Complete 1H NMR assignments of pyrrolizidine alkaloids and a new eudesmanoid from Senecio polypodioides

Chemical investigation of the aerial parts of Senecio polypodioides lead to the isolation of the new eudesmanoid 1β‐angeloyloxyeudesm‐7‐ene‐4β,9α‐diol ( 1 ) and the known dirhamnosyl flavonoid lespidin ( 3 ), while from roots, the known 7β‐angeloyloxy‐1‐methylene‐8α‐pyrrolizidine ( 5 ) and sarracine N‐oxide ( 6 ), as well as the new neosarracine N‐oxide ( 8 ), were obtained. The structure of 1 and 8 was elucidated by spectral means. Complete assignments of the ¹H NMR data for 5 , 6 , sarracine ( 7 ), and 8 were made using one‐dimensional and two‐dimensional NMR experiments and by application of the iterative full spin analysis of the PERCH NMR software. Copyright © 2014 John Wiley & Sons, Ltd.     

Braided Logic: The Simplest Models

The only pair of binary classical essential connectives for which the Artin braid relation holds is a distributive lattice, i.e. the Boolean disjunction and conjunction of     

Solvent effects on substitution reactions at complexes of the [Fe(CN)5L]3- type in binary aqueous mixtures

Summary The kinetics of replacement of 4,4-bipyridine, (4,4-bipy), and 4-cyanopyridine, (4-CNpy), by cyanide in [Fe(CN)₅-(4,4-bipy)]^3-. at 298 K have been studied in binary aqueous mixtures containing different amounts of t-butanol, methanol, glycerol, ethyleneglycol and sucrose. The plots of logarithms of the limiting rate constantsversus the mole fraction of water are linear over the entire composition range studied, showing the importance of solvation phenomena. A different straight line of log (k_L/s^–1)versus X_H2O is obtained for each mixture, indicating the influence of other solvent parameters on the reaction rate. A multiparameter regression of G _exp with A (acidity vector), B (basicity vector) and G^E is used for both reactions; plots of G _calc versus G _exp are linear with slopes of near unity.     

Volumes of activation for dissociation of pentacyanoferrates(II) through pressure and salt effects on reactivity

Summary Dependences of rate constants on pressure (up to 1 kbar) and on added salt concentration (up to 6.0 mol dm^–3 LiNO₃, NaNO₃, NaCl, Na₂SO₄ or KNO₃) have been established for dissociative substitution of pentacyanoferrates(II), [Fe(CN)₅L]^3– with L = 4-cyanopyridine, 4,4-bipyridyl, 4-phenylpyridine and 4-t-butylpyridine. Activation volumes derived directly from pressure effects, and indirectly from salt effects via surface tension dependences and derived surfaces of activation, are reported, compared and discussed.     

Absolute configuration of diterpenoids from Jatropha dioica by vibrational circular dichroism

The absolute configuration of jatropholone A 1 and B 2, including the possibility to observe the vibrational circular dichroism (VCD) capacity to differentiate between two epimeric compounds in the presence of an inherently dissymmetric chromophore, which normally dominates VCD and electronic circular dichroism (ECD) spectra, followed after comparison of their experimental and DFT calculated VCD spectra, allowed us to conclude that although non-local (M/P) chirality generated by atropisomerism dominates over local chirality generated by an (R/S) change, the stereogenic center can confidently be assigned by VCD after DFT calculations. In addition, the absolute configurations of jatrophatrione 3 and citlalitrione 4, a compound proposed as a taxonomic marker for the genus Jatropha, were assigned by contrasting their respective calculated and experimental IR and VCD spectra. The evaluation of Flack and Hooft parameters obtained from the single-crystal X-ray diffraction data of jatropholone B acetate 6, and of 4 independently confirmed the absolute configurations of these molecules.