Three-dimensional representation of metastable peaks at high mass resolution

Isobaric daughter ions formed from a common metastable ion have been analysed at high mass resolution. A three-dimensional representation is used to summarize the data for competitive CO and C₂H₄ losses and competitive CHO˙ and C₂H₅˙ losses from metastable molecular ions of cyclohexanone.     

Imidization reaction in polyvinylamides

Depending on their method of preparation, polyvinylamides can have nitrogen contents which vary from the theoretical value to considerably lower values. Cyanamer P-250, a polyacrylamide, manufactured by American Cyanamid Corporation, had a nitrogen content of 17.67% compared to the theoretical value of 19.7%. A polyacrylamide prepared in dioxane at 60°C and initiated by benzoyl peroxide, had a nitrogen content of only 15.5%. These low values are ascribed to loss of ammonia via intramolecular imide formation. We have found that when the intramolecular imidization reaction in poly acrylamide and in polymethacrylamide is driven to completion by heating the polymers in dilute solution, very close to 33% of the amide groups remain unreacted. Thus, unlike poly(methyl vinyl ketone) and poly(vinyl chloride), the poly-vinylamides do not obey Flory's statistical calculation for the random reaction of 1,3 groups in a head-to-tail polymer which predicts isolation of only 13.53% of the vinyl residues. Of the various possible explanations, the hypothesis of larger ring formation seems the most plausible, since specific interactions have been shown to exist between widely spaced amide groups in low molecular weight diamides. The infrared spectra of polyacrylimide and polymethacrylimide are presented and compared with those of the corresponding polyvinylamides. When the nitrogen content of polyacrylamide falls to the 14.9–15.4% N range due to imide formation, the polymer becomes water-insoluble. Because imidization stiffens the polymer chain and introduces weakly acidic groups, the imide content of a polyvinylamide should affect its compatibility with other polymeric systems.     

Rational design of molecular sheets composed of interconnecting eight- and twenty-four-membered rings: use of lithiated aggregates to control network assembly

The lithiated (organo)sulfonylacetonitrile complex [MeSO(2)CHCNLi.THF] (3) has been prepared and structurally characterized in order to demonstrate that well-known molecular aggregates of s-block metals may be used as building blocks in the controlled assembly of complex supramolecular architectures. The solid state structure of 3 can be described as a novel basket-weaved, 2-D network, composed of (SO(2)Li)(2) "dimeric" rings joined via "interdimer" donation of nitrile units.     

Modal stability of inclined cables subjected to vertical support excitation

In this paper the out-of-plane dynamic stability of inclined cables subjected to in-plane vertical support excitation is investigated. We compute stability boundaries for the out-of-plane modes using rescaling and averaging methods. Our study focuses on the 2:1 internal resonance phenomenon between modes that occurs when the excitation frequency is twice the first out-of-plane natural frequency of the cable. The second in-plane mode is excited directly, while the out-of-plane modes can be excited parametrically. An analytical model is developed in order to study the stability regions in parameter space. In this model we include nonlinear coupling effects with other modes, which have thus far been omitted from previous models of parametric excitation of inclined cables. Our study reflects the importance of such effects. Unstable parameter regions are defined for the selected cable configuration. The validity of the proposed stability model was tested experimentally using a small-scale cable actuator rig. A comparison between experimental and analytical results is presented in which very good agreement with model predictions was obtained.     

On optical depth profiling using confocal Raman spectroscopy

Until 2006 the performance of confocal Raman spectroscopy depth profiling was typically described and modeled through the application of geometrical optics, including refraction at the surface, to explain the degree of resolution and the precise form of the depth profile obtained from transparent and semicrystalline materials. Consequently a range of techniques, physical and analytical, was suggested to avoid the errors thus encountered in order to improve the practice of Raman spectroscopy, if not the understanding of the underlying mechanisms. These approaches were completely unsuccessful in accounting for the precise form of the depth profile, the fact that spectra obtained from laminated samples always contain characteristic peaks from all materials present both well above and below the focal point and that spectra can be obtained when focused some 40 μm above the sample surface. This paper provides further evidence that the physical processes underlying Raman spectroscopy are better modeled and explained through the concept of an extended illuminated volume contributing to the final Raman spectrum and modeled through a photon scattering approach rather than a point focus ray optics approach. The power of this numerical model lies in its ability to incorporate, simultaneously, the effects of degree of refraction at the surface (whether using a dry or oil objective lens), the degree of attenuation due to scatter by the bulk of the material, the Raman scattering efficiency of the material, and surface roughness effects. Through this we are now able to explain why even removing surface aberration and refraction effects through the use of oil immersion objective lenses cannot reliably ensure that the material sampled is only that at or close to the point of focus of the laser. Furthermore we show that the precise form of the depth profile is affected by the degree of flatness of the surface of the sample. Perhaps surprisingly, we show that the degree of flatness of the material surface is, in fact, more important than obtaining a precise refractive index match between the immersion oil and the material when seeking a high-quality depth profile or Raman spectrum from within a transparent or semicrystalline material, contrary to accepted norms that samples for interrogation by Raman spectroscopy require little preparation.     

Dynamics of light-induced reflectivity switching in gallium films deposited on silica by pulsed laser ablation

We present what is to our knowledge the first experimental study of light-induced reflectivity changes at an alpha-Ga/Si interface irradiated by femtosecond and picosecond laser pulses. After exposure, the reflectivity can increase from R?0.55 , which is typical for alpha-Ga , to R?0.8 , which is close to that of liquid Ga. The initial step in the reflectivity change of 2-4 ps is resolved with 150-fs laser pulses. The light-induced reflectivity change relaxes during 100ns-10 mus , depending strongly on the background temperature of the Ga mirror and the laser fluence.     

The microanalysis of fluorine-containing organic compounds

Summary Kirsten's method for the determination of nitrogen has been applied to the analysis of fluorine-containing organic compounds. Some slight modifications to the original method have been introduced.

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Zusammenfassung Die vonKirsten angegebene Methode zur Bestimmung von Stickstoff wurde für die Analyse fluorhältiger organischer Verbindungen angewendet. Einige geringfügige Modifikationen des ursprünglichen Verfahrens werden angegeben.

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Résumé On a employé la méthode deKirsten pour la détermination de l'azote de composés organiques contenant du fluor. On a introduit quelques légères modifications à la méthode originale.

     

Tricyclic-isoxazolidine analogues via intramolecular 1,3-dipolar cycloaddition reactions of nitrones

The tricyclic-isoxazolidine analogues tetrahydrothiochromenoisoxazoles, hexahydroisoxazolequinolines and tetrahydroisoxazolepyranopyridines were prepared by an intramolecular 1,3-dipolar cycloaddition reaction of a nitrone with an alkene. For N-alkylated hexahydroisoxazolequinolines, reduction of the reaction time from two days to 40 min was achieved using microwave heating. The cyclization to form tetrahydroisoxazolepyranopyridines only proceeded when the alkene was substituted with an electron withdrawing group.