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  • 2005-2009
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  • 1
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    On Non-Rank Facets of Stable Set Polytopes of Webs with Clique Number Four (2003)
    Details
    Publication Date: 2014-11-10
    Description: Graphs with circular symmetry, called webs, are relevant w.r.t. describing the stable set polytopes of two larger graph classes, quasi-line graphs and claw-free graphs. Providing a decent linear description of the stable set polytopes of claw-free graphs is a long-standing problem. However, even the problem of finding all facets of stable set polytopes of webs is open. So far, it is only known that stable set polytopes of webs with clique number $\leq 3$ have rank facets only while there are examples with clique number $〉4$ having non-rank facets.
    Keywords: ddc:000
    Language: English
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  • 2
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    Multiscale Analysis for the Bio-Heat Transfer Equation (2003)
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    Publication Date: 2014-02-26
    Description: The bio-heat transfer equation is a macroscopic model for describing the heat transfer in microvascular tissue. In [{\sl Deuflhard, Hochmuth 2002}] the authors applied homogenization techniques to derive the bio-heat transfer equation as asymptotic result of boundary value problems which provide a microscopic description for microvascular tissue. Here those results are generalized to a geometrical setting where the regions of blood are allowed to be connected. Moreover, asymptotic corrector results are derived.
    Keywords: ddc:000
    Language: English
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  • 3
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    Polyhedral Investigations on Stable Multi-Sets (2003)
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    Publication Date: 2014-11-10
    Description: Stable multi-sets are an evident generalization of the well-known stable sets. As integer programs, they constitute a general structure which allows for a wide applicability of the results. Moreover, the study of stable multi-sets provides new insights to well-known properties of stable sets. In this paper, we continue our investigations started in [{\sl Koster and Zymolka 2002}] and present results of three types: on the relation to other combinatorial problems, on the polyhedral structure of the stable multi-set polytope, and on the computational impact of the polyhedral results. First of all, we embed stable multi-sets in a framework of generalized set packing problems and point out several relations. The second part discusses properties of the stable multi-set polytope. We show that the vertices of the linear relaxation are half integer and have a special structure. Moreover, we strengthen the conditions for cycle inequalities to be facet defining, show that the separation problem for these inequalities is polynomial time solvable, and discuss the impact of chords in cycles. The last result allows to interpret cliques as cycles with many chords. The paper is completed with a computational study to the practical importance of the cycle inequalities. The computations show that the performance of state-of-the-art integer programming solvers can be improved significantly by including these inequalities.
    Keywords: ddc:000
    Language: English
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  • 4
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    Formation and structure of quasi-static cloud-layers in brown dwarf atmospheres (2003)
    Details
    Publication Date: 2014-02-26
    Description: In this paper, first solutions of the dust moment equations developed in [{\sl Woitke & Helling 2002}] for the description of dust formation and precipitation in brown dwarf and giant gas planet atmospheres are presented. We consider the special case of a static brown dwarf atmosphere, where dust particles continuously nucleate from the gas phase, grow by the accretion of molecules, settle gravitationally and re-evaporate thermally. Applying a kinetic description of the relevant microphysical and chemical processes for TiO$_2$-grains, the model makes predictions about the large-scale stratification of dust in the atmosphere, the depletion of molecules from the gas phase, the supersaturation of the gas in the atmosphere as well as the mean size and the mass fraction of dust grains as function of depth. Our results suggest that the nucleation occu in the upper atmosphere where the gas is cool, strongly depleted, but nevertheless highly supersaturated ($S\!\gg\!1$). These particles settle gravitationally and populate the warmer layers below, where the in-situ formation (nucleation) is ineffective or even not possible. During their descent, the particles grow up to radii $\approx\!0.3\,\mu{\rm m}\,...\,150\,\mu{\rm m}$, depending gas around the cloud base. The particles finally sink into layers which are sufficiently hot to cause their thermal evaporation. Hence, an effective transport mechanism for condensable elements exi considered solid/liquid material. In the stationary case studied here, this downward directed element transport by precipitating dust grains is balanced by an upward directed flux of condensable elements from the deep interior of the star via convective mixing (no dust without mixing). We find a self-regulation mechanism which leads to an approximate phase equilibrium ($S\!\approx\!1$) around the cloud base. The mass fraction of dust present in the atmosphere results be to approximately given by the mass fraction of condensable elements in the gas being mixed up.
    Keywords: ddc:000
    Language: English
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  • 5
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    Visualization of Time-Dependent Adaptive Mesh Refinement Data (2003)
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    Publication Date: 2020-03-09
    Description: Analysis of phenomena that simultaneously occur on quite different spatial and temporal scales require adaptive, hierarchical schemes to reduce computational and storage demands. For data represented as grid functions, the key are adaptive, hierarchical, time-dependent grids that resolve spatio-temporal details without too much redundancy. Here, so-called AMR grids gain increasing popularity. For visualization and feature identification/tracking, the underlying continuous function has to be faithfully reconstructed by spatial and temporal interpolation. Well designed interpolation methods yield better results and help to reduce the amount of data to be stored. We address the problem of temporal interpolation of AMR grid data, e.g.\ for creation of smooth animations or feature tracking. Intermediate grid hierarchies are generated by merging the cells on all refinement levels that are present in the key frames considered. Utilizing a clustering algorithm a structure of nested grids is induced on the resulting collection of cells. The grid functions are mapped to the intermediate hierarchy, thus allowing application of appropriate interpolation techniques.
    Keywords: ddc:000
    Language: English
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  • 6
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    Tensor Splats (2003)
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    Publication Date: 2020-03-09
    Description: An improved general-purpose technique for the visualization of symmetric positive definite tensor fields of rank two is described. It is based on a splatting technique that is built from tiny transparent glyph primitives which are capable to incorporate the full directional information content of a tensor. The result is an information-rich image that allows to read off the preferred directions in a tensor field at each point of a three-dimensional volume or two-dimensional surface. It is useful for analyzing slices or volumes of a three-dimensional tensor field and can be overlayed with standard volume rendering or color mapping. The application of the rendering technique is demonstrated on general relativistic data and the diffusion tensor field of a human brain.
    Keywords: ddc:000
    Language: English
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  • 7
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    A construction for non-rank facets of stable set polytopes of webs (2003)
    Details
    Publication Date: 2014-11-10
    Description: Graphs with circular symmetry, called webs, are relevant for describing the stable set polytopes of two larger graph classes, quasi-line graphs [{\sl Giles and Trotter 1981, Oriolo 2001}] and claw-free graphs [{\sl Galluccio and Sassano 1997, Giles and Trotter 1981}]. Providing a decent linear description of the stable set polytopes of claw-free graphs is a long-standing problem [{\sl Grötschel, Lov\'asz, and Schrijver 1988}]. However, even the problem of finding all facets of stable set polytopes of webs is open. So far, it is only known that stable set polytopes of webs with clique number $\leq 3$ have rank facets only [{\sl Dahl 1999, Trotter 1975}] while there are examples with clique number $\geq 4$ having non-rank facets [{\sl e.g. Liebling et al. 2003, Oriolo 2001, P\^echer and Wagler 2003}]. In this paper, we provide a construction for non-rank facets of stable set polytopes of webs. We use this construction to prove, for several fixed values of $\omega$ including all odd values at least 5, that there are only finitely many webs with clique number $\omega$ whose stable set polytopes admit rank facets only.
    Keywords: ddc:000
    Language: English
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  • 8
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    Automatic Construction of Boundary Parametrizations for Geometric Multigrid Solvers (2003)
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    Publication Date: 2020-11-13
    Description: We present an algorithm that constructs parametrizations of boundary and interface surfaces automatically. Starting with high-resolution triangulated surfaces describing the computational domains, we iteratively simplify the surfaces yielding a coarse approximation of the boundaries with the same topological type. While simplifying we construct a function that is defined on the coarse surface and whose image is the original surface. This function allows access to the correct shape and surface normals of the original surface as well as to any kind of data defined on it. Such information can be used by geometric multigrid solvers doing adaptive mesh refinement. Our algorithm runs stable on all types of input surfaces, including those that describe domains consisting of several materials. We have used our method with success in different fields and we discuss examples from structural mechanics and biomechanics.
    Keywords: ddc:000
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  • 9
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    Combinatorial Packing Problems (2003)
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    Publication Date: 2020-08-05
    Description: This article investigates a certain class of combinatorial packing problems and some polyhedral relations between such problems and the set packing problem.
    Keywords: ddc:000
    Language: English
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  • 10
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    Small Examples of Non-Constructible Simplicial Balls and Spheres (2003)
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    Publication Date: 2014-02-26
    Description: We construct non-constructible simplicial $d$-spheres with $d+10$ vertices and non-constructible, non-realizable simplicial $d$-balls with $d+9$ vertices for $d\geq 3$.
    Keywords: ddc:000
    Language: English
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  • 11
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    A Lagrangian Approach for Integrated Network Design and Routing in IP Networks (2003)
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    Publication Date: 2014-11-11
    Description: We consider the problem of designing a network that employs a non-bifurcated shortest path routing protocol. The network's nodes and the set of potential links are given together with a set of forecasted end-to-end traffic demands. All relevant hardware components installable at links or nodes are considered. The goal is to simultaneously choose the network's topology, to decide which hardware components to install on which links and nodes, and to find appropriate routing weights such that the overall network cost is minimized. In this paper, we present a mathematical optimization model for this problem and an algorithmic solution approach based on a Lagrangian relaxation. Computational results achieved with this approach for several real-world network planning problems are reported.
    Keywords: ddc:000
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  • 12
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    Comparing Restoration Concepts using Optimal Network Configurations with Integrated Hardware and Routing Decisions (2003)
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    Publication Date: 2014-02-26
    Description: We investigate the impact of link and path restoration on the cost of telecommunication networks. The surprising result is the following: the cost of an optimal network configuration is almost independent of the restoration concept if (i) the installation of network elements (ADMs, DXCs, or routers) and interface cards, (ii) link capacities, and (iii) working and restoration routings are simultaneously optimized. We present a mixed-integer programming model which integrates all these decisions. Using a branch-and-cut algorithm (with column generation to deal with all potential routing paths), we solve structurally different real-world problem instances and show that the cost of optimal solutions is almost independent of the used restoration concept. In addition, we optimize spare capacities for given shortest working paths which are predetermined with respect to different link metrics. In comparison to simultaneous optimization of working and restoration routings, it turns out that this approach does not allow to obtain predictably good results.
