Radiative fusion from very symmetric reactions: the giant dipole resonance in the Au nucleus

The spectra of high-energy γ rays emitted by the Giant Dipole Resonance (GDR) built on moderately excited states associated with the evaporation of 0, 1 and 2 nucleons were measured in the ⁹⁰Zr + ⁸⁹Y symmetric fusion reaction. The radiative fusion data suggest statistical emission from the compound nucleus. In addition, the analysis of the high-energy γ-ray spectra associated with the different evaporation channels at the present temperature of 0.7 MeV and spin range 15–20 show a fairly narrow width of 5.0±0.35 MeV. This value is smaller than what would be expected in a nucleus where shell effects do not play a role.     

Kloosterman sums and traces of singular moduli

We give a new proof of some identities of Zagier relating traces of singular moduli to the coefficients of certain weakly holomorphic half integral weight modular forms. These identities play a central role in Zagier's work on the infinite product isomorphism introduced by Borcherds. In addition, we derive a simple expression for writing twisted traces of singular moduli as infinite series.     

A simple and versatile method to determine the enantiomeric purity of Diels-Alder adducts

The determination of the enantiomeric purity of Diels-Alder adducts derived from cyclopentadiene and a series of electron-deficient dienophiles is conveniently achieved by HPLC analysis on their 2,4-dinitrophenylhydrazine derivatives formed in one pot directly from the cycloaddition reaction.     

Curvature and wrinkling of premixed flame kernels—comparisons of OH PLIF and DNS data

The effects of curvature and wrinkling on the growth of turbulent premixed flame kernels have been investigated using both 2D OH planar laser-induced fluorescence (PLIF) and 3D direct numerical simulation (DNS). Comparisons of results between the two approaches show a high level of agreement, providing confidence in the simplified chemistry treatment employed in the DNS, and indicating that chemistry may have only a limited influence on the evolution of the freely propagating flame. This is in contrast to previous studies of the very early flame development where chemistry may be dominant. Statistics for curvature and wrinkling are presented in the form of probability density functions, and there is good agreement with previous findings. The limitations of 2D PLIF measurements of curvature are quantified by comparison with full 3D information obtained from the DNS. The usefulness of PLIF in providing data over a wide parameter range is illustrated using statistics obtained from both CH₄/air and H₂/air mixtures, which show a markedly different behaviour due to their different thermo-diffusive properties. The results provide a demonstration of the combined power of PLIF and DNS for flame investigation. Each technique is shown to compensate for the weaknesses of the other and to reinforce the strengths of both.     

Distinguishing and quantifying the torquoselectivity in competitive ring‐opening reactions using the stress tensor and QTAIM

Currently the theories to explain and predict the classification of the electronic reorganization due to the torquoselectivity of a ring‐opening reaction cannot accommodate the directional character of the reaction pathway; the torquoselectivity is a type of stereoselectivity and therefore is dependent on the pathway. Therefore, in this investigation we introduced new measures from quantum theory of atoms in molecules and the stress tensor to clearly distinguish and quantify the transition states of the inward (TSIC) and outward (TSOC) conrotations of competitive ring‐opening reactions of 3‐(trifluoromethyl)cyclobut‐1‐ene and 1‐cyano‐1‐methylcyclobutene. We find the metallicity ξ( r _b) of the ring‐opening bond does not occur exactly at the transition state in agreement with transition state theory. The vector‐based stress tensor response β_σ was used to distinguish the effect of the CN, CH₃, and CF₃ groups on the TSIC and TSOC paths that was consistent with the ellipticity ε, the total local energy density H( r_b ) and the stress tensor stiffness S_σ. We determine the directional properties of the TSIC and TSOC ring‐opening reactions by constructing a stress tensor space with trajectories (s) with length l in real space, longer l correlated with the lowest density functional theory‐evaluated total energy barrier and hence will be more thermodynamically favored. © 2016 Wiley Periodicals, Inc.     

Total synthesis of +/--hyphodermins A and D

An efficient formal synthesis of (+/-)-hyphodermins A and D, metabolites of Hyphoderma radula, has been completed in 12 and 11 steps, respectively. The tricyclic carbon skeleton of enone 6 was rapidly assembled from diester 11 via an alpha brominationn-elimination sequence followed by anhydride formation. Regioselective reduction of the lactone group of enone 6 with LiAlH(t-BuO) 3 gave lactol 15. Lactol 15 was converted in two steps to (+/-)-hyphodermin D, without the need for complex protection-deprotection strategies. Lactol 15 was converted in three steps to (+/-)-hyphodermin A, via the key step of epoxidation of an enone in the presence of a THP lactol. A combination of NMR and ab initio studies suggests that the structures of hyphodermin C and D should be interchanged.     

Complex phosphorus thermochemistry. Volume-based thermodynamics and the estimation of standard enthalpies of formation of gas phase ions: Delta(f)H(o) (PCl4+, g) and Delta(f)H(o) (PCl6-, g)

Energy-resolved collision-induced dissociation in a flowing afterglow-guided ion beam tandem mass spectrometer has recently enabled the accurate determination of the standard enthalpy of formation of the gaseous phosphorus pentachloride cation, Delta(f)H(o) ([PCl4(+)], g), found to be 414 +/- 17 kJ mol(-1) (giving a value of 378 +/- 18 kJ mol(-1) at 0 K). Such experimental values for the standard enthalpy of formation of gas phase complex are now being incorporated into the NIST standard reference data program. Such results, can, inter alia, provide a benchmark by which to test earlier computationally based methods which were made to estimate such quantities in the absence of any experimental data. The establishment of this value experimentally also affords us with the opportunity to explore the likely success of newer, simpler approaches. Previous large-scale direct minimization computations to estimate this (and other) standard enthalpies of formation match very well these new experimental results. This paper raises the question as to whether the much simpler volume-based thermodynamics (VBT) approach could yield equally satisfactory results and so circumvent, completely, the need for detailed modeling of the lattices involved. The conclusion is that the VBT approach portrays the extremely complex thermodynamics quite adequately. Thus for the purposes of obtaining basic thermodynamic data, complex modeling of the underlying structures involved may no longer be necessary. At least this should be the case for highly symmetrical ions, like PCl4(+), where detailed packing with counterions is possibly less important than in other cases and where covalent interactions (less easily modeled) with neighboring ions is unlikely to be strongly featured. Other gaseous complex ion enthalpies of formation are also predicted here.