Differentiation of species of the Baccharis genus by HPLC and chemometric methods.

Phytochemical investigation of the aerial parts of three Baccharis species (Asteraceae family) was performed using HPLC and chemometric methods, with the objective of distinguishing between three morphologically very similar species: Baccharis genistelloides Persoon var. trimera (Less.) DC, B. milleflora (Less.) DC and B. articulata (Lam.) Persoon. With the help of Principal Component Analysis (PCA) and variance weights, it was possible to characterize the chromatographic profiles of the alcoholic extracts of the three species. Application of Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN) methods on a training set of 74 extracts resulted in models that correctly classified all eight samples in an independent test set.     

Voltammetric determination of methyl parathion, ortho, meta and para nitrophenol with a carbon paste electrode modified with C18

Summary The determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C₁₈. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s^–1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml^–1 for ONP, 5 ng ml^–1 for MNP, 4.3 ng ml^–1 for PNP and 7.9 ng ml^–1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.     

Mass spectra of bile acid methyl ester acetate derivatives

Deuterium labeling in the acetate derivatives of cholic acid demonstrates that electron impact induced consecutive loss of HOAc from the molecular ion occurs in the following order of decreasing preference: 12α-OAc > 7α-OAc > 3α-OAc. Numerous examples are presented showing that consecutive loss of HOAc from a common ion generally increases progressively with relative intensity. In the acetate pregnan-20-one derivatives of cholic acid, loss of 43 mass units from the molecular ion comes from the 12α-OAc and not the 17β-acetyl sidechain. Ketene is ejected from an acetoxy group located in an α position to a carbonyl on which an ion-radical charge is localized.     

A formula periodic table for benzenoid hydrocarbons and the aufbau and excised internal structure concepts in benzenoid enumerations

The genesis of the aufbau and excised internal structure concepts is traced. These concepts were pivotal to the first published enumerations of the strictly peri-condensed, non-Kekuléan, and essentially strain-free total resonant sextet benzenoid groups. Aperiodic table set is defined as a partially ordered set forming a two-dimensional array which complies with thetriad principle where a central element has a metric property that is the arithmetic mean of two adjacent surrounding member elements.     

A theoretical study of π-hydrocarbon-iron tricarbonyl complexes

The molecular orbital parameters for tricarbonyl(tetrahapto-unsaturated-hydrocarbon)iron complexes are computed using graph-theoretical methods. The results are in agreement with their experimental properties.     

Efficient palladium-catalyzed nucleophilic addition of triorganoindium reagents to carbocyclic derivatives

Palladium (0)-catalyzed allylic substitution reactions employing triorganoindium reagents have been investigated. In situ generated vinyl- and arylindiums react with substituted and unsubstituted cyclohex-2-enyl esters in the presence of 1-3 mol % Pd(2)(dba)(3) to produce vinyl- or arylcyclohexenes in moderate to excellent yields. The stereoselectivity of this process was also examined, and evidence is presented that the reaction proceeds with inversion of stereochemical configuration.     

Metal derivatives of azoles,part VII. Pyrazolato-bridged dinuclear complexes containing either cyclopalladated or -platinated trimesitylphosphine or -arsine

Summary The halogen bridges of the dimeric, cyclometallated trimesityl-arsine and -phosphine complexes of palladium(II) and platinum(II), where M=Pd or Pt and E=P or As have been replaced with pyrazolate groups to give the corresponding and less symmetric pyrazolato-bridged complexes, where M=Pd or Pt, E=P or As, Pz=pyrazolato anion, and M=Pd, E=As, Pz=3,5-dimethylpyrazolato anion. In the case of the palladium complexes,¹H. n.m.r. clearly indicates the presence of only one isomer which is most likely to have thetrans configuration while the platinum complexes are mixtures of bothcis andtrans forms.Part VI, ref. 3c     

The reaction of N-aminophthalimide with isothiocyanates

N-Aminophthalimide ( I ) reacted in refluxing isopropyl alcohol with a number of isothiocyanates to give the related 1:1 addition products, N-(3-substitutedthioureido)phthalimides III. On the other hand, heating I directly with an excess of neat arylisothiocyanates produced the N-arylphthalimides IV. As shown for IIIa, the 1:1 addition products are conveniently deblocked by the Ing-Manske procedure to yield the 4-substituted thiosemicarbazide.