Pressure dependence and branching ratios in the decomposition of 1-pentyl radicals: shock tube experiments and master equation modeling

The decomposition and intramolecular H-transfer isomerization reactions of the 1-pentyl radical have been studied at temperatures of 880 to 1055 K and pressures of 80 to 680 kPa using the single pulse shock tube technique and additionally investigated with quantum chemical methods. The 1-pentyl radical was generated by shock heating dilute mixtures of 1-iodopentane and the stable products of its decomposition have been observed by postshock gas chromatographic analysis. Ethene and propene are the main olefin products and account for >97% of the carbon balance from 1-pentyl. Also produced are very small amounts of (E)-2-pentene, (Z)-2-pentene, and 1-butene. The ethene/propene product ratio is pressure dependent and varies from about 3 to 5 over the range of temperatures and pressures studied. Formation of ethene and propene can be related to the concentrations of 1-pentyl and 2-pentyl radicals in the system and the relative rates of five-center intramolecular H-transfer reactions and β C-C bond scissions. The 3-pentyl radical, formed via a four-center intramolecular H transfer, leads to 1-butene and plays only a very minor role in the system. The observed (E/Z)-2-pentenes can arise from a small amount of beta C-H bond scission in the 2-pentyl radical. The current experimental and computational results are considered in conjunction with relevant literature data from lower temperatures to develop a consistent kinetics model that reproduces the observed branching ratios and pressure effects. The present experimental results provide the first available data on the pressure dependence of the olefin product branching ratio for alkyl radical decomposition at high temperatures and require a value of <ΔE(down)(1000 K)> = (675 ± 100) cm(-1) for the average energy transferred in deactivating collisions in an argon bath gas when an exponential-down model is employed. High pressure rate expressions for the relevant H-transfer reactions and β bond scissions are derived and a Rice Ramsberger Kassel Marcus/Master Equation (RRKM/ME) analysis has been performed and used to extrapolate the data to temperatures between 700 and 1900 K and pressures of 10 to 1 × 10(5) kPa.     

Unconventional Secondary Structure Mimics: Ladder‐Rungs

Secondary structures tend to be recognizable because they have repeating structural motifs, but mimicry of these does not have to follow such well‐defined patterns. Bioinformatics studies to match side‐chain orientations of a novel hydantoin triazole chemotype ( 1 ) to protein‐protein interfaces revealed it tends to align well across parallel and antiparallel sheets, like rungs on a ladder. One set of these overlays was observed for the protein‐protein interaction uPA?uPAR. Consequently, chemotype 1 was made with appropriate side‐chains to mimic uPA at this interface. Biophysical assays indicate these compounds did in fact bind uPAR, and elicit cellular responses that affected invasion, migration, and wound healing.     

The enthalpy of formation of tungsten thiotetrafluoride

The enthalpy of hydrolysis of solid tungsten thiotetrafluoride, WF(in4)S, in aqueous sodium hydroxide solution is -528.2 kJ mo1^-1. Hence its standard enthalpy of formation has been calculated to be -1150.5 kJ mo1^-1.     

The stability of boundary conditions for an angled-derivative difference scheme

Tidal forcing of the shallow water equations is typical of a class of problems where an approximate equilibrium solution is sought by long time integration of a differential equation system. A combination of the angled-derivative scheme with a staggered leap-frog scheme is sometimes used to discretise this problem. It is shown here why great care then needs to be taken with the boundary conditions to ensure that spurious solution modes do not lead to numerical instabilities. Various techniques are employed to analyse two simple model problems and display instabilities met in practical computations; these are then used to deduce a set of stable boundary conditions.Dedicated to Professor J. Crank on the occasion of his 80th birthday     

The effective use of precision electroweak measurements

Bound state population dynamics in a diatom modelled by an appropriate Morse oscillator with a time-dependent well-depth is investigated perturbatively both in the absence and presence of high intensity radiation. For sinusoidally oscillating well-depth, the population of themth bound vibrational level,P _mm(t), is predicted to be a parabolic function of the amplitude of the oscillation of the well-depth (ΔD ₀) at a fixed laser intensity. For a fixed value of ΔD ₀,P _mm(t) is also predicted to be quadratic function of the field intensity (ɛ ₀). Accurate numerical calculations using a time-dependent Fourier grid Hamiltonian (TDFGH) method proposed earlier corroborate the predictions of perturbation theory. As to the dissociation dynamics, the numerical results indicate that the intensity threshold is slightly lowered if the well-depth oscillates. Possibility of the existence of pulse-shape effect on the dissociation dynamics has also been investigated.     

Solubilities and solvation of bis-(2,2′-bipyridyl)- and bis-(1,10-phenanthroline)dicyanoiron(II) in alcohols

Summary Solubilities of bis-(2,2-bipyridyl)- and bis-(1,10-phenanthroline)dicyanoiron(II) are reported for a range of primary aliphatic alcohols, from MeOH to 1-decanol. The established trends are compared with those for other solutes, and for the title compounds in H₂O-alcohol solvent mixtures.