Parviflorine,a glycosidic spirobenzylisoquinoline alkaloid

(+)-Parviflorine ($\text{1}$), found in $\text{Fumaria parviflora}$ Lam. (Fumariaceae), is the first known glycosidic spirobenzylisoquinoline alkaloid. Its acid hydrolysis yields (+)-parfumine ($\text{4}$) and D-glucose. Klyne's rule indicates that $\text{1}$ is a β-D-glucoside. The absolute configuration shown in expressions $\text{1-11}$ is predominant among spirobenzylisoquinolines. A generalization has been drawn between plant source and the oxygenation pattern of ring C for the spirobenzylisoquinoline alkaloids.     

Proton magnetic resonance spectra of substituted adamantane-2,4-diones. Determination of the C-6 and C-9 stereochemistry

The 220 MHz ¹H NMR spectra of 6-hydroxy-7-methyl-6-phenyladamantane-2,4-dione, 6-hydroxy-5,7-dimethyl-6-phenyladamantane-2,4-dione, and 6-hydroxy-7,9-dimethyl-6-phenyladamantane-2,4-dione have been determined and complete proton assignments carried out with the aid of multiple irradiation. The stereochemistry of the C-6 and C-9 chiral centres have been determined and some of the factors affecting the magnitude of the geminal, vicinal and W coupling constants are discussed.     

Comparison between the point-charge electrostatic model and the angular overlap model: The general case

The aim of this paper is to explore in detail the mathematical connection between the point-charge electrostatic model and the angular overlap model. More precisely, for any configuration nl^x in any symmetry, the matrix elements, and therefore the energy levels, as given by the angular overlap model restricted to the antibonding effects λ (for any of the possible λ's), are deduced from an effective potential constructed according to the point-charge electrostatic model. This allows us to give a mathematical proof of the equivalence between the point-charge electrostatic model and the angular overlap model taking into account all the antibonding effects λ. Finally, the sum rules for the angular overlap model are examined in the light of the formulae connecting the two models considered. Numerical tables for obtaining the results as given by the angular overlap model restricted to any of the antibonding effects from those as given by the point-charge electrostatic model are listed for the configurations nl^x with l = p, d, f and g.     

Editorial announcement

Editorial announcement     

Survey of reaction types in low-energy colliosional activation of protonated methyl alkyl ketones

In contrast to high-energy collisions, where simple cleavages are commoner, rearrangements typically account for 96–100% of products in low-energy collisions of the [M + 1]⁺ ions of aliphatic methyl ketones. Rules for predicting low-energy helium collsional-activated decomposition (CAD) spectra of the ketones are based on proton affinities of fragments formed by simple rearrangements. The commonest reaction is equivalent to the energetically improbable four-center 1,3-H or 1,3-R shift; other rearrangements equivalent to processes with five-, six-, or seven-center activated complexes are less important. In larger ions, loss of water followed by loss of alkene dominates. O-Protonated enol forms either lose water to give a carbonium ion that rearranges to forms capable of losing olefin fragments, or rearranges to an intermediate in the formation of acetyl ion and an alkane. O-Protonated keto forms rearrange to alkanes and protonated smaller carbonyl compounds. The ion kinetic energies necessary to produce several intense daughter ions at threshold establish the order of sequential fragmentations. When helium is the collisional gas and the ion energy is 30 eV in the laboratory frame (the maximum value studies), the ion energy is only 0.8–1.9 eV in the center-of-mass frame depending on its size. Only a fraction of this kinetic energy is converted to internal energy, so that onsets of reaction channels differing by several tenths of an electron-volt are easily studied. Some isomers of methyl ketones can be easily distinguished by He-CAD spectra of their [M + 1]⁺ ions.