Depolarized Rayleigh Scattering Research Articles

Etude structurale de composes organosilicies par diffusion Rayleigh depolarisee : I. Etude critique du signe des anisotropies optiques de liaisons et de groupes silicies ou non

The molecular optical anisotropies, γ 2, of ethylenic compounds with Ct-Bu groups, of alkyl- and alkenyl-silanes with CSiR 3 groups (R = Me, Et, Pr), amines and silylamines with NR′ groups (R′ = Me, t-Bu, i-Pr) and NSiR 3 groups, ethers, alkoxysilanes and disiloxanes with OMe, Ot-Bu and OSiR 3 groups, have been determined both in cyclohexane solution and in the pure liquid state by means of depolarized Rayleigh scattering (DRS). In order to interpret the results, a convenient criterium for determining the sign of the optical anisotropies of bonds and ZMR 3 groups with ∞-fold symmetry is proposed. The criterium, based on the positive character of the principal optical polarisabilities of bonds, only requires the knowledge of the mean polarisabilities of bonds, which are determined with 546 nm wavelength.

Solvent effects on some optical and spectroscopic properties of aromatic compounds

In this work we want of report some solvent effects observed during studies on benzenoid and heterocylic compounds by the Faraday effect and Depolarized Rayleigh Scattering (DRS), and their TCNE-complexes, by UV-visible spectrophotometry. The measured properties, respectively molecular magnetooptical rotation ([ϱ] M), molecular optical anisotropy (γ 2) and maximum absorption wavenumber ( − v max) undergo rather large changes when moving the gas phase to pure liquid or dissolved state, and vary weakly from a solvent to another one. As regards weak interactions, the Faraday effect allows essentially to observed internal field changes (Lorentz correction). It is likely that this bulk effect is not restricted to ‘aromatic’ solute. Moreover most solutesolvent interactions are masked by this non-specific medium effect, since even with polar solvents (CHCl 3, alcohols) no specific interaction given by π-donors and/or polar solute ( e.g. halobenzenes, anisole, …) is detected. So, for a given substance, the true value of [ϱ] M is obtained in the pure liquid state or in solvent as refractive as the solute. On the contrary, DRS, very sensitive to oriented interactions, can detect diatropism or paratropism in liquids. Therefore, to get comparable, ‘intrinsic’ γ 2 values one must now work with pure liquids but rather with dilute solutions in the same ‘inert’ solvent, that is a non-polar, weakly anisotropic one, containing bonds of the same kind as the solute. Accordingly, for organic compounds (H bonds), cyclohexane is preferred to CCl 4 (which may also give specific interactions). On the other hand the molar volume of the solvent need not be taken into account. The cases of benzene and some heterocyclics illustrate these principles. Finally, spectrophotometric studies of molecular complexes show that the influence of non-polar solvents on − v max generally reduces to a gross medium effect involving a linear function of (n 2 - 1)(2n 2 + 1). As regards polar solvents, more complex interactions with aromatic compounds and acceptor are likely to occur, and no correlation can be found with polarity parameters like Z or E T. TCNE-complexes of benzene, benzothiophene (after deconvolution of spectra) and dibenzothiophene are considered.

ChemInform Abstract: DEPOLARIZED RAYLEIGH SCATTERING STUDY OF PYRIDINE IN CYCLOHEXANE

Chemischer InformationsdienstVolume 10, Issue 28 Physical Organic Chemistry ChemInform Abstract: DEPOLARIZED RAYLEIGH SCATTERING STUDY OF PYRIDINE IN CYCLOHEXANE S. L. WHITTENBURG, S. L. WHITTENBURGSearch for more papers by this authorD. R. JONES, D. R. JONESSearch for more papers by this authorD. H. CHRISTENSEN, D. H. CHRISTENSENSearch for more papers by this authorC. H. WANG, C. H. WANGSearch for more papers by this author S. L. WHITTENBURG, S. L. WHITTENBURGSearch for more papers by this authorD. R. JONES, D. R. JONESSearch for more papers by this authorD. H. CHRISTENSEN, D. H. CHRISTENSENSearch for more papers by this authorC. H. WANG, C. H. WANGSearch for more papers by this author First published: July 10, 1979 https://doi.org/10.1002/chin.197928039AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, Issue28July 10, 1979 RelatedInformation

