Bis(dialkylmetal)-N,N′-dimethyloxamides of aluminium,gallium and indium,preparation, physical and spectroscopic properties

The reaction of N,N′-dimethyloxamide with trialkyl derivatives of aluminium, gallium, and indium yields bis(dialkylmetal) compounds of structural formula (R₂M)₂[O₂C₂(NCH₃)₂] (M = Al, Ga, In; and R = CH₃, C₂H₅). The M₂O₂C₂N₂ skeleton of these monomeric products forms an almost planar system of two fused five-membered rings, with S₂ symmetry. For the dimethylgallium and dimethylindium derivatives, ¹H and ¹³C NMR spectra show the presence of two conformational isomers which differ in the orientation of the N-methyl relative to the two metal-bound CH₃ groups.     

Synthesis of Tricyclic (λ5)-Phosphoranes; unusual N-demethylation/N-alkylation reactions during the oxidative addition of hexafluoroacetone and tetrachloro-ortho-benzoquinone to benzodiaza-λ3-phosphorinones. Single crystal X-ray diffraction studies of various products

The reaction of methylisatoic acid anhydride 1 with benzylamines led to the N-benzyl-N′-methylanthranilamide derivatives 2 – 4 . Their reaction with phosphorus trichloride furnished the 2-chloro-1-halobenzyl/benzyl-3-methyl-4(1 H)-1,3,2-benzodiazaphosphorin-4-ones 5 – 7 which, upon reaction with bis-(2-chloroethyl)ammonium chloride/triethylamine, were converted into the P-bis-(2-chloroethyl)amino-1-halobenzyl/benzyl-3-methyl-4(1 H)-1,3,2-benzodiazaphosphorin-4-ones 8 – 10 and 12 . With 2-chloroethylammonium chloride/triethyl-amine the P? NHCH₂CH₂Cl-substituted compound 11 was obtained from the P^IIICl-species 6 . The reaction of 8 – 10 and 12 with hexafluoroacetone (HFA) took an unusual course: apart from the oxidative addition of HFA and formation of the perfluoropinacolyl ring system, one of the two CH₂CH₂Cl groups was found to alkylate the CH₃N atom with formation of a five-membered (diazaphospholane) ring in the tricyclic phosphoranes 13 – 16 . The reaction of 11 with HFA also produced a spirophosphorane 17 which involved a λ⁵-oxazaphosphetidine ring system. In the reaction of 8, 10 and 12 with tetrachloro-o-benzoquinone, an oxidative addition reaction with concomitant N-alkylation and formation of the tricyclic phosphoranes 18 – 20 was found to take place. Single crystal X-ray structure determinations are described for the phosphoranes 13, 14 and 16 , and for the precursor compound 9 . The following features are common to the isostructural compounds 13 and 16 and the diethyl ether hemisolvate of 14 : the (λ⁵)-spiro phosphorus atom lies out of the plane of the other atoms of the rings to which it is common, and the dioxaphospholane rings display a twist conformation. In the λ³P-compound 9 the phosphorus atom also lies out of the plane of the other ring atoms.     

Absorption Spectra and Termination Kinetics of Transient Free Radicals in Solution Observed by UV./VIS. Spectroscopy with modulated excitation

Free radicals are generated in liquid solutions by harmonically modulated photolysis of suitable substrates. Harmonic analysis of the absorbance as functions of wavelength and modulation frequency yields the optical spectra and the decay kinetics of the transient species. The experimental technique and the analysis are described in detail. Results on t-butyl, 2-propyl and benzyl radicals generated by photolysis of the corresponding dialkyl resp. dibenzyl ketones are reported. They confirm previous spectral assignments and show that the termination reactions are diffusion controlled.     

Positive muons as probes in liquid phase free radical chemistry: Radical structures and reaction rates

Muonium-substituted organic free radicals are observed by muon spin rotation when positive muons are stopped in liquid unsaturated compounds. From muon precession frequencies in high external magnetic fields the isotropic muon-electron hyperfine coupling constants are determined. They lead to radical structure assignments. Results of a variety of projects are described which show thatSR can successfully complement conventional physical methods of free radical chemistry: A study of the temperature dependence of the coupling constants of isotopically substituted ethyl radicals yields information on structure and barriers to internal rotation. Rate constants for several radical reactions are extracted from the damping of theSR signals, in particular for unimolecular rearrangements and cis-trans-isomerizations. The theory for the analysis for the case of reversible site exchange is outlined.All results described here were obtained by E. Roduner, P. Burkhard and W. Strub of this laboratory, and B. Webster, M. Ramos and D. McKenna of the University of Glasgow. We all appreciate support from the Swiss National Foundation for Scientific Research, the National Institut for Scientific Investigations of Portugal, the Carnegie Trust for the Universities of Scotland, the Royal Society London and SIN.     

