Some expansions for integrals with weight functions

Two classes of expansions for integrals with arbitrary weight functions are derived. As one special case is obtained a generalization of Hermite's expansion. As a possible application is indicated the calculation of integrals with arbitrary weight functions.     

Regioselective formation of alkylidenecyclopropanes from 2-substituted cyclobutylidenes generated from geminal dibromocyclobutanes and methyllithium

Four different 2-substituted geminal dibromocyclobutanes were reacted with methyllithium at -78 degrees C. In contrast to previous studies using diazocyclobutanes as carbene precursors at temperatures above 200 degrees C via reaction of the corresponding tosylhydrazone sodium salts, the organometallic route in each case produces only an alkylidenecyclopropane that could be isolated in good yields. B3LYP calculations were employed to rationalize the observed regioselective ring contraction of the generated cyclobutyliden(oid)s. [reaction: see text]     

Molecular surface electrostatic potentials and local ionization energies of Group V–VII hydrides and their anions: Relationships for aqueous and gas-phase acidities

We have computed ab initio HF /6-31+G * electrostatic potentials and average local ionization energies on the molecular surfaces of the Group V–VII hydrides and corresponding anions of the first three rows of the periodic table. The surfaces were defined to be specified contours (0.002 or 0.001 au) of the molecular electronic density. The most negative potentials, V_S,min, and lowest ionization energies ī_S,min, were located and determined. Their magnitudes separately satisfy limited correlations with gas-phase protonation enthalpies and aqueous pK_a values. Our results indicate that V_S,min, and ī_S,min are complementary, the former reflecting electrostatic factors and the latter being related to charge transfer/polarization. More general relationships for protonation enthalpies are obtained when both V_S,min and ī_S,min are explicitly included. Solution-phase and gas-phase acidities are shown to correlate very well if electrostatic effects are explicitly taken into account. © 1993 John Wiley & Sons, Inc.     

New strategic reactions for organic synthesis: catalytic asymmetric C-H activation alpha to nitrogen as a surrogate for the mannich reaction

The asymmetric C-H activation reactions of methyl aryldiazoacetates are readily induced by the rhodium prolinate catalyst Rh(2)(S-DOSP)(4) (1) or the bridged prolinate catalysts Rh(2)(S-biDOSP)(2) (2a) and Rh(2)(S-biTISP)(2) (2b). The C-H activation of N-Boc-protected cyclic amines demonstrates that the donor/acceptor-substituted carbenoids display remarkable chemoselectivity, which allows for highly regioselective, diastereoselective, and enantioselective reactions to be achieved. Furthermore, the reactions can display high levels of double stereodifferentiation and kinetic resolution. The C-H activation is caused by a rhodium carbenoid induced C-H insertion. The potential of this chemistry is demonstrated by a very direct synthesis of threo-methylphenidate.     

Computational study of the amination of halobenzenes and phenylpentazole. A viable route to isolate the pentazolate anion?

Amination of halobenzenes, which proceeds via the benzyne intermediate (1), has been studied using quantum chemical methods. The computational data are in agreement with experimentally observed trends in reactivity and provide a qualitative explanation for the observed hydrogen isotope effects. To investigate if this is a viable way to isolate the pentazolate anion (2), the reactivities of the halobenzenes have been compared to phenylpentazole (3). The reaction energetics for phenylpentazole become favorable after complexation with Zn(2+).     

Screening for cyanobacterial hepatotoxins, microcystins and nodularin in environmental water samples by reversed-phase liquid chromatography-electrospray ionisation mass spectrometry

Water samples taken from 93 freshwater and brackish water locations in Aland (SW Finland) in 2001 were analysed for biomass-bound microcystins and nodularin, cyanobacterial peptide hepatotoxins, by liquid chromatography-mass spectrometry (LC-MS) in selected ion recording (SIR) and multiple reaction monitoring modes, HPLC-UV, and enzyme-linked immunosorbent assay (ELISA). The extracted toxins were separated on a short C18 column with a gradient of acetonitrile and 0.5% formic acid, and quantified on a Micromass Quattro Micro triple-quadrupole mass spectrometer with an electrospray ion source operated in the positive SIR or scan mode. An injection of 50 pg of microcystin-LR, m/z 995.5, on column gave a signal-to-noise ratio of 17 (peak-to-peak) at the chosen SIR conditions. In-source or MS-MS fragmentation to m/z 135.1, a fragment common to most microcystins and nodularin, was used for confirmatory purposes. Microcystins with a total toxin concentration equal to or higher than 0.2 microg l(-1) were confirmed by all three methods in water samples from 14 locations. The highest toxin concentration in a water sample was 42 microg l(-1). The most common toxins found were microcystins RR, LR and YR with different degrees of demethylation (non-, mono- or didemethylated). Parallel results achieved with ELISA and HPLC-UV were generally in good agreement with the LC-MS SIR results.     

Novel 1,3-dipolar cycloadditions of dinitraminic acid: implications for the chemical stability of ammonium dinitramide

Density functional theory at the B3LYP/6-31+G(d,p) level and ab initio calculations at the CBS-QB3 level have been used to analyze 1,3 dipolar cycloaddition reactions of dinitraminic acid (HDN) and its proton transfer isomer (HO(O)NNNO2). It is shown that the nitro group of HDN and the -N-N=O functionality of the isomer react readily with carbon-carbon double bonds. Cycloadditions of HDN are compared with the corresponding reactions with azides and nitrile oxides as 1,3 dipoles. It is shown that the reactivities of HDN and its proton transfer isomer decrease with increasing electron withdrawing power of the substituents adjacent to the carbon-carbon double bond. In contrast, for azides and nitrile oxides, the highest reactivity is obtained with dipolarophiles with strongly electron withdrawing substituents. The observed reactivity trends allow for the design of unsaturated compounds that are highly reactive toward azides and chemically inert toward dinitramides. This may be of relevance for the development of binder materials for ammonium dinitramide based propellants.