Introductory lecture: levels of order in amorphous polymers

Early theoretical predictions that amorphous and liquid polymers should be devoid of significant order down to dimensions commensurate with the diameter of the chain are supported by an extensive body of evidence from X-ray scattering at small and at wide angles, neutron scattering at small and at intermediate angles, recent electron microscopic investigations, analysis of rubber elasticity including, especially, its dependence on temperature and dilution, and cyclization equilibrium constants. If the nodular domains previously observed in electron micrographs are dismissed as artifacts, as studies documented in this Discussion indicate, then depolarized Rayleigh scattering (DRS) offers the only substantial evidence for a detectable degree of order in liquids consisting of long-chain molecules. This evidence is examined in detail. The analysis presented leads to the conclusion that the enhancement of the DRS of higher n-alkanes by factors of 2–2.5 over the values that would be observed for uncorrelated molecules is attributable to: (i) steric constraints on relative orientations of neighbouring chains which restrict them to orientations generated by rotation about one axis only, this axis being normal to their plane of contact, and (ii) a small preference in the alignment of neighbouring chains. These correlations do not imply order in the sense in which this term customarily is used. Rather, they complement the distance correlations manifested in the radial distribution functions deduced from wide-angle X-ray scattering; like them, they are of very short range.

Depolarized Rayleigh Scattering: Reorientational Motion and Orientational Correlations in Acetonitrile and Carbon Disulfide

AbstractDepolarized Rayleigh scattering experiments on neat acetonitrile and carbon disulfide as well as on mixtures of these liquids with carbon tetrachloride are reported. The collective reorientational correlation time τLS has been determined which is then compared with the single particle correlation time τS. From the comparison information on an orientational structure factor g(2), which is closely related to the Kirkwood g‐factor of polar fluids, can be obtained. Combination of g(2) and Kirkwood g‐factor results shows that a preferred antiparallel alignment is the most probable orientational structure in acetonitrile. For CS2 a Kirkwood g‐factor cannot be defined due to symmetry. Here the experiments indicate a preferred parallel arrangement of neighbouring molecules.

Virtual Nematic-Isotropic Transitions

Abstract A new method for the determination of virtual nematic isotropic transitions is given. The method is based on the measurement of angular correlations in the isotropic phase by means of Depolarized Rayleigh Scattering. It provides a good tool for the study of the nematogenic power of substituents and to estimate the effect of disubstitutions on any central rigid core.

Conformational Analysis of Stereoisomers of Triphenylheptane by Depolarized Rayleigh Scattering

Conformational Analysis of Stereoisomers of Triphenylheptane by Depolarized Rayleigh Scattering

Optical anisotropy of polystyrene and its low molecular analogues

Depolarized Rayleigh scattering (DRS) of benzene, toluene, cumene, and t-butylbenzene, 2,4-diphenylpentane (DPP) 2,4,6-triphenylheptane (TPH), and atactic polystyrenes (PS) with average degrees of polymerization of 21, 38 and 96 have been measured in carbon tetrachloride at λ= 632.8 nm and T= 25°C. The optical anisotropies γ2 deduced from the DRS of benzene and toluene are consistent with results obtained by LeFevre and co-workers from the electric and magnetic birefringence. The anisotropy attributable to the phenyl group is altered markedly by methyl substitution in passing from benzene to toluene. Further substitution on the methyl group has only a minor effect. Optical anisotropies of PS and its oligomers DPP and TPH are calculated from the polarizability tensor for cumene, chosen as the closest analogue of the repeating unit of PS. Values of 〈γ2〉 computed on this basis by averaging over the conformations of meso and racemic DPP, of the mixture of isomers comprising TPH, and of atactic PS are in good agreement with the results of the DRS measurements. 〈γ2〉 for PS calculated as a function of stereochemical constitution decreases from 97 A6 to 30 A6 in passing from syndiotactic to isotactic chains.

