Transverse Polarisation of Quarks in Hadrons

We review the present state of knowledge regarding the transverse polarisation (or transversity) distributions of quarks. After some generalities on transverse polarisation, we formally define the transversity distributions within the framework of a classification of all leading-twist distribution functions. We describe the QCD evolution of transversity at leading and next-to-leading order. A comprehensive treatment of non-perturbative calculations of transversity distributions (within the framework of quark models, lattice QCD and QCD sum rules) is presented. The phenomenology of transversity (in particular, in Drell-Yan processes and semi-inclusive leptoproduction) is discussed in some detail. Finally, the prospects for future measurements are outlined.Comment: small changes, references added, as finally published in Physics Report

The concept of transport capacity in geomorphology

The notion of sediment-transport capacity has been engrained in geomorphological and related literature for over 50 years, although its earliest roots date back explicitly to Gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering. Despite cross fertilization between different process domains, there seem to have been independent inventions of the idea in aeolian geomorphology by Bagnold in the 1930s and in hillslope studies by Ellison in the 1940s. Here we review the invention and development of the idea of transport capacity in the fluvial, aeolian, coastal, hillslope, débris flow, and glacial process domains. As these various developments have occurred, different definitions have been used, which makes it both a difficult concept to test, and one that may lead to poor communications between those working in different domains of geomorphology. We argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons. First, as sediment becomes entrained in a flow, the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment. Secondly, environmental sediment transport is complicated, and the range of processes involved in most movements means that simple relationships are unlikely to hold, not least because the movement of sediment often changes the substrate, which in turn affects the flow conditions. Thirdly, the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space. Consequently, new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

Reactions of Stable N-Heterocyclic Silylenes with Ketones and 3,5-Di-tert-butyl-o-benzoquinone

Azhakar R, Ghadwal R, Roesky HW, Hey J, Stalke D. Reactions of Stable N-Heterocyclic Silylenes with Ketones and 3,5-Di-tert-butyl-o-benzoquinone. Organometallics. 2011;30(14):3853-3858

Facile Access to Transition-Metal-Carbonyl Complexes with an Amidinate-Stabilized Chlorosilylene Ligand

Azhakar R, Ghadwal R, Roesky HW, Hey J, Stalke D. Facile Access to Transition-Metal-Carbonyl Complexes with an Amidinate-Stabilized Chlorosilylene Ligand. Chemistry - An Asian Journal. 2012;7(3):528-533.Three transition‐metal–carbonyl complexes [V(L)(CO)3(Cp)] (1), [Co(L)(CO)(Cp)] (2), and [Co(L2)(CO)3]+[CoCO)4]− (3), each containing stable N‐heterocyclic‐chlorosilylene ligands (L; L=PhC(NtBu)2SiCl) were synthesized from [V(CO)4(Cp)], [Co(CO)2(Cp)], and Co2(CO)8, respectively. Complexes 1, 2, 3 were characterized by NMR and IR spectroscopy, EI‐MS spectrometry, and elemental analysis. The molecular structures of compounds 1, 2, 3 were determined by single‐crystal X‐ray diffraction

Double N–H bond activation of N,N′-bis-substituted hydrazines with stable N-heterocyclic silylene

Azhakar R, Ghadwal R, Roesky HW, Hey J, Stalke D. Double N–H bond activation of N,N′-bis-substituted hydrazines with stable N-heterocyclic silylene. Dalton Trans. 2012;41(5):1529-1533.The reaction of N-heterocyclic silylene (NHSi) L [L = CH{(C[double bond, length as m-dash]CH2)(CMe)(2,6-iPr2C6H3N)2}Si] with benzoylhydrazine, 1,2-dicarbethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-butoxycarbonyl)hydrazine in 1 : 1 molar ratio resulted in compounds 1–4 with an almost quantitative yield and five coordinate silicon atoms. Compounds 1–4 were formed by double N–H bond activation by deliberate selection of N,N′-bis-substituted hydrazine compounds bearing the –C(O)NHNH– unit. Compounds 1–4 were characterized by NMR spectroscopy, EI-MS and elemental analysis. The molecular structures of compounds 1–3 were unambiguously established by single crystal X-ray structural analysis