    Keywords: ddc:000
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  • 13
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    Average Case Analysis of a Hard Dial-a-Ride Problem (2003)
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    Publication Date: 2020-11-13
    Description: In the dial-a-ride-problem (DARP) objects have to be moved between given sources and destinations in a transportation network by means of a server. The goal is to find a shortest transportation for the server. We study the DARP when the underlying transportation network forms a caterpillar. This special case is strongly NP-hard in the worst case. We prove that in a probabilistic setting there exists a polynomial time algorithm which almost surely finds an optimal solution. Moreover, with high probability the optimality of the solution found can be certified efficiently. We also examine the complexity of the DARP in a semi-random setting and in the unweighted case.
    Keywords: ddc:000
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  • 14
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    Asymptotic Mesh Independence of Newton's Method Revisited (2003)
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    Publication Date: 2019-01-29
    Description: The paper presents a new affine invariant theory on asymptotic mesh independence of Newton's method in nonlinear PDEs. Compared to earlier attempts, the new approach is both much simpler and more natural from the algorithmic point of view. The theory is exemplified at collocation methods for ODE boundary value problems and at finite element methods for elliptic PDE problems.
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  • 15
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    Smoothening Helps: A Probabilistic Analysis of the Multi-Level Feedback Algorithm (2003)
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    Publication Date: 2014-02-26
    Description: In this paper we introduce the notion of smoothed competitive analysis of online algorithms. Smoothed analysis has been proposed by [{\sl Spielman and Teng} STOC 2001] to explain the behaviour of algorithms that work well in practice while performing very poorly from a worst case analysis point of view. We apply this notion to analyze the Multi-Level Feedback (MLF) algorithm to minimize the total flow time on a sequence of jobs released over time when the processing time of a job is only known at time of completion. The initial processing times are integers in the range $[1,2^K]$. We use a partial bit randomization model, where the initial processing times are smoothened by changing the $k$ least significant bits under a quite general class of probability distributions. We show that MLF admits a smoothed competitive ratio of $O(max((2^k/\sigma)^3, (2^k/\sigma)^2 2^K-k))$, where $\sigma$ denotes the standard deviation of the distribution. In particular, we obtain a competitive ratio of $O(2^K-k)$ if $\sigma = \Theta(2^k)$. %The analysis holds for an oblivious as well as for a stronger adaptive %adversary. We also prove an $\Omega(2^{K-k})$ lower bound for any deterministic algorithm that is run on processing times smoothened according to the partial bit randomization model. For various other smoothening models, including the additive symmetric smoothening model used by [{\sl Spielman and Teng}], we give a higher lower bound of $\Omega(2^K)$. A direct consequence of our result is also the first average case analysis of MLF. We show a constant expected ratio of the total flow time of MLF to the optimum under several distributions including the uniform distribution.
    Keywords: ddc:000
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  • 16
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    A sample path relation for the sojourn times in G/G/1-PS systems and its applications (2003)
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    Publication Date: 2014-11-11
    Description: For the general G/G/1 processor sharing (PS) system a sample path result for the sojourn times in a busy period is proved, which yields a relation between the sojourn times under PS and FCFS discipline. In particular, the result provides a formula for the mean sojourn time in G/D/1-PS in terms of the mean sojourn time in the corresponding G/D/1-FCFS, generalizing known results for GI/M/1 and M/GI/1. Extensions of the formula provide the basis for a two-moment approximation of the mean sojourn time in G/GI/1-PS in terms of a related G/D/1-FCFS.
    Keywords: ddc:000
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  • 17
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    Molecular Conformation Dynamics and Computational Drug Design (2003)
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    Publication Date: 2014-02-26
    Description: The paper surveys recent progress in the mathematical modelling and simulation of essential molecular dynamics. Particular emphasis is put on computational drug design wherein time scales of $msec$ up to $min$ play the dominant role. Classical long-term molecular dynamics computations, however, would run into ill-conditioned initial value problems already after time spans of only $psec=10^{-12} sec$. Therefore, in order to obtain results for times of pharmaceutical interest, a combined deterministic-stochastic model is needed. The concept advocated in this paper is the direct identification of metastable conformations together with their life times and their transition patterns. It can be interpreted as a {\em transfer operator} approach corresponding to some underlying hybrid Monte Carlo process, wherein short-term trajectories enter. Once this operator has been discretized, which is a hard problem of its own, a stochastic matrix arises. This matrix is then treated by {\em Perron cluster analysis}, a recently developed cluster analysis method involving the numerical solution of an eigenproblem for a Perron cluster of eigenvalues. In order to avoid the 'curse of dimension', the construction of appropriate boxes for the spatial discretization of the Markov operator requires careful consideration. As a biomolecular example we present a rather recent SARS protease inhibitor.
    Keywords: ddc:000
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  • 18
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    Nonlinear Optimization in Gas Networks (2003)
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    Publication Date: 2021-02-01
    Description: The operative planning problem in natural gas distribution networks is addressed. An optimization model focusing on the governing PDE and other nonlinear aspects is presented together with a suitable discretization for transient optimization in large networks by SQP methods. Computational results for a range of related dynamic test problems demonstrate the viability of the approach.
    Keywords: ddc:000
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  • 19
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    RNA 3D-Modeling (2003)
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    Publication Date: 2014-02-26
    Description: This article presents a new computational approach to the three-dimensional (3D) modeling of ribonucleic acid (RNA) sequences with unknown spatial structure. The main concept is a mapping of the query sequence onto the 3D structures of a suitable template RNA molecule. This technique called \textit{threading} has originally been developed for the modeling of protein 3D structures. The application to RNA systems bridges the information gap between the growing mass of RNA sequence data and the relatively limited number of available 3D structures. The new RNA threading method is demonstrated on a tRNA model system because sufficient representative 3D structures have experimentally been elucidated and deposited in the public databases. Nevertheless, the method is in principle transferable on all other RNA species. Algorithms are developed that decompose these template structures into their secondary structure elements and gather this information in a specific template database. The best template is chosen with public alignment and secondary structure prediction tools which are integrated in the RNA modeling module. The structural information gathered from the template and the best alignment is combined to establish a comprehensive 3D model of the query sequence. A range of complete tRNA structures has successfully been modeled with the RNA threading method. The prototype module visualizes the models and provides convenient access to the proposed 3D structures. Therefore, the method could give new insight into a variety of RNA systems which in the recent years have become increasingly important as potential new pharmaceutical agents.
    Keywords: ddc:000
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  • 20
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    Korean-German Bilateral Symposium on Scientific Computing (2003)
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    Publication Date: 2014-02-26
    Description: Collection of abstracts of the Korean-German Bilateral Symposium on Scientific Computing, Berlin January 15/16, 2004
    Keywords: ddc:000
    Language: English
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  • 21
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    Planung kostenoptimaler Informations- und Kommunikations-Infrastrukturen (2003)
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    Publication Date: 2014-11-11
    Description: Beim Entwurf und Ausbau von Informations- und Kommunikationsnetzwerken m{ü}ssen zahlreiche interdependente Entscheidungen getroffen und gleichzeitig mannigfaltige Bedingungen ber{ü}cksichtigt werden. Die verf{ü}gbaren technischen und organisatorischen Alternativm{ö}glichkeiten sind normalerweise so vielf{ä}ltig und komplex, dass eine manuelle Planung praktisch nicht m{ö}glich ist. In diesem Artikel wird das Potential und die Methodik der mathematischen Optimierung bei der kostenoptimalen Planung von Kommunikationsnetzen vorgestellt. Als Ausgangspunkt wird exemplarisch eine typische praktische Aufgabe, die Struktur- und Konfigurationsplanung mehrstufiger Telekommunikationsnetzwerke, dargestellt. Anschließend werden kurz die wesentlichen Modellierungstechniken und Verfahrensans{ä}tze der mathematischen Optimierung skizziert. Abschließend gehen wir auf die Planung einer ad{ä}quaten Informations- und Kommunikations- Infrastruktur f{ü}r ein dezentrales Energieversorgungsnetz ein.
    Keywords: ddc:000
    Language: German
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  • 22
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    Chromatic Scheduling Polytopes coming from the Bandwidth Allocation Problem in Point-to-Multipoint Radio AccessSystems (2003)
    Details
    Publication Date: 2020-08-05
    Description: Point-to-Multipoint systems are one kind of radio systems supplying wireless access to voice/data communication networks. Such systems have to be run using a certain frequency spectrum, which typically causes capacity problems. Hence it is, on the one hand, necessary to reuse frequencies but, on the other hand, no interference must be caused thereby. This leads to the bandwidth allocation problem, a special case of so-called chromatic scheduling problems. Both problems are NP-hard, and there exist no polynomial time approximation algorithms with a guaranteed quality. One kind of algorithms which turned out to be successful for many other combinatorial optimization problems uses cutting plane methods. In order to apply such methods, knowledge on the associated polytopes is required. The present paper contributes to this issue, exploring basic properties of chromatic scheduling polytopes and several classes of facet-defining inequalities.
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  • 23
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    Optimization Methods for UMTS Radio Network Planning (2003)
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    Publication Date: 2020-02-11
    Description: The UMTS radio network planning problem poses the challenge of designing a cost-effective network that provides users with sufficient coverage and capacity. We describe an optimization model for this problem that is based on comprehensive planning data of the EU project MOMENTUM. We present heuristic mathematical methods for this realistic model, including computational results.
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  • 24
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    Assessing Capacity Improvements by Relaying in Cellular Networks (2003)
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    Publication Date: 2014-02-26
    Description: Relaying -- allowing multiple wireless hops -- is a protocol extension for cellular networks conceived to improve data throughput. Its benefits have only been quantified for small example networks. For assessing its general potential, we define a complex resource allocation\slash{}scheduling problem. Several mathematical models are presented for this problem; while a time-expanded MIP approach turns out intractable, a sophisticated column generation scheme leads to good computational results. We thereby show that for selected cases relaying can increase data throughput by 30\% on the average.
