Synthesis of a tetraazacyclotetradecadiene and a pentaazacyclotetradecatriene

Useful procedures for preparing a novel tetraazacyclotetradecadiene and a pentaazacyclotetradecatriene are reported. J. Heterocyclic Chem., 14, 1097 (1977)     

Regioselective uncatalysed hydrophosphination of alkenes: a facile route to P-alkylated phosphine derivatives

The synthesis of alkylarylphosphines is easily carried out by hydrophosphination of unactivated alkenes under mild thermal activation; gram scale amounts of products can be prepared by this simple methodology.     

Photodegradation of a 1,3,4-thiadiazole-urea herbicide. Isolation,characterization, X-ray crystal structure and synthesis of photoproducts

The photodegradation of 1,3-dimethyl-1-(2-(3-fluorobenzylthio)-1,3,4-thiadiazol-5-yl)urea as a thin film and in solution is described. The two photoproducts from thin-film photolysis were characterized by spectral and synthetic methods. The X-ray crystal structure of one of the photoproducts is also reported. The rearrangements were shown to involve an S-to-N benzyl migration, followed by a sulfur-oxygen substitution.     

Calculation of molecular geometries by SCF perturbation theory

An SCF perturbation method for investigating the effects of an arbitrary change in nuclear configuration on the electronic structure of a molecule is reported. Illustrative calculations for CO₂ and CH₃OH are presented. It is found that, when taken to second order, the error in the calculated change in energy which results from a change in nuclear configuration is typically in the range of 0.1 to 7%.     

Direct determination of cadmium at parts-per-billion level in waters by derivative atomic absorption spectrometry using atom trapping technique

A method has been described for the direct determinations of trace cadmium using derivative atom trapping flame atomic absorption spectrometry with an improved water-cooled stainless steel trapping equipment. The characteristic concentration (gave a derivative absorbance of 0.0044) and detection limit (3sigma) of cadmium were 0.028 and 0.02 ng ml(-1) when collecting for a 1 min, respectively, which were 992 and 145-fold better than those of the conventional flame atomic absorption spectrometry. The detection limit and sensitivity of the proposed method for a 2 min collection time were 1 and 2 orders of magnitude higher than those of conventional flame atomic absorption spectrometry. The present method was applied to the determinations of cadmium in water samples with a recovery range of 91 approximately 111% and a relative standard deviation of 4.7 approximately 5.6%.     

Suggested calculations using transition density matrices

It is suggested that certain transition density matrices, N-representable in a limit, be used in a variational calculation. It is noted that such trial matrices should yield reasonable values for the ground state energies of small atoms or molecules provided a set of overlap integrals is maximised.

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Zusammenfassung Es wird vorgeschlagen, bestimmte Übergangsdichtematrizen, die im Limit N-darstellbar sind, in einer Variationsrechnung zu benutzen. Es wird festgestellt, daß solche Näherungsmatrizen gute Werte für die Energie des Grundzustandes kleiner Atome oder Moleküle geben sollten, falls im Satz von Überlappungsintegralen maximiert wird.

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Résumé On propose d'utiliser dans un calcul variationnel certaines matrices densité de transition, N représentables à la limite. Ces matrices d'essai devraient fournir des valeurs raissonnables pour l'énergie de l'état fondamental dans les petits atomes et les petites molécules à condition de maximiser un ensemble d'intégrales de recouvrement.

     

Theoretical investigations of Fe porphyrins. V. Low-lying electronic states of bisammineporphinatoiron(III)

Ab initio CI calculations are reported on the lowest doublet, quartet, and sextet states of [Fe^III(P)(NH₃)₂]⁺. The low-spin ground state is calculated as (d_xy² (d_π)³ with d_xy(d_π)⁴ higher by 0.15 eV. The near-ir bands at ～1 eV observed in low-spin ferriheme proteins are attributed to (π → d_π) transitions. The lowest high-spin state is ⁶A_1g, and the near-ir transitions of the high-spin ferriheme proteins observed at ～1.2 eV are attributed to higher ⁶[tripsextet] excited states [i.e., ring triplet, metal sextet]. The 30-ps “triplet” transient populated with low quantum yield observed in laser-flash studies on Fe^III(TPP)CI [TPP = tetrapbenylporphyrin] may be an ¹[tripsextet] state.     

双核银络合物[Ag_2(dppm)_2(Py)_2(μ-Cl)]ClO_4的合成与结构

二-(二苯基膦)甲烷(dppm)是一种易与金属形成多核络合物的有机膦配体。我们用dppm作为配体合成了一系列银的多核络合物,并对其结构进行了研究。本文报导了其中一个双核化合物[Ag_2(dppm)_2(Py)_2(μ-Cl)]ClO_4的合成及晶体结构、分子结构的测定。     

The phenolic oxidation of a β-methylchalcone

The phenolic oxidation of 2',4-dihydroxy-4'-methoxy-β-methylchalcone using alkaline potassium ferricyanide gives an aurone rather than an isoflavone. This result is discussed in the context of current theories regarding the biosynthesis of flavonoid and isoflavonoid compounds.     

Effective asymmetric synthesis of 1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]indol-4-one (CBI)

A short, asymmetric synthesis of the 1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]indol-4-one (CBI) analogue of the CC-1065 and duocarmycin alkylation subunits is detailed that employs an effective enzymatic desymmetrization reaction of prochiral diol 12 using a commercially available Pseudomonas sp. lipase. The optically active monoacetate (S)-13 is furnished in exceptional conversions (88%) and optical purity (99% ee) and serves as an intermediate for the preparation of either enantiomer of CBI. Similarly, the Pseudomonas sp. lipase resolved the racemic intermediate 19, affording advanced intermediates of CBI in good conversions and optical purity (99% ee), and provided an alternative approach to the preparation of optically active CBI derivatives.