 cm−1 region. These spectra are analysed on the basis of spectral comparison both among themselves and with spectra of the trichloro analogues CCl3COOC2H5 and CCl3COOC2D5 previously studied. All the ethyl acetates in the crystalline state give two completely separated carbonyl stretching Raman bands, suggesting that two, or an even number of molecules, exist in the crystal unit. Liquid-state spectra exhibit many band pairs arising from the trans-trans and trans-gauche conformers around CX3COOCX2CX3 axes (X = H and D) and the bands of the trans-trans conformer persist in the crystalline state. Normal coordinate calculations for the four species have been carried out on the two isomeric models using an MVIB program. The results explain wavenumber shifts on deuteration and the nature and separation of band pairs satisfactorily, and suggest that a large amount of vibrational coupling exists among skeletal stretching vibrations.

A general fitting program for resolution of complex profiles—II. Automatic baseline correction

Abstract An automatic baseline correction has been incorporated into a previously reported program for resolution of complex profiles. The interactive and conversational character of the program has been preserved. The algorithm developed to carry the correction through is reported and discussed, and further enhancements are suggested.

Vibrational spectra of ethyl dihaloacetates

Abstract Vibrational spectra of ethyl dihaloacetates have been studied. Infrared spectra in vapour and liquid phases, solutions in different solvents, and Raman spectra of these compounds have been recorded in order to assign the fundamental bands. The existence of different rotamers about the CC bonds joining the dihalomethyl and carbonyl groups produces a splitting in some bands of the spectra. It yields a more complex profile but, to some extent, it allows an easier assignment of bands which present that splitting. A theoretical study of the potential barrier hindering free rotation about that bond has been made in order to predetermine the number and orientation of the rotamers in each compound.

IR spectra of ethyl acetate and perfluorotertbutanol-ethyl acetate complex at different temperatures.

Abstract The infrared spectra of ethyl acetate in solid argon, at very low temperature, and in solution have been recorded. The bands assigned to the rotamers trans and gauche, originated from rotation around the OC 2 H 5 bond have been measured in these spectra. After annealing, the spectrum of the compound isolated in argon matrix approaches to the one observed in the crystal. From the IR spectra of a 1:1 solid mixture of ethyl acetate and perfluorotertbutanol at different temperatures (6K to 150K), identification of bands due to the complex vibrations was carried out. The relative intensity of bands attributed to the gauche rotamer was observed to increase in the mixture suggesting that this alcohol-ester association stabilises the gauche conformer of the ester.

Vibrational spectra and rotational isomerism of ethyl chloroacetate and three deuterated analogues

Abstract IR and Raman spectra of ethyl chloroacetate and three deuterated analogues, CH 2 ClCOOC 2 H 5 , CD 2 ClCOOC 2 H 5 , CH 2 ClCOOC 2 D 5 and CD 2 ClCOOC 2 D 5 , in the liquid and crystalline states have been recorded in the 3500-100 cm −1 region. These spectra are analysed on the basis of spectral comparison both among themselves and with spectra of related esters previously studied. Band pairs observed in the liquid-state spectra are classified into two groups, one appearing at positions similar to those for ethyl non-chloro- and trichloroacetates and the other at positions similar to those for the methyl chloroacetate. These groups of band pairs are interpreted as being associated with the trans and gauche conformations around the COCX 2 CX 3 axis (X  H or D), and the conformations around the ClCCO axis, respectively. The skeletal molecular conformation of ethyl chloroacetate in the crystalline state is suggested to be trans - trans around the ClCCOC 2 H 5 axes. Normal coordinate calculations for the four isotopic species have been carried out on the five isomeric models using an MVIB program. The results satisfactorily explain the observed wave-number shifts on deuteration and the nature and separation of the band pairs.

Conditions of measurement of infrared absorption band intensities by fourier transform spectrometry

Abstract The influence of infrared spectra of some different conditions required in the use of modern FTIR spectrometers has been studied. This work has been performed in two ways: firstly, the influence of factors such as apodization function, level of zero filling, number of data points and phase correction procedure is determined from experimental data, and, secondly, numerical simulation of the whole process has been carried out in order to separate experimental error from that deu to the mathematical treatment.

Thermodynamic functions of rotational equilibria in ethyl acetate and monohaloacetates

Abstract The integrated intensities of some paired bands of the infrared spectra of ethyl acetate, fluoroacetate and chloroacetate have been measured in cyclohexane solution at different temperatures. Values obtained have been used to calculate ΔHδ of the two rotational equilibria (generated by rotation of the halomethyl group around the CC bond and by rotation of the ethyl group around the OEt bond). Different methods have been used to calculate ΔSδ and the values obtained have been discussed. The components of the split bands were assigned to the expected conformers and used for statistical calculation of the entropy increment. This assignment has been verified using the sum rule of Mizushima and co-workers. Values obtained for ΔHδ and ΔSδ confirm the stability of the trans conformer of all three compounds when rotation of the ethyl group is considered. ΔHδ calculation for the equilibrium between trans and cis (or gauche) rotamers, defined by the rotation of the halomethyl group, predicts different behaviour for each of the two haloacetates studied, in agreement with experimental results.