Separation of collision-induced from intrinsic molecular depolarized Rayleigh scattering optical anisotropy of the C—Cl bond

A procedure is demonstrated for separating the intrinsic molecular component of the depolarized Rayleigh scattering (DRS) from the transient, collision-induced contribution. It depends on the use of two interference filters of differing breadths (18 and 53 cm–1, respectively) to distinguish the narrow reorientational component of <3 cm–1 half-width from the much broader collisional scattering. The procedure is applied to CCl4 and four other spherically symmetric molecules in the liquid state. All exhibit small residual scattering (Rayleigh ratios RHV≈ 0.01–0.02 × 10–6 cm–1) at low frequencies ω from the central line, in addition to copious induced scattering over a broader range of ω. Approximately half of the scattering by neat liquid CHCl3, (CH3)2CHCl, (CH3)3CCl and CH3CCl3 is collision induced. Measurements on CCl4 solutions of each of these anisotropic molecules, corrected for collisional scattering and extrapolated to infinite dilution, yield molecular anisotropies γ2= 2.6, 1.6, 2.2 and 2.1 A6, respectively. These results give ΓCCl=ΔαCCl–ΔαCH= 1.6, 1.5, 2.0, 2.0 A3, respectively, where ΔαCCl and ΔαCH are the indicated bond anisotropies. They are in good agreement with values obtained from electric birefringence and absolute Raman intensities. Discordant values of γ2, and hence of ΓCCl, found by Bothorel and co-workers are in error due to their failure to eliminate collisional scattering. Conformational averages 〈γ2〉 for ClCH2CH2Cl and for meso and racemic CH3CHClCH2CHClCH3 calculated by rotational isomeric analysis using ΓCCl= 1.5 A3, as found for (CH3)2CHCl, are in good agreement with values measured in CCl4, viz., 5.5, 2.2 and 0.5 A6, respectively.

Conformations et stereoregularite de poly 2 vinyl pyridines—I Etude experimentale

Study of the average molecular optical anisotropy 〈 γ 2〉 of atactic and isotactic poly 2 vinyl pyridines of low polydispersity has been carried out in various solvents by means of depolarized Rayleigh scattering (D.R.S.) Experimental evidence (D.R.S. and viscosity) for free charges both on atactic and isotactic chains has been found in methanol and dimethyl formamide; their effect on 〈 γ 2〉 has been analyzed. The influence on molecular optical anisotropy of thermodynamic quality of the solvent has also been studied. Finally, comparison of the experimental optical anisotropies of atactic and isotactic structures reveals the strong effect of stereoregularity on the physical property under study.

ChemInform Abstract: DEPOLARIZED RAYLEIGH SCATTERING AND ORIENTATIONAL RELAXATION OF MOLECULES IN SOLUTION PART 1, BENZENE, TOLUENE, AND PARA‐XYLENE

Chemischer InformationsdienstVolume 4, Issue 36 Physical Organic Chemistry ChemInform Abstract: DEPOLARIZED RAYLEIGH SCATTERING AND ORIENTATIONAL RELAXATION OF MOLECULES IN SOLUTION PART 1, BENZENE, TOLUENE, AND PARA-XYLENE G. R. ALMS, G. R. ALMSSearch for more papers by this authorD. R. BAUER, D. R. BAUERSearch for more papers by this authorJ. I. BRAUMAN, J. I. BRAUMANSearch for more papers by this authorR. PECORA, R. PECORASearch for more papers by this author G. R. ALMS, G. R. ALMSSearch for more papers by this authorD. R. BAUER, D. R. BAUERSearch for more papers by this authorJ. I. BRAUMAN, J. I. BRAUMANSearch for more papers by this authorR. PECORA, R. PECORASearch for more papers by this author First published: September 4, 1973 https://doi.org/10.1002/chin.197336079AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume4, Issue36September 4, 1973 RelatedInformation