    Keywords: ddc:000
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  • 25
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    Minimum Converter Wavelength Assignment in All-Optical Networks (2003)
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    Publication Date: 2014-02-26
    Description: Finding conflict-free wavelength assignments with a minimum number of required conversions for a routing of the lightpaths is one of the important tasks within the design of all-optical networks. We consider this problem in multi-fiber networks with different types of WDM systems. We give a detailed description of the problem and derive its theoretical complexity. For practical application, we propose several sequential algorithms to compute appropriate wavelength assignments. We also perform computational experiments to evaluate their performance. For the iterative algorithms, we identify characteristic patterns of progression. Two of these algorithms qualify for application in practice.
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  • 26
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    Rigid body docking for Virtual Screening (2003)
    Details
    Publication Date: 2014-09-30
    Description: A recently developed algorithm allows Rigid Body Docking of ligands to proteins, regardless of the accessibility and location of the binding site. The Docking procedure is divided into three subsequent optimization phases, two of which utilize rigid body dynamics. The last one is applied with the ligand already positioned inside the binding pocket and accounts for full flexibility. Initially, a combination of geometrical and force-field based methods is used as a Coarse Docking strategy, considering only Lennard-Jones interactions between the target and pharmaceutically relevant atoms or functional groups. The protein is subjected to a Hot Spot Analysis, which reveals points of high affinity in the protein environment towards these groups. The hot spots are distributed into different subsets according to their group affiliation. The ligand is described as a complementary point set, consisting of the same subsets. Both sets are matched in $\mathrm{I\!R}^{3}$, by superimposing members of the same subsets. In the first instance, steric inhibition is nearly neglected, preventing the system's trajectory from trapping in local minima and thus from finding false positive solutions. Hence the exact location of the binding site can be determined fast and reliably without any additional information. Subsequently, errors resulting from approximations are minimized via finetuning, this time considering both Lennard-Jones and Coulomb forces. Finally, the potential energy of the whole complex is minimized. In a first evaluation, results are rated by a reduced scoring function considering only noncovalent interaction energies. Exemplary Screening results will be given for specific ligands.
    Keywords: ddc:000
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    Integrated Optimization of Hardware Configuration and Capacity. Dimensioning in SDH and opaque WDM networks (2003)
    Details
    Publication Date: 2014-02-26
    Description: We suggest a new model for the design of telecommunication networks which integrates decisions about the topology, configuration of the switching hardware, link dimensioning, and protected routing of communication demands. Applying the branch-and-cut-algorithm implemented in our network planning and optimization tool DISCNET, we demonstrate that real-world based network planning instances of such an enhanced model can be solved.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Verteilter Dokumenten-Speicher, Erfahrungen mit den Kluwer-Daten des Friedrich-Althoff-Konsortiums (2003)
    Details
    Publication Date: 2020-02-11
    Description: Dieser Bericht beschreibt die Erfahrungen und Schlussfolgerungen,die im Rahmen der VDS-Vorstudie bei der Speicherung der vom Friedrich-Althoff-Konsortium lizenzierten Zeitschriften des Kluwer-Verlages gewonnen wurden.
    Keywords: ddc:000
    Language: German
    Type: reportzib , doc-type:preprint
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    Endnutzerbasierte Online-Fernleihe im KOBV - Kurzbeschreibung (2003)
    Details
    Publication Date: 2020-11-13
    Description: Der KOBV setzt für die endnutzerbasierte Online-Fernleihe den Sisis ZFL-Server (Zentraler Fernleih-Server) ein. Mit dem Einsatz des ZFL-Servers können in den Bibliotheken echte Rationalisierungseffekte erzielt werden: Der Server ist in der Lage, Fernleih-Bestellungen an lokale Systeme zu übergeben, so dass sie im lokalen System automatisch - ohne Eingreifen von Bibliotheksmitarbeitern - weiterverarbeitet werden können. Im KOBV können derzeit Sisis- und Aleph-Lokalsysteme diese Schnittstelle voll bedienen. Andere Bibliothekssysteme im KOBV, die diese Schnittstelle nicht bedienen können, werden mittels eines E-Mail-Verfahrens in die Online-Fernleihe integriert. Die vorliegende Kurzbeschreibung der Online-Fernleihe im KOBV soll - im Gegensatz zur Spezifikation, die möglichst vollständig sein sollte - einen leicht verständlichen Einblick in die Abläufe der Online-Fernleihe vermitteln. Nach einem Überblick über zu erwartende Rationalisierungseffekte ist der Ablauf einer Online-Fernleih-Bestellung - veranschaulicht durch eine Graphik mit dem technischen Aufbau im KOBV - kurz dargestellt. \vspace{6mm} {\it Hinweis:} Die von einer Arbeitsgruppe des KOBV erstellte Spezifikation zur Online-Fernleihe ist als ZIB Report 02-30 auf dem Preprint-Server des ZIB veröffentlicht. Siehe: Monika Kuberek (Red.) {\begin{rawhtml} 〈a href="http://www.zib.de/Publications/Reports/ZR-02-30.pdf"〉 〈i〉 Spezifikation für eine Verbund-Fernleih-Software im KOBV〈/i〉 〈/a〉 \end{rawhtml}}
    Keywords: ddc:000
    Language: German
    Type: reportzib , doc-type:preprint
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    Improved Perron Cluster Analysis (2003)
    Details
    Publication Date: 2014-02-26
    Description: The problem of clustering data can often be transformed into the problem of finding a hidden block diagonal structure in a stochastic matrix. Deuflhard et al. have proposed an algorithm that state s the number $k$ of clusters and uses the sign structure of $k$ eigenvectors of the stochastic matrix to solve the cluster problem. Recently Weber and Galliat discovered that this system of eigenvectors can easily be transformed into a system of $k$ membership functions or soft characteristic functions describing the clusters. In this article we explain the corresponding cluster algorithm and point out the underlying theory. By means of numerical examples we explain how the grade of membership can be interpreted.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Zur Zugriffskontrolle im KOBV (2003)
    Details
    Publication Date: 2014-02-26
    Description: Mit der Entwicklung des KOBV-Informationsportals soll den Benutzern in der Region Berlin-Brandenburg ein verbesserter Zugang zu Informationsressourcen geboten werden. Einen wesentlichen Anteil diese Auf der Grundlage der Analyse der Rahmenbedingungen werden Anforderungen an die Zugriffskontrolle im KOBV definiert und Lösungsmöglichkeiten auf der Ebene allgemeiner Modelle diskutiert.
    Keywords: ddc:000
    Language: German
    Type: reportzib , doc-type:preprint
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    Navigation in the KOBV-Informationsportal Conceptual View (2003)
    Details
    Publication Date: 2014-02-26
    Description: The KOBV Informationsportal aims to be a universal gateway to the sources of information hosted by the partner libraries from the Berlin-Brandenburg area. Due to the large number of these sources, an intuitive navigation is an essential component of the portal. The navigation-component should preserve the partner libraries? independence and overcome their administrative and technical differences. This paper proposes a collection-level navigation with four dimensions: the sources? subject areas (e.g. the first two levels of DDC), the sources? type (e.g. e-journals, databases, OPACs, etc.), the sources? location (e.g. Berlin, Brandenburg) / the library that hosts that source and the sources? accessing state (e.g. free, restricted, etc.).
    Keywords: ddc:000
    Language: English
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    Polynomial Inequalities Representing Polyhedra (2003)
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    Publication Date: 2014-02-26
    Description: Our main result is that every n-dimensional polytope can be described by at most (2n-1) polynomial inequalities and, moreover, these polynomials can explicitly be constructed. For an n-dimensional pointed polyhedral cone we prove the bound 2n-2 and for arbitrary polyhedra we get a constructible representation by 2n polynomial inequalities.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    The final NETLIB-LP results (2003)
    Details
    Publication Date: 2020-02-11
    Description: The NETLIB has now served for 18 years as a repository of LP problem instances. From the beginning to the present day there was some uncertainness about the precise values of the optimal solutions. We implemented a program using exact rational arithmetic to compute proofs for the feasibility and optimality of an LP solution. This paper reports the \emph{exact} optimal objective values for all NETLIB problems.
    Keywords: ddc:000
    Language: English
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    Dust formation in brown dwarf atmospheres under conditions of driven turbulence (2003)
    Details
    Publication Date: 2014-02-26
    Description: Based on the knowledge gained from direct numerical simulations which are only possible in the microscale regime, a concept of driven turbulence is presented which allows to enter the mesoscopic scale regime. Here, dust formation under stochastic hydro- and thermodynamic conditions is studied: constructively superimposed stochastic waves initiate dust formation by the creation of singular nucleation events. It, hence, results a varying mean grain size and dust density in space and time. The newly formed dust changes the thermodynamic behavior from almost isotherm to adiabatic and chemically depletes the gas phase.
    Keywords: ddc:000
    Language: English
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    Kosten- und Qualitätsoptimierung in Kommunikationsnetzen (2003)
    Details
    Publication Date: 2014-11-11
    Description: Der scharfe Wettbewerb innerhalb der Telekommunikationsbranche zwingt die Netzbetreiber dazu, ihre Investitionen genau zu planen und immer wieder Einsparungsmanahmen durchzuführen. Gleichzeitig ist es jedoch wichtig, die Qualität der angebotenen Dienste zu verbessern, um neue Kunden zu gewinnen und langfristig an sich zu binden. Die mathematische Optimierung bietet sich für viele solcher Aufgabenstellungen als hervorragend geeignetes Planungswerkzeug an. Ziel dieses Artikels ist es, ihre Methodik und ihre Anwendung speziell zur Kosten- und Qualitätsoptimierung in Kommunikationsnetzen vorzustellen. Anhand von vier konkreten Planungsaufgaben aus dem Bereich der Festnetzplanung wird aufgezeigt, wie sich komplexe Zusammenhänge in flexiblen mathematischen Modellen abbilden lassen und welche Verfahren zur automatisierten Bearbeitung der Probleme eingesetzt werden können. Die hier vorgestellten Methoden zeichnen sich insbesondere dadurch aus, dass sie neben hochwertigen Lösungen auch eine Qualittsgarantie liefern, mit der sich die Lsungen fundiert bewerten lassen. Die dokumentierten Ergebnisse aus verschiedenen Industrieprojekten belegen die Eignung und Güte der mathematischen Optimierung für die Praxis.
