Solvolytic behavior of p-dimethylamino-α-bromostyrene in water solutions

Nmr and UV studies show that $\text{p}$-dimethylamino-$\text{α}$-bromostyrene, I, undergoes S_Nl reaction in H₂O and HClO₄ (^kS_Nl = 6 × 10^?1sec.^?1 at 25°). The vinyl cation has an extraordinary selectivity for capture by aromatic amines relative to H₂O, including I itself to give the dimer II.     

GC–MS analysis of phenolic compounds in fuels after conversion to trifluoroacetate esters

The GC–MS characteristics of trifluoroacetate esters of phenolic compounds are discussed. Linear temperature programmed retention indices and total ion current MS response factors of over 120 phenolic esters are reported. The main GC advantages from analysis of trifluoroacetate esters as compared to plain phenols are enhanced volatility and improved resolution. For example, the elution temperature of a given phenol is typically 50 °C greater than that of the corresponding trifluoroacetate ester. Also, while retention of compounds with two trifluoroacetate groups is only moderately greater than mono esters, underivatized dihydroxy compounds are very difficult to elute from any GC column. Complete resolution of isomeric C₀-, C₁- and C₂-alkylphenol esters is readily achieved on conventional fused silica GC columns; resolution of the corresponding underivatized compounds requires specialized GC columns with low temperature limits. In general, mass spectra of trifluoroacetate esters are more characteristic of a given structure than those of the corresponding phenols and may be more rigorously interpreted towards structural elucidation. A table in the report summarizes some of the more important spectral features used in compound identification. Example applications in analysis of coal-, shale- and petroleum-derived materials are presented. Selected ion monitoring is used to determine individual phenolic components in whole distillates; reconstructed ion chromatograms are used to illustrate distributions of selected species as a function of fuel storage and thermal stress.     

The number of components in profile analysis tasks.

The central issue of this paper is how detection of a change in spectral shape depends on the number of components m that define the spectrum. First, a channel theory is reviewed and the predictions relating the detectability of such a change as a function of the number of components are derived. Second, the existing literature is reviewed. Most of it concerns the detection of an increment in a single tone of an m-component, equal-amplitude complex. The data are close (+/- 2 dB) to the predictions of the theory, which suggests that there is a relatively small change in threshold as the number of components increases. The consistency of the data is also discussed and hypotheses for discrepancies are presented. Finally, the results of an experiment measuring the detectability of a special spectral shape change is explored. In this case, all the changes are equal in size but some are opposite in sign, so that the summed change is zero. The results using this "balanced" spectral change are also consistent with the predictions of the theory and show that for this special kind of spectral change thresholds improve by nearly 7 dB as m increases from 4 to 24 components.     

Abbau von Palustrin zu (−)-Dihydropalustraminsäure ((2R, 6S, 1′S)-[6-(1′-Hydroxypropyl)-2-piperidyl]essigsäure) und Struktur von Palustrin und Palustridin. Mitteilung über Schachtelhalmalkaloide

Degradation of palustrin to (?)-dihydropalustramic acid ((2R,6S,1′S)-[6-(1′-hydroxypropyl)-2-piperidyl]acetic acid), and the structure of palustrin and palustridin The structure of the macrocyclic alkaloid palustrin is shown to be 1a . Its piperidine unit can be obtained as (?)-dihydropalustramic acid ( 6a ) by the following sequence of degradation reactions (Scheme 1): catalytic hydrogenation of 1a followed by methylation and Hofmann degradation provides the allyl base 4 . the regioselectivity of the Hofmann elimination is explained by intramolecular proton abstraction at C(3) by C(18)-O^?. Catalytic reduction of 4 and subsequent acidic hydrolysis yielded 6a and N, N-dimethylputrescine (?N,N-dimethyl-1,4-butanediamine; 7 ). Loss of the N-alkyl group in the formation of 6a occurs during the catalytic hydrogenation step. This interpretation is supported by the results of model experiments. The position of the double bond in 1a is deduced from the IR. spectrum of the bromo-δ-lactone 19 prepared by treatment of 1a with N-bromosuccinimide at pH 4 (Scheme 3). Some of our previously published results on the degradation of dihydropalustrin ( 2a ) are obviously at variance with the newly proposed structure for palustrin ( 1a ). They can easily be explained by assuming a partial hydrogenolysis of the C(17)-N(1) bond during the preparation of dihydropalustrin from palustrin. Periodate cleavage of dihydropalustramic acid methyl ester ( 6b ) liberates propionaldehyde, which can be trapped by working at pH 7.5 (Scheme 2); at lower pH values it condenses rapidly with the simultaneously generated 3,4,5,6-tetrahydropyridine derivative 15 . The structure of the condensation product is proposed to be 16 on the basis of the isolation of its hydrogenation product, an isomeric dihydropalustramic acid ( 17 ).     

Effects of high intensity ultrasound on inorganic solids

Ultrasonic irradiation dramatically affects the reactivity of a variety of inorganic solids. We have found, for example, large increases in the rates of intercalation of a wide range of compounds into various layered inorganic solids (such as ZrS2, V2O5, TaS2 and MoO3. High intensity ultrasound also enhances the heterogeneous catalysis of alkene hydrogenation by Ni powders. Scanning electron microscopy reveals that ultrasound has multiple effects on the morphology and surface characteristics of inorganic solids, creating substantial surface damage, increasing surface areas significantly and causing increased particle aggregation.     

Ultraviolet properties of maximal supergravity

We argue that recent results in string perturbation theory indicate that the four-graviton amplitude of four-dimensional N=8 supergravity might be ultraviolet finite up to eight loops. We similarly argue that the h-loop M-graviton amplitude might be finite for h<7+M/2.     

Improved estimation of PM2.5 brown carbon contributions to filter light attenuation

Multiwavelength light attenuation measurements have been acquired as part of thermal/optical carbon analysis in the U.S.Chemical Speciation Network(CSN)and the ...     

Glass transition of miscible binary polymer-polymer thin films

The average glass transition temperatures, Tg, of thin homopolymer films exhibit a thickness dependence, Tg(h), associated with a confinement effect and with polymer-segment-interface interactions. The Tg's of completely miscible thin film blends of tetramethyl bisphenol-A polycarbonate (TMPC) and deuterated polystyrene (dPS), supported by SiO(x)/Si, decrease with decreasing h for PS weight fractions phi >0.1. This dependence is similar to that of PS and opposite to that of TMPC thin films. Based on an assessment of Tg(h, phi), we suggest that the Tg(h, phi) of miscible blends should be rationalized, additionally, in terms of the notion of a self-concentration and associated heterogeneous component dynamics.