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.     

Dahlberg's theorem in higher co-dimension

In 1977 the celebrated theorem of B. Dahlberg established that the harmonic measure is absolutely continuous with respect to the Hausdorff measure on a Lipschitz graph of dimension $n?1$ in ${\mathbb{R}}^n$, and later this result has been extended to more general non-tangentially accessible domains and beyond.In the present paper we prove the first analogue of Dahlberg's theorem in higher co-dimension, on a Lipschitz graph Γ of dimension d in ${\mathbb{R}}^n$, $d<n?1$, with a small Lipschitz constant. We construct a linear degenerate elliptic operator L such that the corresponding harmonic measure ${\omega }_L$ is absolutely continuous with respect to the Hausdorff measure on Γ. More generally, we provide sufficient conditions on the matrix of coefficients of L which guarantee the mutual absolute continuity of ${\omega }_L$ and the Hausdorff measure.     

Reaction kinetics and thermochemistry of the chemically activated and stabilized primary ethyl radical of methyl ethyl sulfide,CH3SCH2CH2•, with O2 to CH3SCH2CH2OO•

Oxidation of methyl ethyl sulfide (CH₃SCH₂CH₃, methylthioethane, MES) under atmospheric and combustion conditions is initiated by hydroxyl radicals, MES radicals, generated after loss of a H atom via OH abstraction, will further react with O₂ to form chemically activated and stabilized peroxyl radical adducts. The kinetics of the chemically activated reaction between the CH₃SCH₂CH₂• radical and molecular oxygen are analyzed using quantum Rice-Ramsperger-Kassel theory for k(E) with master equation analysis and a modified strong-collision approach to account for further reactions and collisional deactivation. Thermodynamic properties of reactants, products, and transition states are determined by the B3LYP/6-31+G(2d,p), M062X/6-311+G(2d,p), ωB97XD/6-311+G(2d,p) density functional theory, and CBS-QB3, G3MP2B3, and G4 composite methods. The reaction of CH₃SCH₂CH₂• with O₂ forms an energized peroxy adduct CH₃SCH₂CH₂OO• with a calculated well depth of 34.1 kcal mol⁻¹ at the CBS-QB3 level of theory. Thermochemical properties of reactants, transition states, and products obtained under CBS-QB3 level are used for calculation of kinetic parameters. Reaction enthalpies are compared between the methods. The temperature and pressure-dependent rate coefficients for both the chemically activated reactions of the energized adduct and the thermally activated reactions of the stabilized adducts are presented. Stabilization and isomerization of the CH₃SCH₂CH₂OO• adduct are important under high pressure and low temperature. At higher temperatures and atmospheric pressure, the chemically activated peroxy adduct reacts to new products before stabilization. Addition of the peroxyl oxygen radical to the sulfur atom followed by sulfur-oxygen double bond formation and elimination of the methyl radical to form S(= O)CCO• + CH₃ (branching) is a potentially important new pathway for other alkyl-sulfide peroxy radical systems under thermal or combustion conditions.     

Ranking Oxidant Sensitiveness: A Guide for Synthetic Utility

Common oxidants used in chemical synthesis, including newly developed perruthenates, were evaluated in the context of understanding (and better appreciating) the sensitiveness and associated potential hazards of these reagents. Analysis using sealed cell differential scanning calorimetry (scDSC) facilitated Yoshida correlations, which were compared to impact sensitiveness and electrostatic discharge experiments (ESD), that enabled sensitiveness ranking. Methyltriphenylphoshonium perruthenate (MTP3, 8 ), isoamyltriphenylphosphonium perruthenate (ATP3, 7 ) and tetraphenylphosphonium perruthenate (TP3, 9 ) were found to be the most sensitive followed by 2-iodoxybenzoic acid (IBX, 2 ) and benzoyl peroxide (BPO, 10 ), whereas the most benign were observed to be Oxone ( 12 ), manganese dioxide (MnO₂, 13 ), and N-bromosuccinimide (NBS, 17 ).