    Keywords: ddc:000
    Language: German
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    Dust in Brown Dwarfs IV. Dust formation and driven turbulence on mesoscopic scales (2003)
    Details
    Publication Date: 2014-02-26
    Description: Dust formation {in brown dwarf atmospheres} is studied by utilizing a model for driven turbulence in the mesoscopic scale regime. We apply a pseudo-spectral method where waves are created and superimposed {within} a {limited} wavenumber interval. The turbulent kinetic energy distribution follows the Kolmogoroff spectrum which is assumed to be the most likely value. Such superimposed, stochastic waves may occur in a convectively active environment. They cause nucleation fronts and nucleation events and thereby initiate the dust formation process which { continues until} all condensible material is consumed. Small disturbances {are found to} have a large impact on the dust forming system. An initially dust-hostile region, which may originally be optically thin, becomes optically thick in a patchy way showing considerable variations in the dust properties during the formation process. The dust appears in lanes and curls as a result of the interaction with waves, i.e. turbulence, which form larger and larger structures with time. Aiming on a physical understanding of the variability of brown dwarfs, related to structure formation in substellar atmospheres, we work out first necessary criteria for small-scale closure models to be applied in macroscopic simulations of dust forming astrophysical systems.
    Keywords: ddc:000
    Language: English
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    The multi-scale dust formation in substellar atmospheres (2003)
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    Publication Date: 2014-02-26
    Description: Substellar atmospheres are observed to be irregularly variable for which the formation of dust clouds is the most promising candidate explanation. The atmospheric gas is convectively unstable and, last but not least, colliding convective cells are seen as cause for a turbulent fluid field. Since dust formation depends on the local properties of the fluid, turbulence influences the dust formation process and may even allow the dust formation in an initially dust-hostile gas. A regime-wise investigation of dust forming substellar atmospheric situations reveals that the largest scales are determined by the interplay between gravitational settling and convective replenishment which results in a dust-stratified atmosphere. The regime of small scales is determined by the interaction of turbulent fluctuations. Resulting lane-like and curled dust distributions combine to larger and larger structures. We compile necessary criteria for a subgrid model in the frame of large scale simulations as result of our study on small scale turbulence in dust forming gases.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    HelmPole - A finite element solver for scattering problems on unbounded domains: Implementation based on PML (2003)
    Details
    Publication Date: 2019-01-24
    Description: The solution of scattering problems described by the Helmholtz equation on unbounded domains is of importance for a wide variety of applications, for example in electromagnetics and acoustics. An implementation of a solver for scattering problems based on the programming language Matlab is introduced. The solver relies on the finite-element-method and on the perfectly-matched-layer-method, which allows for the simulation of scattering problems on complex geometries surrounded by inhomogeneous exterior domains. This report gives a number of detailed examples and can be understood as a user manual to the freely accessible code of the solver HelmPole.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Progressive Retrieval and Hierarchical Visualization of Large Remote Data (2003)
    Details
    Publication Date: 2020-03-09
    Description: \noindent The size of data sets produced on remote supercomputer facilities frequently exceeds the processing capabilities of local visualization workstations. This phenomenon increasingly limits scientists when analyzing results of large-scale scientific simulations. That problem gets even more prominent in scientific collaborations, spanning large virtual organizations, working on common shared sets of data distributed in Grid environments. In the visualization community, this problem is addressed by distributing the visualization pipeline. In particular, early stages of the pipeline are executed on resources closer to the initial (remote) locations of the data sets. \noindent This paper presents an efficient technique for placing the first two stages of the visualization pipeline (data access and data filter) onto remote resources. This is realized by exploiting the ``extended retrieve'' feature of GridFTP for flexible, high performance access to very large HDF5 files. We reduce the number of network transactions for filtering operations by utilizing a server side data processing plugin, and hence reduce latency overhead compared to GridFTP partial file access. The paper further describes the application of hierarchical rendering techniques on remote uniform data sets, which make use of the remote data filtering stage.
    Keywords: ddc:000
    Language: English
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    The Potential of Relaying in Cellular Networks (2003)
    Details
    Publication Date: 2014-02-26
    Description: Relaying is a protocol extension for cellular wireless computer networks; in order to utilize radio resources more efficiently, several hops are allowed within one cell. This paper investigates the principle potential of relaying by casting transmission scheduling as a mathematical optimization problem, namely, a linear program. We analyze the throughput gains showing that, irrespective of the concrete scheduling algorithm, performance gains of up to 30\% on average for concrete example networks are achievable.
    Keywords: ddc:000
    Language: English
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    Critical and Anticritical Edges with respect to Perfectness (2003)
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    Publication Date: 2014-02-26
    Description: We call an edge $e$ of a perfect graph $G$ critical if $G-e$ is imperfect and call $e$ anticritical if $G+e$ is imperfect. The present paper surveys several questions in this context. We ask in which perfect graphs critical and anticritical edges occur and how to detect such edges. The main result by [{\sl Wagler, PhD thesis 2000}] shows that a graph does not admit any critical edge if and only if it is Meyniel. The goal is to order the edges resp.~non-edges of certain perfect graphs s.t. deleting resp.~adding all edges in this order yields a sequence of perfect graphs only. Results of [{\sl Hayward 1985}] and [{\sl Spinrad & Sritharan 1995}] show the existence of such edge orders for weakly triangulated graphs; the line-perfect graphs are precisely these graphs where all edge orders are perfect [{\sl Wagler 2001}]. Such edge orders cannot exist for every subclass of perfect graphs that contains critically resp.~anticritically perfect graphs where deleting resp.~adding an arbitrary edge yields an imperfect graph. We present several examples and properties of such graphs, discuss constructions and characterizations from [{\sl Wagler 1999, Wagler PhD thesis 2000}]. An application of the concept of critically and anticritically perfect graphs is a result due to [{\sl Hougardy & Wagler 2002}] showing that perfectness is an elusive graph property.
    Keywords: ddc:000
    Language: English
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    Accelerating Hasenbusch's Acceleration of Hybrid Monte Carlo (2003)
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    Publication Date: 2014-02-26
    Description: Hasenbusch has proposed splitting the pseudo-fermionic action into two parts, in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a different splitting, also using clover-improved Wilson fermions. An additional speed-up between 5 and 20\% over the original proposal was achieved in production runs.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Safe separators for treewidth (2003)
    Details
    Publication Date: 2014-11-10
    Description: A set of vertices $S\subseteq V$ is called a safe separator for treewidth, if $S$ is a separator of $G$, and the treewidth of $G$ equals the maximum of the treewidth over all connected components $W$ of $G-S$ of the graph, obtained by making $S$ a clique in the subgraph of $G$, induced by $W\cup S$. We show that such safe separators are a very powerful tool for preprocessing graphs when we want to compute their treewidth. We give several sufficient conditions for separators to be safe, allowing such separators, if existing, to be found in polynomial time. In particular, every minimal separator of size one or two is safe, every minimal separator of size three that does not split off a component with only one vertex is safe, and every minimal separator that is an almost clique is safe; an almost clique is a set of vertices $W$ such that there is a $v\in W$ with $W-\{v\}$ a clique. We report on experiments that show significant reductions of instance sizes for graphs from proba! bilistic networks and frequency assignment.
    Keywords: ddc:000
    Language: English
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    Interior Point Methods in Function Space (2003)
    Details
    Publication Date: 2019-01-29
    Description: A primal-dual interior point method for optimal control problems is considered. The algorithm is directly applied to the infinite dimensional problem. Existence and convergence of the central path are analyzed, and linear convergence of a short step pathfollowing method is established.
    Keywords: ddc:000
    Language: English
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    Triangulated Manifolds with Few Vertices: Geometric 3-Manifolds (2003)
    Details
    Publication Date: 2014-02-26
    Description: We explicitly construct small triangulations for a number of well-known $3$-dimensional manifolds and give a brief outline of some aspects of the underlying theory of $3$-manifolds and its historical development.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Lastbalancierung in Peer-to-Peer Systemen (2003)
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    Publication Date: 2016-06-30
    Description: Peer-to-Peer (P2P) Systeme werden u.a. zur Verwaltung von großen Datenmengen benutzt, die auf verschiedene Rechner verteilt sind. Benutzern soll damit der Zugriff auf Daten innerhalb des Systems leicht ermöglicht werden. Damit in P2P Systemen die Daten effizient verteilt und gesucht werden können, existieren Distributed Hash Tables. Distributed Hash Tables (DHT) sind eine Methode, um globale Informationen persistent speichern zu können. Der Wertebereich der Hashfunktion, welche die zu veröffentlichenden Einträge auf Werte abbildet, wird in Abschnitte aufgeteilt, die einzelnen Knoten zugeteilt werden. Die meisten DHTs haben aber ein Problem bei der Verteilung der Last. Die verschiedenen DHT Systeme beruhen meist auf einem identischen Ansatz der Lastverteilung. Die Last wird nur mit Hilfe einer Hashfunktion verteilt. Es wird davon ausgegangen, dass diese Funktion die Last gleichmäßig verteilt. Im Rahmen dieser Arbeit wurde ein Verfahren zur Last Verteilung entwickelt, simuliert und implementiert. Bei dem Verfahren wird die Last wie bei der Verteilung von Wärme an die Umgebung abgegeben. Es wird mit existierenden Lastbalancierungsalgorithmen verglichen. Mit diesem neuen Verfahren ist es möglich, Last in DHTs besser zu verteilen ohne große Änderungen an den DHTs vorzunehmen. Es wird gezeigt, wie mit dem Verfahren zusätzlich die Fehlertoleranz des P2P Systems erhöht werden kann.