Determination of the average lifetime of bottom hadrons

We have determined the average lifetime of hadrons containing b quarks produced in e⁺e^? annihilation to be

$\text{τ}\text{B}\text{=}\text{1.83}\text{+0.83}\text{+0.37}\text{?}\text{?0.34}\text{×10}{}^{\mathrm{?12}}\text{s}$

. Our method uses charged decay products from both non-leptonic and semileptonic decay modes.     

Dynamics of vector spin glasses: The Gabay-Toulouse line

The dynamics of ann-component vector spin glass with infinite range interactions are investigated near and above the Gabay-Toulouse (GT) line. The local transverse susceptibility _T for 0 varies along the whole GT lineT _c1 (H) as ^v , with a field and temperature independent critical exponentv=1/2. The longitudinal susceptibility _L () remains analytic for all (T, H)T _c1 (H), except for a cross-over fromv=1 tov=1/2 forH0 at the freezing temperatureT=T _f . The dynamic susceptibilities _T () and _L () are already coupled above the GT line via self-energy terms. BelowT _c1 (H), this coupling is strongly enhanced by other mechanisms.     

Computational studies of carbon nanotube-hydrocarbon bond strengths at nanotube ends: effect of link heteroatom and hydrocarbon structure

Semiempirical and density functional electronic structure theory methods were used to study SWNT-X--R bond strengths, where the single-walled carbon nanotube (SWNT) had an armchair or zigzag structure, the link heteroatom X was O, N(H), or S and the hydrocarbon chain R was CH(2)CH(3), CH(OH)CH(3), CHCH(2), or CH(CF(3))CH(3). In all systems the hydrocarbon was bonded to the end of the nanotube. The SWNT-X--R bond (that is, the bond joining the link atom to the hydrocarbon) is more than 0.4 eV stronger for armchair than for zigzag nanotubes with the same diameters, irrespective of whether O, N, or S are used as link atoms or whether OH, C==C, or CF(3) groups are present in the hydrocarbon chain. This raises the possibility for selective manipulation of armchair/zigzag nanotubes using a variety of link atoms and hydrocarbon structures. The SWNT-O--CH(CF(3))CH(3) bond is weaker than the SWNT-O--CH(2)CH(3) bond (for both armchair and zigzag nanotubes), while inclusion of a double bond in the ethyl chain increases the bond strengths. Also, SWNT-S--CH(2)CH(3) and SWNT-N(H)--CH(2)CH(3) bonds are stronger than SWNT-O--CH(2)CH(3) bonds.     

Chromatographie von Carbamat- und Phenylharnstoff-Pesticiden auf Dünnschichten von basischem Zinkcarbonat

Thin layers of basic zinc carbonate can be used with good results for separation and multiple identification of carbamate and phenylurea pesticides. Five important substances could be separated by one-dimension TLC. The best results were obtained by the following developing solvents: a) benzene, b) a mixture of benzene/petroleum ether/chloroform (6∶1∶1). The substances are either recognisable in short-wave UV-light, when a fluorescence indicator (F 254 nm) is added, or in day-light, after spraying a solution of 0.1 N AgNO₃ in 3 N HNO₃, followed by an UV-exposure for about 4 min.     

Electrophilic Aromatic Substitution of Groups other than Hydrogen. Part I: Ipso Factors and Rate-Limiting Steps in Dehalogenations by Diazonium Ions. 26th communication on diazo coupling reactions

The rates of substitution of the group X in 1-X-2-naphthol-6-sulfonic acids (X = H, Cl, Br, and I) by p-chlorobenzenediazonium ions in aqueous solution have been measured. The rates of the halogenated naphthols relative to that of the parent compound (X = H) are 0.0070:0.0089:0.149 for X = Cl, Br, and I respectively. The reaction of 1-bromo-2-naphthol-6-sulfonic acid is catalysed by thiosulfate ions; the relative rate observed for this compound does not, therefore, represent the ipso factor. It is postulated that in its substitution the release of the electrofugal leaving group (Br^⊕) is rate-limiting.     

A novel spectroscopy using ultrafast two-pulse excitation of large polyatomic molecules

A first infrared pulse at frequency ν₁ interacts with vibrational states in S₀ and a second visible pulse at ν₂ promotes the excited molecules to the S₁ state from where they fluoresce. Tuning the frequency ν₂ over 600 cm^?1 allows the observation of a detailed spectrum which gives information on vibrational states in S₀ and on vibronic states in S₁ together with corresponding Franck—Condon factors. The spectra differ drastically from the common broad and featureless absorption and fluorescence bands.