G. Michel

L'étude quantitative des complexes accepteur-donneur par spectrométrie Raman. La détermination de la constante de dissociation

Abstract The authors show that quantitative Raman spectrometry is a powerful method for studying acceptor—donor complexes. Preliminary experiments on ethyl acetate + AsCl3 mixtures support this fact. A general expression is given which can be used to obtain the “conditional” dissociation constant K(s) of a complex: this value is calculated from Raman line intensities measurements. The stoichiometry of the complex is obtained by J obs method. The authors were able to calculate the K(s) value of the systems C6H5COOC2H5 + SbCl3(I) and C6H5COCH3 + SbCl3(II) as solutions in ethyl ether and the K(s) value of the system (II) in CCl4.

Contribution à la spectrométrie Raman—II: Intensité de la raie du carbonyle aliphatique

Abstract The authors have investigated the Raman carbonyl stretching vibration of different aliphatic ketones, esters and aldehydes. The results concerning the frequency of the carbonyl are in agreement with those of previous workers; the mean values for an homologous series of saturated aliphatic ketones and esters are 1715 ± 3 cm −1 and 1738 ± 5 cm −1 . The scattering coefficient of the carbonyl line has been measured with an accuracy of 4 per cent and the following observations have been made: (1) The scattering coefficient of a non-conjugated carbonyl is relatively constant and proportional to the number of independent carbonyl groups in the molecule. (2) Conjugation of the carbonyl group with an ethylenic double bond increases strongly the scattering coefficient by a factor depending on the nature of the carbonyl (aldehyde,ketone or ester) the nature of the substituents on the molecule and the degree of conjugation allowed by steric factors

Un spectromètre Raman à grande résolution équipé d'une source conventionnelle et d'une source laser

Abstract A Raman sprectrometer of high resolving power, using conventional or laser source, has been described, and its use in measuring spectra of solid materials and for mixtures of isotopic species has been illustrated.

Contribution à la spectrometrie Raman—I: Construction d'un spectromètre enregistreur à grande dispersion

The authors describe the photoelectric recording Raman spectrometer which they have built; it consists of the following parts: (a) a light source of the Toronto-type helical mercury arc furnished by ARL. (b) a monoohromator, which is the result of the transformation of a three-prism Huet spectrograph (9 Amm), the scanning of the spectrum on a fixed exit slit, in front of the 1P21 photomultiplier tube is obtained by a plane mirror located between the camera lens and the focal plane. (c) a tuned amplifier giving the maximum positive reaction for the chopping frequency of light (about 31 cyclessec) and a Brown recorder. The authors discuss the choice of optical and electronic parameters to obtain the following performances: 1. reproducibility of intensity measurements of about 2%. 2. a signal/noise ratio of about 500 : 1 is obtained for the 992-cm−1 Raman line, with a time constant of 4 seconds. 3. the resolution is excellent; the two lines 992 cm−1 of benzene and 1001 cm−1 of cyclo-hexane, are fairly well separated.

Contribution à la spectrometrie Raman—VI. Intensité de la raie Rarnan carbonyle et facteurs électroniques

The Raman intensity-molecular structure correlation of the carbonyl group is discussed in terms of inductive, mesomeric and steric effects. This work is based on the scattering coefficients previously measured on a large number of esters, ketones, aldehydes and amides. The authors pointed out that the inductive effects have poor influence on the CO intensity of the Raman band. Attention is drawn to the influence of the conjugation on the Raman bands intensity, particularly in relation to the nature of the conjugated groups, their number and their mode of conjugation. They explain the existence of an exaltation sequence of the CO Raman band intensity in the following order amide < ester < ketone < aldehyde. The influence of the substitution in ethylenic and aromatic compounds is extensively discussed it is particularly clear that Raman intensities, in these cases, are very sensitive to the steric effects. In the para substituted aromatic compounds the scattering coefficient of the CO band appears to be chiefly dependent of the donor effect of the substituent.

Recherches sur l'analyse des mélanges liquides par spectrographie Raman

Abstract By technical improvements in the exact determination of the photographic plate contrast factors, the sensitonietric calibration and the densitometry, the following observations have been established : a) That for binary mixtures of non-associated compounds the theoretical proportionality between the intensity ratio of two lines and the molar ratio of the mixture has been confirmed over the range tested; deviations from this law observed by earlier workers have all been traced either to overlapping of lines or sensitometric errors. b) For binary mixtures of strongly associated liquids, the spectrum of the mixture is not always exactly the sum of the spectra of the components; new lines may appear. The proportionality relationship is conserved by the lines, due to vibrations within the molecule of groups not involved in the association, while other groups give strongly perturbed radiations. The study of these perturbations may throw useful light on the nature of association linkages in liquids. c) For ternary mixtures of alcohols, the influence of a third constituent on the intensity ratios of some of the lines of the first pair seems to be negligible. Since the line intensity ratios are proportional to the molar ratios, it should be possible to make use of relative diffusion coefficients for the analysis of more complex mixtures. Our work has improved the precision of the analytical determinations; the mean error does not exceed 0–8% and is often less than 0.5% for non-associated liquids; while for associated liquids the maximum error is only 3%.

Rotational vs vibrational relaxation in the ν(CO) bands of metal carbonyls

Abstract The i.r. and Raman spectra in the ν(CO) region of Cr(CO) 6 and Mn(CO) 5 Br are recorded in n -hexane, carbon tetrachloride, benzene and chloroform. The conclusions are (a) the half band widths are appreciably different, and show widely different sensitivity to solvent effects, even for modes involving the same carbonyl groups and (b) the half band widths are dominated by vibrational relaxation, contrary to common belief.

Description d'une cellule de 10 ml utilisable pour l'analyse quantitative avec un spectromètre Cary 81 équipé d'une lampe Toronto

Abstract A 10 ml cell for a Cary 81, in replacement of 65 ml cell is described. This former shows the same optical effect as the latter and is useful in quantitative analysis for smaller volumes.