The 1,2,4-triazolyl cation: thermolytic and photolytic studies

The generation of the 1,2,4-triazolyl cation (1) has been attempted by the thermolysis and photolysis of 1-(1,2,4-triazol-4-yl)-2,4,6-trimethylpyridinium tetrafluoroborate (2) and the thermolysis of 1- and 4-diazonium-1,2,4-triazoles, using mainly mesitylene as the trapping agent. Thermolysis of 2 gave mostly 1,2,4-triazole, together with 3-(1,2,4-triazol-4-yl)-2,4,6-trimethylpyridine, 4-(1,2,4-triazol-4-ylmethyl)-2,6-dimethylpyridine, and 4-(2,4,6-trimethylbenzyl)-2,6-dimethylpyridine. Thermolysis of each of the diazonium salts in the presence of mesitylene again gave mainly triazole together with very low yields of 1-(1,2,4-triazol-1-yl)-2,4,6-trimethylbenzene and the corresponding -4-yl isomer in about the same ratio. On the other hand, photolysis of 2 in mesitylene gave mainly 1-(1,2,4-triazol-1-yl)-2,4,6-trimethylbenzene. A photoinduced electron transfer from mesitylene to 2 has been observed and preliminary laser flash photolyses of 2 and the corresponding 2,4,6-triphenylpyridinium salt have been carried out. The observed transients are explained as arising from the first excited states of the pyridinium salts rather than from 1. Ab initio MO calculations are reported and indicate that the predicted electronic ground-state of the triazolyl cation is a triplet state of B1 symmetry with five pi electrons, which corresponds to a diradical cation (1c). Possible mechanisms for the formation of the various products are proposed.     

Preparative gas chromatography of volatile metal compounds-I Separation of aluminium, chromium and iron beta-diketonates

The analytical gas chromatography of a range of fluorinated and unfluorinated beta-diketonates of aluminium, chromium and iron has been studied m detail and conditions have been established for their complete separation; the complexes of trifluoroacetylpivaloylmethane show the best characteristics for this purpose. A range of liquid phases and column conditions have been considered and Apiezon substrates have been shown to give optimal resolution. The technique has been extended to a preparative scale with up to 0.1-g chelate samples, and the efficiency of the process demonstrated by the removal of 2% proportions of two metal complexes from a sample of the third. Implications of the technique for the purification of metals are discussed.     

A comparative study of some lanthanon chelates of alizarin complexan as reagents for fluoride

A study has been made of the comparative suitability of the cerium^III, lanthanum and praseodymium chelates of alizarin complexan as reagents for the spectrophotometric determination of microgram amounts of fluoride. The cerium^III reagent is most sensitive at pH < 4.5 and the lanthanum reagent at pH 5.0. An enhancement of sensitivity may be obtained for both reagents at pH 4.3 by addition of acetone to 25 % v/v, but the most sensitive means of determination is to use the lanthanum reagent in aqueous solution at pH 5.2 with measurement at 281 mμ. This procedure is 200% more sensitive than the standard method at 620 mμ.     

Titrimetric determination of microgram amounts of bismuth after precipitation as Bi[Cr(SCN)(6)] followed by thiocyanate amplification

Bismuth (10-100 mug) is precipitated as Bi[Cr(SCN)(6)]. After filtration, the precipitate is treated with bicarbonate solution, and the thiocyanate dissolved is oxidized by iodine in alkaline medium to sulphate. After acidification, the excess of iodine is extracted into chloroform, and the iodide in the aqueous solution is amplified by bromine oxidation and subsequent treatment with more iodide. The titrimetric procedure provides 228 iodine atoms for each original bismuth ion. Only Hg(2+)(2), Hg(2+) and AsO(3-)(4) interfere seriously.     

Coordination properties of a diarylaza crown ether appended with a luminescent [Ru(bipy)3]2+ unit

The [Ru(bipy)(2)(1)](PF(6))(2) (bipy refers to 2,2'-bipyridine) complex, comprising a ruthenium(II) tris(2,2'-bipyridine) luminophore covalently linked to a di[(o-triethyleneglycoxy)phenyl]amine crown ether 1, has been synthesized and fully characterized. The photophysical properties of this metal complex have been examined in solution at ambient temperature. Luminescence from the metal complex is enhanced significantly in the presence of various adventitious cations, including protons. In particular, Li(+) cations bind to the crown ether, as evidenced by (1)H NMR and luminescence spectroscopy. Cation binding serves to decrease the rate of reductive quenching of the triplet state of the metal complex, thereby increasing the extent of luminescence. The solution-phase conformation of [Ru(bipy)(2)(1)](PF(6))(2), with and without encapsulated Li(+), has been examined by 2-D NMR and by molecular dynamics simulations.     

