The thermal decomposition of fluorinated esters. II. The effect of γ-substitution

The gas-phase kinetics of thermal decomposition of ethyl difluoroacetate, pentafluoropropionate, and hepatfluorobutyrate have been studied. The normal ester decomposition route to ethylene plus carboxylic acid is taken in each case, but the fluorinated acids decompose rapidly at the temperatures used. The primary decompositions are homogeneous and unimolecular, and the three Arrhenius equations are The postulate of a slightly electron-rich γ carbon in six-center ester transition states is supported by the higher rates and lowered activation energies observed when increasingly electron-withdrawing fluorinated groups are linked to this center. The stabilization is reflected in a ρ constant of +0.30. The results are compared with previous work on α substitution in fluorinated esters.     

Martingales,the smoothing index and ergodic theory

A classical theorem of Meyer Jerison which shows that the convergence in the pointwise ergodic theorem is equivalent to the convergence of an associated martingale is expanded to a conditional setting. An equiconvergence theorem of the type established for martingales by N.F.G. Martin and E. Boylan is established in the ergodic case for an ergodic, non-invertible, measure-preserving transformation.     

Synthesis of a carbasugar analogue of a putative intermediate in the UDP-galp-mutase catalyzed isomerization

[reaction: see text] The synthesis of the carbasugar analogue of 1,4-anhydro-beta-d-galactopyranose, a proposed intermediate in the reaction catalyzed by uridine diphosphate-alpha-d-Galp mutase, in racemic form via Diels-Alder and Barton decarboxylation chemistry is reported. This compound was found not to inhibit the mutase from Mycobacterium tuberculosis, indicating that the enzyme does not possess a 1,4-anhydro-beta-d-galactopyranose binding pocket.     

Parity-violating electron deuteron scattering and the proton's neutral weak axial vector form factor

We report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles at Q2=0.038 (GeV/c)2. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry A=-3.51+/-0.57 (stat)+/-0.58 (syst) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also consistent with theoretical predictions.     

Total synthesis of ingenol

A total synthesis of the biologically important diterpene ingenol has been completed. Ring-closing olefin metathesis was used to construct the strained "inside-outside" tetracyclic skeleton, and a series of diastereoselective reactions were employed to complete the synthesis. Another naturally occurring ingenane, 20-deoxyingenol, has also been prepared.     

Macrocyclic diiminodipyrromethane complexes: structural analogues of Pac-Man porphyrins

The complexation of palladium(II) by a unique family of [2+2] diiminodipyrromethane macrocycles yields compounds that adopt structures reminiscent of Pac-Man porphyrins.     

Minimal Length Elements of Thompson's Group F

Elements of the group are represented by pairs of binary trees and the structure of the trees gives insight into the properties of the elements of the group. The review section presents this representation and reviews the known relationship between elements of F and binary trees. In the main section we give a method of determining the minimal lengths of elements of Thompson's group F in the two generator presentation

Long-memory in an order-driven market

This paper introduces an order-driven market with heterogeneous investors, who submit limit or market orders according to their own trading rules. The trading rules are repeatedly updated via simple learning and adaptation of the investors. We analyze markets with and without learning and adaptation. The simulation results show that our model with learning and adaptation successfully replicates long-memories in trading volume, stock return volatility, and signs of market orders in an informationally efficient market. We also discuss why evolutionary dynamics are important in generating these features.     

Solid energy calibration standards for P K‐edge XANES: electronic structure analysis of PPh4Br

P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy is a powerful method for analyzing the electronic structure of organic and inorganic phosphorus compounds. Like all XANES experiments, P K‐edge XANES requires well defined and readily accessible calibration standards for energy referencing so that spectra collected at different beamlines or under different conditions can be compared. This is especially true for ligand K‐edge X‐ray absorption spectroscopy, which has well established energy calibration standards for Cl (Cs₂CuCl₄) and S (Na₂S₂O₃·5H₂O), but not neighboring P. This paper presents a review of common P K‐edge XANES energy calibration standards and analysis of PPh₄Br as a potential alternative. The P K‐edge XANES region of commercially available PPh₄Br revealed a single, highly resolved pre‐edge feature with a maximum at 2146.96 eV. PPh₄Br also showed no evidence of photodecomposition when repeatedly scanned over the course of several days. In contrast, we found that PPh₃ rapidly decomposes under identical conditions. Density functional theory calculations performed on PPh₃ and PPh₄⁺ revealed large differences in the molecular orbital energies that were ascribed to differences in the phosphorus oxidation state (III versus V) and molecular charge (neutral versus +1). Time‐dependent density functional theory calculations corroborated the experimental data and allowed the spectral features to be assigned. The first pre‐edge feature in the P K‐edge XANES spectrum of PPh₄Br was assigned to P 1s → P‐C π* transitions, whereas those at higher energy were P 1s → P‐C σ*. Overall, the analysis suggests that PPh₄Br is an excellent alternative to other solid energy calibration standards commonly used in P K‐edge XANES experiments.