Depolarized Rayleigh Scattering and Stereoregularity of Polystyrene Chains. II. Interpretation

The molecular optical anisotropy of isotactic and atactic polystyrene, and their oligomers has been interpreted according to the rotational isomeric state model. The results obtained allowed us to determine the statistical weights of meso- and racemic 2,4-diphenylpentane and the respective orientation of the phenyl rings in these molecules. Analysis also showed that isotactic polystyrene in solution had the same local conformation as the meso pentane. This conformation consisted of a succession of very long helical segments of type 31. In the case of atactic polystyrene a conformation of identical nature was found, though the length of isotactic sequences was much smaller.Finally, this study shows that it has been possible to interpret, by means of conformational parameters of model compounds, all the experimental values observed for isotactic and atactic polymers, thus pointing out the utility of depolarized Rayleigh Scattering as a method for the determination of the average conformation of polymers as well as that of short chains.

Depolarized Rayleigh Scattering and Stereoregularity of Polystyrene Chains. I. Experimental

The study of the average molecular optical anisotropy ‹γ2› of atactic and isotactic polystyrene chains together with their oligomers has been carried out by means of depolarized Rayleigh scattering.In the case of atactic compounds a systematic study of molecular optical anisotropy has also been made as a function of the degree of polymerization, polydispersity, and solvent.The comparison of the experimental optical anisotropies of atactic and isotactic structures reveals a considerable difference, approximately 10 fold, thus pointing out the specific importance of the structural information that we can hope to obtain from the optical anisotropy.

Dispersion of the molecular optical anisotropy by Depolarized Rayleigh Scattering and birefringence induced by high energy laser waves

The wavelength dependence of the molecular optical anisotropy is discussed from quantum theoretical treatment and semiempiric formulations. Depolaiized Rayleigh Scattering (DRS) and birefringence induced by laser waves (BI), two optical effects giving direct information about optical anisotropy, have been investigated by the use of laser waves and their harmonics. CW gas laser (1–80 MW), as well as powerful Qswitched waves (1–30 MW) have been used. Results are reported in the wavelength range: 347.1 nm (second harmonic of the Cr 3+/ruby laser)−1060 nm first harmonic of the Nd 3+/glass laser). DRS and BI results show very little dispersion of the optical anisotropy of n-alkanes, in good agreement with their far-uv absorption spectra, but a larger one for carbon disulfide and aromatic compounds such as benzene and pyridine.

Agreement between Depolarized Rayleigh Scattering and Optical Kerr Effect Induced byQ-Switched Laser Waves in Some Liquids

We report measurements of the optical Kerr effect induced by $Q$-switched laser waves in some liquids, using an original experimental arrangement allowing easy measurements in weak anisotropic liquids. We compared the results obtained by this method to those deduced from our direct measurements of depolarized Rayleigh scattering. It is the first time that a good agreement has been found between these two effects, allowing precise determinations of apparent optical anisotropies.

The viscomagnetic effect in N 2, CO 2, CO, CH 4 and CF 4

Results are reported on the change of the viscosity of N 2, CO 2, CO, CH 4 and CF 4 under the influence of a magnetic field. The experiments were performed in a capillary Wheatstone bridge and with two orientations of the field with respect to the flow direction. The experimental data are compared with the results of a Chapman-Enskog treatment of the field effect for viscosity. It is shown that a term [ J] (2), which is connected to inelastic collisions ( Δm J ≠ 0 and/ or ΔJ ≠ 0), dominates the effect. The reorientation cross section for angular momentum has been calculated. The results are in excellent agreement with those obtained from Nuclear Magnetic Resonance and Depolarized Rayleigh Scattering experiments.