    Description: One of the many uses of Peer-to-Peer (P2P) systems is the administration of large data sets that are distributed across different computers, with the goal of facilitating user access to files within the system. Distributed Hash Tables (DHT) are designed to enable the efficient distribution and search of files, by allowing global information to be persistently stored. The range of values of the hash function (the possible entries in the published hash table) are assigned to individual nodes. Most DHTs, however, have a problem with load distribution. The various DHT systems usually operate by distributing load equally among nodes. Thus the load is distributed using the help of the hash function. One assumes this function distributes the load evenly. In the context of this work a method of distributing load has been developed, simulated and implemented. With this method load is transferred in a fashion analogous to the dissipation of heat into the environment. Comparisons with existing algorithms for load balancing are drawn. With the new procedure it is possible to better distribute load in DHTs without requiring major changes to the DHTs themselves. It is shown that with the procedure the fault tolerance of P2P systems may also be increased.
    Keywords: ddc:000
    Language: German
    Type: masterthesis , doc-type:masterThesis
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    Robust Perron Cluster Analysis in Conformation Dynamics (2003)
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    Publication Date: 2014-02-26
    Description: The key to molecular conformation dynamics is the direct identification of metastable conformations, which are almost invariant sets of molecular dynamical systems. Once some reversible Markov operator has been discretized, a generalized symmetric stochastic matrix arises. This matrix can be treated by Perron cluster analysis, a rather recent method involving a Perron cluster eigenproblem. The paper presents an improved Perron cluster analysis algorithm, which is more robust than earlier suggestions. Numerical examples are included.
    Keywords: ddc:000
    Language: English
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    Demand-wise Shared Protection for Meshed Optical Networks (2003)
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    Publication Date: 2014-11-11
    Description: In this paper, a new shared protection mechanism for meshed optical networks is presented. Significant network design cost reductions can be achieved in comparison to the well-known 1+1 protection scheme. Demand-wise Shared Protection (DSP) bases on the diversification of demand routings and exploits the network connectivity to restrict the number of backup lightpaths needed to provide the desired level of prorection. Computational experiments approve the benefits of the concept DSP for cost efficient optical network designs.
    Keywords: ddc:000
    Language: English
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    Simulation of the Human Mandible: Comparison of Bone Mineral Density and Stress/Strain Profiles due to Masticatory Muscles' Traction (2003)
    Details
    Publication Date: 2019-05-10
    Description: The correlation of the inner architecture of bone and its functional loading was already stated by Wolff in 1892. Our objective is to demonstrate this interdependence in the case of the human mandible. For this purpose, stress/strain profiles occuring at a human lateral bite were simulated. Additionally, by a combination of computer graphics modules, a three--dimensional volumetric visualization of bone mineral density could be given. Qualitative correspondences between the density profile of the jaw and the simulated stress/strain profiles could be pointed out. In the long run, this might enable the use of the simulation for diagnosis and prognosis. The solution of the underlying partial differential equations describing linear elastic material behaviour was provided by an adaptive finite element method. Estimates of the discretization errors, local grid refinement, and multilevel techniques guaranteed the reliability and efficiency of the method.
    Keywords: ddc:000
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    MoDySim - A parallel dynamical UMTS simulator (2003)
    Details
    Publication Date: 2014-02-26
    Description: UMTS is a 3rd generation mobile telecommunication system which enables multi-service and multi-bit rate communication going beyond the possibilities of previous systems. The simulator MoDySim models UMTS in great detail. Characteristics of UMTS such as soft hand-over and the interdependency of load and capacity among neighbouring cells are challenges for the parallelisation of such a system. In this paper we explain how the software was parallelised and present performance results of a UMTS simulation for the city of Berlin.
    Keywords: ddc:000
    Language: English
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    A numerical reinvestigation of the Aoki phase with $N_f=2$ Wilson fermions at zero temperature (2003)
    Details
    Publication Date: 2014-02-26
    Description: We report on a numerical reinvestigation of the Aoki phase in lattice QCD with two flavors of Wilson fermions where the parity-flavor symmetry is spontaneously broken. For this purpose the Hybrid Monte Carlo algorithm was used and an explicit symmetry-breaking source term $h\bar{\psi} i \gamma_{5} \tau^{3}\psi$ was added to the Wilson fermion action. The order parameter $\langle\bar{\psi}i\gamma_{5}\tau^{3}\psi\rangle$ was studied at several values of $(\beta,\kappa,h)$ on lattices of sizes $4^4$ to $12^4$. Our largest lattices can be considered as infintely large allowing to extrapolate to $h=0$. The existence of a parity-flavor-breaking phase can be confirmed at $\beta=4.0$ and $\beta=4.3$ while we find no sign of parity-flavor-breaking at $\beta=4.6$ and $\beta=5.0$.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Clustering by using a simplex structure (2003)
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    Publication Date: 2014-02-26
    Description: In this paper we interpret clustering as a mapping of data into a simplex. If the data itself has simplicial struture this mapping becomes linear. Spectral analysis is an often used tool for clustering data. We will show that corresponding singular vectors or eigenvectors comprise simplicial structure. Therefore they lead to a cluster algorithm, which consists of a simple linear mapping. An example for this kind of algorithms is the Perron cluster analysis (PCCA). We have applied it in practice to identify metastable sets of molecular dynamical systems. In contrast to other algorithms, this kind of approach provides an a priori criterion to determine the number of clusters. In this paper we extend the ideas to more general problems like clustering of bipartite graphs.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Ein neues Verfahren zur Lösung des Streuproblems der Maxwell-Gleichungen (2003)
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    Publication Date: 2016-06-09
    Keywords: ddc:000
    Language: German
    Type: masterthesis , doc-type:masterThesis
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    Jahresbericht 2002 (2003)
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    Publication Date: 2019-10-24
    Keywords: ddc:000
    Language: German
    Type: annualzib , doc-type:report
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    Semantic Annotation in Mathematics and Math-Net (2003)
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    Publication Date: 2022-04-11
    Description: The Web of the future will provide a huge amount of information. We need better ways for dealing with and managing the information. A qualified semantic annotation of the information plays a key role for the Web of the future. This article gives an overview about the efforts of the mathematical community to build up a distributed and open information and communication system for mathematics: the Math-Net. The Math-Net Initiative has developed metadata schemas for some classes of Web resources which are relevant in mathematics. Math-Net Services process this information and enable the user to efficiently search and access the information.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    A new Finite Element realization of the Perfectly Matched Layer Method for Helmholtz scattering problems on polygonal domains in 2D (2003)
    Details
    Publication Date: 2022-07-07
    Description: In this paper we propose a new finite element realization of the Perfectly Matched Layer method (PML-method). Our approach allows to deal with arbitrary shaped polygonal domains and with certain types of inhomogeneous exterior domains. Among the covered inhomogeneities are open waveguide structures playing an essential role in integrated optics. We give a detailed insight to implementation aspects. Numerical examples show exponential convergence behavior to the exact solution with the thickness of the PML sponge layer.
    Keywords: ddc:000
    Language: English
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  • 58
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    O-versus S-protonation in diaryl sulfoxides: A semi-empirical mo investigation: Comparison with solution studies in superacids (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 244-252 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The protonation of diphenyl sulfoxide and several substituted diphenyl sulfoxides was probed by the MNDO-PM3 method to gain a theoretical insight into the experimentally observed preference for stable diphenyl sulfoxonium ion formation (O-protonation) in 1:1 FSO3H - SbF5 (Magic Acid) - SO2. In agreement with solution studies, O- protonation is uniformly favored (by ca 17 kcal mol -1) over S-protonation. The differences in the heats of formation of protonated and unprotonated diphenyl sulfoxides are increased by electron-withdrawing substituents (F, CF3) and decreased by electron-donating groups (Me, OMe). Variations in the SO bond length and bond order in the onium ions are compatible with simple resonance arguments and the oxonium/sulfonium character of both the O- and S-protonated onium ions. Surprisingly, the O- and S-protonated dibenzothiophene S-oxides are predicted to have identical energetics as compared with the corresponding protonated diphenyl sulfoxides. On structure optimization dibenzothiophene S-oxide itself, if the initial geometry is somewhat twisted, rearranges by ring expansion to give a new heterocycle with lower energy. A rotational barrier study on the parent O-protonated diphenyl sulfoxide showed two minima, separated by 1.3 kcal mol-1, at HOSC dihedral angles of 60° and 240°. The two conformations correspond to syn and anti orientations of the OH proton relative to the aromatic rings, and support the lowtemperature solution observations of the presence of two distinct sulfoxonium ions in solution. The rotational barriers for diphenyl sulfoxonium cation are compared with those of O-protonated dimethyl sulfoxide.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050505
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    Theoretical studies on nitrile-forming elimination reactionsDetermination of Reactivity by MO Theory, Part 73. Part 72, 1. Lee, C. K. Kim, B. H. Kong and B. C. Lee, J. Phys. Org. Chem. 4, 449 (1991). (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 259-268 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The base-promoted nitrile-forming elimination reactions of YCH=CHCβH=NOCH=CHZ (Y=OCH3, H or Cl and Z=H or NO2) were studied by the AM1 MO theoretical method with Cl- as a base. The reaction is found to proceed by an E1cB-like E2 mechanism in which Cβ - H bond cleavage is more advanced than N - O bond breaking. The syn-elimination has a more E1cB-like transition state (TS) than the anti elimination, which is attributed to the structurally favourable nN - ó * (Cβ - H) charge-transfer interaction. An electron-withdrawing Y substituent lowers the activation barrier by stabilizing negative charge developed on Cβ in the TS. An electron-withdrawing substituent in the leaving group (Z = NO2) tends to enhance the anti relative to the syn elimination process by depressing the δ*(N - O) level, which in turn makes the nć - δ*(N - O) interaction more effective. The YCH=CH -  and  - CβH=N fragments are perpendicular in the TS, which is stabilized by delocalization of negative charge developed on the Cβ atom.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050507
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    Stabilization of molecular association: An AM1/PM3 study of tetrahalomethane-arene molecular complexes (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 253-258 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An AM1/PM3 study of several tetrahalomethane-arene molecular complexes is presented. The results indicate the existence of weak attractive non-dispersion interactions in some of these complexes, which can be rationalized in terms of multipole - multipole and multipole - induced dipole interactions. No evidence was found for the occurrence of charge transfer in the ground states of these complexes.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050506
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    Masthead (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050601
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  • 62