Mixed valence η6-arene cobalt(i) and cobalt(ii) compound

Azhakar R, Ghadwal R, Roesky HW, Hey J, Krause L, Stalke D. Mixed valence η6-arene cobalt(i) and cobalt(ii) compound. Dalton Transactions. 2013;42(28): 10277.The first carbonyl free mixed valence cobalt(I)/cobalt(II) compound [2{L2Co(I)(η6-C7H8)}]2+ [Co(II)2Cl6]2− (1) [L = PhC(NtBu)2SiCl] was obtained by the reaction of four equivalents of anhydrous CoCl2 with five equivalents of N-heterocyclic chlorosilylene L. In contrast, the reaction of L with CoBr2 yielded [L2CoBr2] (2). Compound 1 was formed by the cleavage of Co–Cl bonds, the reduction of Co(II) to Co(I) and by the coordination of a toluene molecule. The chlorosilylene (L) functions as a reducing agent as well as a neutral σ-donor ligand. The toluene molecule coordinates to the Co(I) atom in an η6-fashion

Heteroaromaticity approached by charge density investigations and electronic structure calculations

In this paper we present the results of a high-resolution single crystal X-ray diffraction experiment at 15 K on a benzothiazol-substituted phosphane and a subsequent charge density study based on multipole refinement and a topological analysis according to Bader's quantum theory of atoms in molecules. Although two valence shell charge concentrations (VSCCs) in the non-bonding region of each phosphorus and sulfur atom were found, the integration of both heteroatomic basins emphasizes charge depletion. Nevertheless they are attractive for C-H center dot center dot center dot P and C-H center dot center dot center dot S hydrogen bonding in the solid state. The nature of the P-C bonds and the question of aromaticity in the heterocycles were subject to our investigations. The ellipticities along the bonds were analysed to approach delocalization. The source function is employed to visualise atomic contributions to aromaticity. Theoretical calculations have been carried out to compute nuclear chemical shifts, induced ring currents and a variety of delocalization indices. All applied measures for delocalization point in the same direction: while heteroaromaticity is present in the benzothiazolyl substituents, the bridging P-C bonds are only involved marginally, almost preventing total conjugation of the phosphane. The charge density distributions around the phosphorus and the sulfur atoms have very similar features but turn out to be chemically very different from each other. Commonly used simplifying concepts have difficulties in providing a comprehensive view on the electronic situation in the molecule. Our results raise doubts on the validity of the common interpretation of VSCCs as one-to-one representations of Lewis lone pairs

A Remarkable End-On Activation of Diazoalkane and Cleavage of Both C–Cl Bonds of Dichloromethane with a Silylene to a Single Product with Five-Coordinate Silicon Atoms

The 1:1 reaction of benzamidinato-stabilized chlorosilylene PhC­(N<i>t</i>Bu)₂SiCl (<b>1</b>) with CH­(SiMe₃)­N₂ resulted in the formation of colorless [PhC­(N<i>t</i>Bu)₂Si­(Cl)­{N₂CH­(SiMe₃)}]₂ (<b>2</b>), which consists of a four-membered Si₂N₂ ring. Surprisingly, N₂ elimination from the diazoalkane did not occur, but rather an end-on activation of the nitrogen was observed. For the mechanism, we propose the formation of a silaimine complex <b>A</b> as an intermediate, which is formed during the reaction and dimerized under [2 + 2] cycloaddition to <b>2</b>. In contrast, treatment of <b>1</b> with dichloromethane afforded a 2:1 product, [{PhC­(N<i>t</i>Bu)₂Si­(Cl₂)}₂CH₂] (<b>3</b>), which is obviously formed by oxidative addition under cleavage of both C–Cl bonds and formation of two Si–Cl and two Si–C bonds. Both silicon atoms in <b>3</b> are five-coordinate. Compounds <b>2</b> and <b>3</b> were characterized by single-crystal X-ray studies, multinuclear NMR spectroscopy, and EI-mass spectrometry