The microanalysis of fluorine-containing organic compounds

Summary Methods are described for the micro determination of chlorine, bromine, and iodine in organic compounds containing fluorine. The sample is heated with sodium in a nickel bomb, and the chloride ion produced is determined titrimetrically by a modified procedure involving the use of mercuric oxycyanide. Bromide is determined titrimetrically after oxidation to bromate with sodium hypochlorite; iodide is also determined by an amplified procedure after oxidation to iodate with bromine.The method has been extended to the simultaneous determination of chlorine, bromine, and iodine when present in organic compounds containing fluorine. All four halogens, and all possible combinations of halogens, can be determined in one compound after a single fusion.

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Zusammenfassung Es werden Methoden zur Mikrobestimmung von Chlor, Brom und Jod in fluorhaltigen organischen Substanzen beschrieben. Die Probe wird in einer Nickelbombe mit Natrium erhitzt. Das hierbei entstehende Chlorid wird mit Quecksilberoxycyanid nach einem modifizierten Verfahren titriert. Das Bromid wird nach Oxydation zu Bromat mit Natriumhypochlorit titriert. Das Jodid wird mit Brom zu Jodat oxydiert. Nach Zugabe von Jodid wird die sechsfache Jodmenge mit Thiosulfat bestimmt.Das Verfahren wurde für die gleichzeitige Bestimmung von Chlor, Brom und Jod in fluorhaltigen organischen Substanzen erweitert. Alle vier Halogene können somit unabhängig von ihrem gegenseitigen Verhältnis in einer Verbindung nebeneinander ineiner Einwaage bestimmt werden.

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Résumé Des méthodes sont décrites pour le microdosage du chlore, du brome, de l'iode dans les composés organiques contenant du fluor. L'échantillon est chauffé avec du sodium dans une bombe de nickel et l'ion chlorhydrique produit est déterminé titrimétriquement par une méthode modifiée mettant en jeu l'emploi d'oxycyanure mercurique. Le brome est dosé volumétriquement après oxydation en bromate a ec l'hypochlorite de sodium. L'iode est déterminé également par une methode amplifiée après oxydation en iodate par le brome.La méthode a été étendue au dosage simultané du chlore, du brome, de l'iode quand ils sont présents dans des composés organiques contenant du fluor. Les 4 halogènes et toutes les combinaisons possibles d'halogènes peuvent être déterminées sur un seul composé après une simple fusion.

     

Quantum qualitative dynamics

We describe our work on qualitative methods for visualizing the quantum eigenstates of systems with nonlinear classical dynamics. For two-degree-of-freedom systems, our approach is based on the use of generalized coherent states, and allows systems with nonoscillator kinematics to be investigated. The general approach is illustrated with two examples involving vibration-rotation interaction in polyatomic molecules. We apply the coherent states of the Lie groupH ₄SU(2) to define quantum surfaces of section for a model involving centrifugal coupling of a harmonic bend with molecular rotation, andSU(2)SU(2) coherent states to study two harmonic normal modes coupled to overall molecular rotation through coriolis interaction. In both systems, quantum states are visualized on the rotational surface of section and compared with the corresponding classical phase space structure. Striking classical-quantum correspondence is observed. We then describe recent results on the quantum states of (N 3)-dimensional systems of coupled nonlinear oscillators, which reveal a quantum delocalization that is reminiscent of classical Arnold diffusion.     

Vibrational spectroscopy of 3,4-difluorocyclobutenes: cis-d0, trans-d0 and trans-d4 species

Infrared and Raman spectra were recorded for cis-3,4-difluorocyclobutene (cDFCB) and trans-3,4-difluorocyclobutene-d4. Unscaled density functional theory (DFT) calculations of frequencies and intensities at the B3LYP/6-311++G(d,p) level supported the complete assignment of the vibrational fundamentals. The previous assignment of fundamentals of trans-3,4-difluorocyclobutene was revised. An unusual blue shift occurs for the methylenic CH-stretching frequencies of cis-3,4-difluorocyclobutene in going from the gas phase to the liquid phase. This hydrogen bond effect is related to similar observations recently reported and interpreted. The blue shift does not occur for the vinylic CH bonds of the cis isomer and does not occur for either type of CH bond in the trans isomer.     

Enantioselective synthesis of C2-functionalized, N-protected morpholines and orthogonally N,N'-protected piperazines via organocatalysis

In this Letter, we describe a novel three-step, one-pot procedure for the enantioselective synthesis of N-benzyl protected morpholines and orthogonally N,N'-protected piperazines with chiral alkyl groups installed at the C2 position of each heterocyclic core via organocatalysis. This methodology allows for the rapid preparation of functionalized morpholines and piperazines that are not readily accessible through any other chemistry in good to excellent % ee (55-98% ee).