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    Direct measurement of the energy barrier for 1,2-chlorine atom migration in α-methyl-α-chlorobenzyl(chloro)crbene (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 285-286 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The first direct determination of a 1,2-chlorine atom shift in a chlorobenzylcarbene was achieved by nanosecond laser flash photolysis. Arrhenius activation parameters of Eact = 3.39 ± 0.14 kcal mol-1 and log [A(s-1)] = 10.98 ± 0.14 were obtained for 1,2-chlorine migration in α-methyl-α-chlorobenzyl(ch1oro)carbene. The lifetime of this carbene is considerably longer than previously estimated and the measured Eact, is in excellent agreement with that determined by product analysis.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050510
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  • 63
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    Alkylation of pyridinium-N-phenoxide betaine dyes with iodomethane: Substituent, solvent and temperature dependence (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 275-284 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate constants of the pseudo-first-order methylation reaction of seven substituted pyridinium-N-phenoxide betaine dyes by iodomethane, were determined by UV-visible spectrophotometry in nine different solvents. The influence of substituents on the position of the long-wavelength, intramolecular charge-transfer absorption band of the unsubstituted betaine dye can be described by a modified Hammett equation. The solvent-dependent absorption constant ρA correlates satisfactorily with the acceptor properties of the nine solvents used. The substituent-dependent alkylation rate constants (In k) correlate linearly with the Hammett substituent constants, whereas the solventdependence of in k follows a more complicated pattern. Temperature-dependent measurements of the rate of alkylation exhibit an isoenthalpic behaviour for all the betaines in all the solvents investigated, i.e. the Arrhenius activation energy is almost constant for all differently substituted betaines in a given solvent. Temperature-dependent measurements of the alkylation rate of the unsubstituted betaine in different solvents led to an isosolvent relationship, i.e. the corresponding Arrhenius plots show a common point of intersection. According to the theory of isokinetic relationships, this isosolvent behaviour is interpreted in terms of a resonant energy exchange between the reacting species and the surrounding heat-bath system, which in this particular case seems to be the betaine molecule itself.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050509
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    Quantitative aspects of chirality. I. Method of dissymmetry function (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 295-298 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: To study molecular features connected with chirality, a procedure for the quantitative estimation of the chirality level of compounds of different classes is needed. A procedure for estimating the molecular asymmetry level relative to mirror-reflection axes of symmetry, S1, S2, S4 and S6, has been developed. The geometrical mean of these parameters is the disymmetry function (DF). To calculate the DF, the molecule must be fixed in the coordinate system, transferred to the main axes of inertia.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050603
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  • 65
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    Quantitative aspects of chirality. II. Analysis of dissymmetry function behaviour with different changes in the structure of the model systems (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 299-307 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The efficiency of the developed method of dissymmetry functions was studied using various model systems. The alteration of the dissymmetry function was analysed with systematic variations of the bond lengths, valence angles and masses of atoms in model tetrahedra. The behaviour of the dissymmetry function was studied for conformationally labile systems and chiral polyhedra. In general, it was found that in all cases the alteration of the dissymmetry function is in agreement with the speculative representations of the changes in degree of chirality.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050604
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  • 66
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    Concerning the development of scales of solvent ionizing power based on solvolyses of benzylic substrates (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 287-294 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Based on analysis of recently reported measurements, it is suggested that, provided a sufficiently large set of specific rate measurements in a wide variety of solvent types is available, the negligible to moderate improvements in the correlations of other types of benzylic chlorides, which are gained by use of a benzylic chloride (in place of 1-adamantyl chloride) as the standard substrate, do not justify the development of new specialized scales of solvent ionizing power. A similar conclusion is reached concerning solvent ionizing power scales developed for use with benzylic p-nitrobenzoates. However, such scales could be helpful when specific rates of solvolysis in only a limited variety of solvents are available, e.g. when a change in mechanism severely limits the range of operation of one of the pathways. Contrary to a previous claim, variations in ion-pair return could be the cause of deviations from Grunwald-Winstein plots for solvolyses of benzhydryl chloride in fluorinated alcohol solvents; such effects could be coupled, at least in part, with variations in aromatic ring solvation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050602
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  • 67
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    Charge-transfer transition energies and the prediction of reactivity in electrophile-nucleophile reactions (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 317-321 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The differences between charge-transfer transition energies calculated for donor-acceptor pairs at infinite separation and values determined experimentally for the charge-transfer complex geometry vary according to the charge type of the pairs and within a group of fixed charge type. It is argued that these differences provide a guide to the slope of the state-correlation curves for the product configuration in electrophile-nucleophile reactions of the corresponding charge type and that the observed variation invalidates the use of the simple expression ΔE=fΛ-β with constant f, derived from the curve-crossing model, to estimate energy barriers to reaction.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050606
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  • 68
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    Quantitative aspects of chirality. III. Description of the influence of the structure of chiral compounds on their twisting power in the nematic mesophase by means of the dissymmetry function (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 308-316 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: For a number of chiral α,β-unsaturated carbonyl compounds, cyclohexanone and cyclohexenone derivatives, existing essentially in the form of single molecular conformation, the correlation dependences were established between the values of the calculated dissymmetry functions (DF) with respect to atomic masses and atom refractions, and the induction effectiveness of helical ordering in the nematic mesophase (twisting power). Such correlative dependencies, as the examples show, allow one to predict safely enough the twisting power of new substances with the ‘fixed’ molecular conformation. Types of dissymmetry functions and kinds of correlative dependences, the most acceptable for these reasons, were revealed. Dissymmetry functions formed on the basis of atom refractions (polarizabilities) describe the influence of the molecular structures of chiral compounds on the twisting power with higher accuracy than those that characterize the dissymmetry of the atomic masses distribution, according to the important role of the dispersion forces in the formation of helical ordering in liquid crystalline systems. The components characterizing the distribution dissymmetry of atomic refractions and masses with respect to the long and two shorter axes as the peculiar characteristics of biaxiality of chiral molecules describe the influence of the molecular structure on the twisting power with the same accuracy as the general DF do. Thus influence of chiral dopant molecules on the interactions between molecules in the uniaxial mesophases is negligible within the limits of the DF method. Based on the calculations for model systems it is established that the presence of the non-linear cinnamoyl fragment has a decisive influence on the molecular dissymmetry of the chiral α,β-unsaturated ketones. The alkyl groups influence the molecular dissymmetry only slightly, but it is important that their presence ensures the stabilization of the chiral conformer with the defined helicity of the cinnamoyl fragment.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050605
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    Solvent and secondary substrate isotope effects on the acid-catalyzed ketonization of acetophenone enol in aqueous solution (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 322-326 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enol of acetophenone was generated flash photolytically in aqueous solution by photosolvolysis of PhCBr=CH2 and photohydration of PhC≡CH and PhC≡CD, and rates of its ketonization were measured in dilute perchloric acid solutions in H2O and D2O at 25°C. The rate constants so obtained provide the solvent isotope effects, kH+/kD+ = 5.02 ± 0.08, and the secondary isotope effect for deuterium substitution at the β-position of the enol double bond, (kH/kD)β = 0.999 ± 0.014. Arguments are presented which show that these isotope effects requre a stepwise rather than a concerted mechanism for the ketonization reaction.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610050607
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    New kinetic methods. 2.For Part 1 of this series, see Ref. 5. An indirect measurement of ester formation and hydrolysis rates (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 334-340 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The use of an assistant reagent to monitor spectroscopically the concentration of compounds that lack chromophores is described. It is demonstrated, for example, that the concentration of an aliphatic alcohol (present during acidcatalyzed hydrolysis or esterification reactions) can be monitored continuously by addition of a small amount of chromium trioxide. From a knowledge of the rate law and the rate constants for chromic acid oxidations, - d [CrO3]/dt = k [alcohol] [CrO3], the concentration of alcohol can be determined at any time by monitoring the absorbance of chromic acid at 363 nm. The rate at which the concentration of the alcohol is changing can then be used to calculate rate constants for the corresponding esterification or hydrolysis reactions. Rate constants obtained in this way are compared with those previously obtained by use of direct methods, and the application of this approach to the study of kinetics under conditions not accessible by other methods is illustrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050609
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    Ionization constants of 5-furylmethylenehydantoins and 5-thienylmethylenehydantoins in 80% (w/w) dimethyl sulphoxide-water at 25°C (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 349-354 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ionization constants of sixteen 5-furylmethylenehydantoins and 5-thienylmethylenehydantoins were measured in 80% (w/w) dimethyl sulphoxide-water solvent at 25°C. The effects of the 2-/3-furyl and 2-/-3-thienyl rings and the effects of configuration and conformation on acidity are discussed. The very low acidity of (Z)-5-(2-furyl)methylene-3-methylhydantoin suggests the possibility of some weak intramolecular interaction between the proton at N-1 and the 2-furyl oxygen in the s-cis conformation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050611
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    Reactions of molecules with two equivalent functional groups. 3. Nucleophilic substitution reactions of α, ω-dibromoalkanes [Br(CH2)nBr, n = 3,4,5] with potassium cyanide (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 327-333 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The substitution reactions of Br(CH2)nBr(1, n = 3-5) with KCN in methanol were studied in detail. Second-order rate constants k1 [formation of the mononitrile (2) from 1] and k2 (formation of the dinitrile (3) from 2) were determined, as were the rates for the reaction of H(CH2)nBr (4, n = 3-5) with KCN under the same conditions. The ratios k2/k1 ( = x) of the three homologs of 1 were found to be 1.15, 0.77 and 0.61 for n = 3, 4 and 5, respectively; a x value of 0.5 indicates that the functional groups behave independently. The second-order rate constants k1 (statistically corrected) and k2 exhibit modest enhancements compared with model compound 4 when any of the following substituents are present: δ or ∊-bromo, γ-, δ-, or ∊-cyano. By contrast, a γ-bromo substituent slightly retards the rate. These results indicate that the functional groups do influence each other to a modest degree by field effects which accelerate the reactions. Steric effects do not appear to play a significant role.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610050608
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    Catalysis in nucleophilic aromatic substitution reactions. A reinvestigation of the reaction between 1-fluoro-2,4-dinitrobenzene and n-butylamine (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 429-434 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction between 1-fluoro-2,4-dinitrobenzene and n-butylamine in toluene shows a two-step plot of kobs, values vs the initial values of the concentration of the amine. The usual base-catalysis mechanism for HF elimination from the zwitterionic intermediate hardly explains this kinetic behaviour and the kinetic effect of addition of salts (and of 2-hydroxypyridine) to the reaction mixtures at different initial values of the concentration of n-butylamine. In contrast, the kinetic behaviours are easily explained by the presence of substrate-amine (or catalyst) interactions on the pathway of the substitution reaction.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050707
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    Comparative study of aromaticity in five-membered rings containing S, SO and SO2 groups (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 74-82 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Owing to the importance of the concept of aromaticity, different indices have been developed to try to quantify this property. The possible π delocalization through an X—SOn—X group (X = C, N; n = 0, 1 or 2) could explain heteroaromaticity in rings containing the moiety. For that reason, the aromaticity of five-membered sulphurcontaining rings with different oxidation numbers (S, SO and SO2) and including no (thiophene), one (isothiazole) or two (1,2,5-thiadiazole) adjacent atoms was investigated. Ab initio calculations were carried out to determine geometrical parameters (planarity of the ring, bond length and bond order), electronic structure (charge distribution and dipolar moment) and the participation of d-orbitals of sulphur. According to these calculations, only compounds with S(II) can be considered to be aromatic, whereas compounds bearing S(IV) or S(VI) are better described as ylides.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050203
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    Hydrolyses of terpenoid diphosphates. Effects of azide ion on products of hydrolysis (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 83-92 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrolysis of geranyl diphosphate (GPP) at pH 7 in water gives largely linalool (LOH) + geraniol (GOH) in the ratio of 3:1. Added N-3 generates mixed acylic allylic azides and increases the LOH GOH ratio to 15:1 in 2 M NaN3, but does not speed up the overall reaction. Hydrolysis of neryl diphosphate (NPP) gives largely α-terpineol (TOH) +p LOH, but their ratio is not very sensitive to NaN3 concentration although acyclic azide and small amounts of α-terpinyl azide (TN3) are formed. Hydrolysis of α-terpinyl diphosphate (TPP) gives large amounts of the cyclic alkenes, limonene and terpinolene. Added N-3 does not change the amount of elimination, but increases the ratio of limonene to terpinolene, and diverts some substitution product to TN3. Trapping of carbocationic species from GPP by N-3 is sharply increased by addition of Mn2+, which also catalyzes the overall reaction. Products of reaction of GPP are derived from acyclic intermediates and of NPP from acyclic and cyclic intermediates, and ionizations of the three substrates do not generate common carbocationic species.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050204
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    Cyclopropylmethoxycarbene: A kinetic limit on the 1,2-carbon migration (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 104-107 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclopropylmethoxycarbene undergoes ambiphilic-nucleophilic intermolecular reaction with alkenes and methanol, but its intramolecular chemistry (1,2-carbon migration) is suppressed (k 〈 3 × 103 s-1) by the α-methoxy substituent.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050207
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    Masthead (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050301
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    Chemiexcitation of an anthraquinone derivative in the thermal cycloreversion of a dewar-anthraquinone derivative (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 101-103 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dewar-anthraquinone (1a) and 1,2,3-tri-tert-butyl-5,8-Dewar-anthraquinone (1b) were synthesized. Thermodynamic parameters for their cycloreversion to the corresponding anthraquinones indicate that thermal population of the excited states of the products via non-adiabatic valence isomerization is energetically feasible. On thermolysis of 1b, the formation of a detectable amount of 1,2,3-tri-tert-butyl-1,4-Dewar-anthraquinone (3) was observed. The excited singlet state of 1,2,3-tri-tert-butylanthraquinone (2b) produced via the non-adiabatic process is responsible for the formation of 3.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050206
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    Molecular modelling of organophosphorus podands and their complexes with alkali metal cations (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 109-118 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A molecular mechanics study on some organophosphorus podands, with both rigid and flexible terminal groups, and on their complexes with Li+ and Na+ was carried out. Na+ causes smaller deformations of the ligands than Li+, but its complexes are less stable, as the interaction energy with the podands is weaker. The ligands with rigid terminal groups are, in general, more pre-organized for complex formation. The cation-ligand interaction energies, including also the changes in steric energies, are always higher in complexes of flexible molecules than in those containing rigid ligands. The lower entropy losses which accompany the formation of complexes of rigid molecules with alkali metal cations probably account for the observed higher stabilities of the complexes.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050302
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  • 80
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    Hammett reaction constants for irreversible electroreduction of iodobenzenes in non-aqueous solvents (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 119-122 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polarographic half-wave potentials for the electrochemical reduction of a series of para-substituted iodobenzenes in acetonitrile, acetone, benzonitrile, dimethylformamide, dimethyl sulphoxide and methanol obey Hammett equations and the reaction constant found, ρ = 0·36 ± 0·02, is independent of the solvent used. The results obtained are discussed on the basis of a mechanism of the electrode process.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050303
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  • 81
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    Enthalpies of solution and intermolecular forces. tert-butyl halides in hydroxylic solvents (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 93-100 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The application of cavity theories of solution and linear solvation energy relationships to the interpretation of enthalpy of solution values of tert-butyl halides in hydroxylic media, measured at 25 °C and infinite dilution, is deserted, in order to define the intermolecular forces acting between solutes and solvents. It is concluded that solvent dipolarity and solvent HBD acidity effects dominate the solution process. An empirical equation relating the enthalpies of solution with selected properties of both solvents and solutes is proposed. New experimental Δ Hs∞ values for tert-butyl iodide in 13 alcohols are reported.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050205
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  • 82
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    Laser flash photolysis study of 10, 10-dimethyl-9-anthrylidene, a carbene with nearly degenerate singlet and triplet states (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 123-128 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 10, 10-Dimethyl-9-anthrylidene (DMA) was studied by laser flash photolysis (LFP) techniques. LFP of the requisite diazo precursor in pentane or carbon tetrachioride produced transient spectra attributed to the hydrocarbon and monochlorinated diarylmethyl radicals, respectively. In the presence of pyridine and oxygen, ylides were formed upon LFP of 10, 10-dimethyl-9-diazoanthrone. However, ylides are not formed in acetonifrile or acetone. The carbene itself was not detected by transient absorption spectroscopy. The absolute rate constants for reaction of DMA with pyridine, methanol and triethylsilane are 1·96 × 109, 1·8 × 1010, and 1·0 × 108 I mol-1 s-1, respectively. It is concluded that the singlet and triplet states of DMA are essentially degenerate.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050304
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    Transimination reaction between pyridoxal-5′-phosphate schiff bases with dodecylamine and amino acids (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 142-154 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Some transimination processes were studied using an intermolecular model formed by pyridoxal-5′ -phosphate (PLP) an amino acid and dodecylamine (DOD) in an aqueous medium. All the kinetic constants for the reversible reaction were determined. The results show that in these cases transimination proceeds through an addition-elimination by forming a diamine geminal intermediate. Equilibria are always shifted to dodecylamine-PLP Schiff base formation. Differences between the stability of this Schiff base and the ∊-aminocaproic Schiff base cannot be explained only on the basis of the different nucleophicities of amine groups and therefore differences in the imine double bond environment must be taken into account to explain this behaviour.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050306
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  • 84
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    Cycloaddition of heterofunctionalized allenes with tert-butylthioacrylonitrile. Determination of activation parameters for diradical intermediate formation and the detection of reversible ring closure (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 160-170 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The cycloaddition reactions of 4-methylphenylthio-, methoxy-, 4-methoxyphenyl-, phenyl-, chloro- and cyanoallene with tert-butylthioacrylonitrile (BTA) in toluene-d8 solution were investigated. The relative reactivity sequence of these substituted allenes is 4-methylphenylthio ∼ methoxy- 〉 4-methoxyphenyl- 〉 phenyl- 〉 chloro- 〉 cyanoallene. Activation parameters were measured for diradical intermediate formation of BTA with 4-methylphenylthio-, methoxy- and 4-methoxyphenylallene, giving average values of Ea and ΔS± of 14.2-16.8 kcal mol-1 and ca. -33 eu, respectively. The relative reactivity sequence is consistent with a FMO allene-HOMO, BTA-LUMO dominant interaction for diradical intermediate formation. However, the regioselectivity of attack on the substituted allene appears to be thermodynamically controlled. The formation of the diradical intermediates in these cycloaddition processes appears to be irreversible. However, the ring closure of the diradical intermediates formed from 4-methylphenylthio-, methoxy- and 4-methoxyphenylallene is reversible under the conditions of the kinetic experiments. The kinetically controlled ring closure of the diradical intermediates is allyl radical SOMO controlled, while the final cycloadduct distribution is thermodynamically controlled.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050308
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    Masthead (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050401
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    Protonated propylene oxide is stable towards isomerization in the gas phase (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 201-208 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative stabilities of gaseous protonated propylene oxide and its isomers, protonated propanal, oxetane and acetone, were reinvestigated in a Fourier transform ion cyclotron resonance mass spectrometer by using multiple-stage tandem mass spectrometri experiments. The dependence of ion structure on internal energy was examined by generating the ions in proton transfer reactions with different exothermicities and then probing their structures by using energy-resolved mass spectrometry (collision-activated dissociation as a function of collision energy). In contrast to results obtained in several recent investigations, protonated propylene oxide was found to be distinct from its more stable isomers when generated with only a small amount of internal energy. When the exothermicity of the proton transfer reaction was higher than 6 kcal mol-1 (1 kcal = 4·184 kJ) or when the epoxide ion was subjected to multiple activating collisions, rapid isomerization to protonated propanal occurred. The energy required for opening of the epoxide ring estimated to be similar to that measured earlier for protonated cyclohexene oxide (5-10 kcal mol-1).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050405
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  • 87
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    ESR study of solvent effects on the electronic structure of 2-(4′ -dialkylaminophenyl)indan-1,3-dionyl radicals (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 218-224 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ESR spectra of 2-arylindan-1,3-dionyl radicals in various solvents at 343 K were obtained and assignments of the hyperfine structures were made. The hyperfine coupling constant (hfcc) of the dimethylamino nitrogen increases whereas the 2',6'-hydrogen hfcc decreases as the ET value, a solvent polarity parameter, increases. MO calculations were made according to the semi-empirical procedure of Rieger and Fraenkel; the nitrogen and oxygen Coulomb integrals were adjusted so that the calculated spin density on the nitrogen atom agrees with that estimated from its hfcc. It is found that the π-moment of the radicals increases from 9·13 D in toluene to 9·85 D in acetic acid. The solvent dependence of the equilibrium between the radicals and its dimer has been explained in terms of the solventinduced π-moment in polar solvents.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050407
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  • 88
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    Heats of formation of organic molecules by ab initio calculations. Aldehydes and ketones (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 225-229 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A bond and group equivalent scheme that allows the calculation of heats of formation for aldehydes and ketones from ab initio 6-31G* energies has been developed. For a group of 24 aldehydes and ketones, the RMS error for the calculated heat of formation was 0 · 46 kcal mol-1. Heats of formation have been predicted for an additional seven compounds for which the experimental values are believed to be either in error or unknown. There are some problems with the norbornanones.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610050502
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    Substituent effect on the relative strength of some arylthiomethyl- and arylsulphonylmethylbenzoic acids (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 239-243 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The pK values of some arylthiomethylbenzoic acids and the corresponding sulphones were determined spectrophotometerically. The role of substituent and the position of the carboxylic group are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050504
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    Experimental and theoretical study of the influence of the solvent on asymmetric diels - alder reactions (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 230-238 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate, endo/exo and diastereofacial selectivities of the Diels-Alder reaction between cyclopentadiene and ( - )-menthyl acrylate were measured in a series of organic solvents and organic-aqueous mixtures. Regression analyses show that a model with the α empirical solvent parameter accounts for most of the changes in rates and diastereofacial selectivities, whereas in the case of the endo/exo selectivity, inclusion of the π* and δ parameters is needed. Theoretical calculations carried out on the model reaction between methyl acrylate and cyclopentadiene using dielectric continuum and supermolecule models do not clearly show the effect of the different solvation mechanisms on rate. However, they agree with the above-mentioned influence of α and π* on the endo/exo and diastereofacial selectivities.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050503
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  • 91
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    Enhancement or suppression of CIDNP intensities by a second magnetic nucleus: Interplay between g factor difference, external magnetic field, and hyperfine coupling constants (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 209-217 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enhancement factors of the 1H polarization induced in radical pairs generated by α-cleavage of 12C=O- and C=O-labelled ketones deviate from the ratios expected on the basis of the relative abundances of the respective carbon isotopomers. For dibenzyl ketone, the ratio of absolute CIDNP intensities of the 1H(13C) doublet (90% 13C=O) to the 1H(12C) singlet (10% 12C=O) was found to be 〉9:1 at 58·3 kG and 〈9:1 at 21 kG. Similar deviations were observed for other 13C labelled ketones, viz. deoxybenzoin (13C=O) and acetophenone (13C=O or 13CH3). This novel enhancement or suppression effect on the CIDNP enhancement can be ascribed to the presence of a second hyperfine coupled nucleus in the intermediate radical pair. The individual contributions of the g factor difference (Δg), the external magnetic field strength (Ho), and the hfc constants of the observed (aA) and the interacting nucleus (ax) in the enhancement-suppression are exemplified. The experimental results are consistent with theoretical calculations of the mutual effect of Δg, H0, aA and ax on the CIDNP enhancement factor of the observed nucleus.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050406
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    Reduction of 1-benzyl-3-cyanoquinolinium ion by phosphonate: Solvent effects in propan-2-ol-water mixed solvents (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 269-274 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants (k2) were determined for the reduction of 1-benzyl-3-cyanoquinolinium ion by phosphonate dianion in mixed solvents consisting of propan-2-ol and water. The reduction product was mostly 1-benzyl-3-cyano-1,4-dihydroquinoline with a trace of the 1,2-isomer. The solvent properties were varied by increasing the fraction of water in the mixed solvent, which increases the polarity of the solvent. Increasing the proportion of alcohol makes the solvent a better electron pair donor. The higher fraction of propan-2-ol in the mixed solvent gives rise to a substantial increase in k2. A quantitative comparison of the solvent effect on this reaction with the solvent effects on related reactions suggests a solvent Brønsted α value of 0·45. This suggests that the PO3- unit of the transition state interacts only weakly with the solvent although the final oxidized product is phosphate.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050508
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    Interaction of formamide with stilbazolium betaines: Steric effects in amides (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 609-613 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The visible spectrum of di-tert-butylstilbazolium betaine (DTBSB) was recorded in eight simple amides. The appearance of a ‘coarse’ structure in the main absorption band is due to the shielding effect of the tert-butyl groups, which hinder the approach of the solvent. Since this structure disappears in formamide, it is concluded that this solvent associates through its NH to the carbonyl group of DTBSB. For the other amides, there is a clear relationship between the steric effect, for both the N- and C-substituents, of the solvent-solute hydrogen bond association and the structure of the visible band.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610050909
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    Structure of, and internal rotation in, hexakis [4-(2-phenylpropan-2-yl) phenoxy] benzene, and structural comparison with its precursor phenol 4-(2-phenylpropan-2-yl)Phenol (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 628-632 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The title compounds (1 and 3, respectively) were studied by X-ray crystal structure analysis. Both are trigonal, space group R3, with lattice parameters a = 27.718(6), c = 8.161(2) Å, Z = 3 and a = 31.267(7), c = 6.560(2), Z = 18, respectively. The dodecamethyl compound 1 is isomorphous with its parent hexakis(4-benzylphenoxy)benzene (2), a known host. However, ‘collapse’ along the c-axial direction has occurred such that the appreciable clathrate cavity of 2 has been replaced by only a very small residual void for 1. Phenol 3 does not pack in discrete [OH]6 hydrogenbonded hexamers; instead, molecules are assembled in infinite chains, linked by OH…O hydrogen bonds of length 2.735(3) Å, which are propagated along threefold screw axes. A variable-temperature CPMAS NMR study of sidechain aryl group rotation in 1 gives a value ΔG≠ of 14.0 ± 0.7 kcal mol-1 (at 42 °C) for the (crystallographically unique) para -disubstituted ring, a similar 14 kcal mol-1 free energy barrier being found hindering rotation of this ring, and of the outer phenyl ring of 1, at 9°C.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051003
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    Diastereofacial selectivity in 1,3-dipolar cycloadditions to cyclobutens. 8. HF/3-21G transition structures of the reactions of formonitrile oxide with CIS-3,4-dichlorocyclobutene and norbornene (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 819-823 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A transition structure for the syn and anti attack of formonitrile oxide on both cis-3,4-dichlorocyclobutene and norbornene was obtained using HF/3-21G method. These calculations correctly predict dominance of the syn attack in the reaction of dichlorocyclobutene and 100% syn selectivity, with respect to the methano bridge, in the reaction of norbornene. Analysis of the activation energy shows that the inherent facial bias of dichlorocyclobutene is reflected, at the transition state, in a complex way in the deformation energy of both dichlorocyclobutene and formonitrile oxide and in the interaction energy between them. With norbornene the out-of-plane deformation energy of the olefinic hydrogens clearly emerges as the major factor in controlling facial selectivity.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051207
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    Electronic Resource
    Masthead (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051001
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  • 97
    Electronic Resource
    Electronic Resource
    Effect of hexadecyltrimethylammonium bromide micelles on the rate of oximolysis of esters (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 341-348 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two amphiphilic oximes, 10-phenyl-10-hydroxyiminodecanoic acid (oxime II) and 4-(9-carboxynonanyl)-1-(9-carboxy-1-hydroxyimino nonanyl)benzene (oxime III) were synthesized. The pKa values of oximes II and III and acetophenoxime (oxime I) and the rates of oximolysis of p-nitrophenyl acetate (NPA) and p-nitrophenyl octanoate (NPO) were determined in the presence and absence of micellar hexadecyltrimethylammonium bromide (CTAB). The rates of oximolysis increased by up to 3 × 104-fold in the presence of CTAB. Quantitative analysis of micellar effects, using an ion-exchange pseudo-phase model, allowed the determination of the second-order rate constants for the reactions of oximes I-III with NPA and NPO in the micellar pseudo-phase. The calculated rate constants in the micellar pseudo-phase were lower than those in water, demonstrating that the rate enhancements were due to substrate concentration in the micelles. Comparison of the rate constants in micelles and water suggests that the sites of reaction of oximes I-III with NPO and NPA are similar to those in bulk aqueous solution. Micellar incorporation of the hydrophobic oximes II and III does not lead to a major change in the nucleophilicity of the oximate anion.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050610
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  • 98
    Electronic Resource
    Electronic Resource
    Photochemical reactions of 2,2′-furil. Solvent dependent photoreduction via the lowest excited singlet and triplet states (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 355-360 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2,2′-Furil (di-2-furyl diketone) undergoes photoreduction to give furoin on irradiation at 366 nm in triethylamine-containing benzene and ethers. On the other hand, in ethanol the photoirradiation leads to the formation of an enediol type of compound, 1,2-di(2-furan)ethene-1,2-diol. The results of quenching and sensitization both for the photoreactions and the phosphorescence demonstrate that furoin and the enediol are formed via the lowest excited singlet and the triplet states of 2,2′-furil, respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050612
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  • 99
    Electronic Resource
    Electronic Resource
    Masthead (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050701
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    Paper (German National Licenses)
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  • 100
    Electronic Resource
    Electronic Resource
    Quantum mechanical and molecular mechanical studies of the hydrolysis of methyl nitrate and the solvent effect (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 361-366 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alkaline hydrolysis reaction of methyl nitrate was simulated by quantum mechanical and molecular mechanical methods. The gas-phase reaction was calculated to proceed with no barrier when ab initio calculations at the STO-3G level were utilized, and with a very small barrier (5.70 kJ mol-1) when the MINDO/3 method was applied. In solution, the solvation energy was estimated to be 70.33 kJ mol-1 by molecular mechanical calculations. Thus the activation energy (76.03 kJ mol-1) of alkaline hydrolysis of methyl nitrate was found to be in good agreement with the available experimental value (82.42 kJ mol-1). The results indicated that the substantial activation barrier in alkaline hydrolysis was essentially solvent-induced.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050613
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