Chemistry

Cycloalkane structures


Cycloalkanes: cyclobutane

The cyclobutane molecule is not flat, but folded. The molecule folds out of the plane so that the tension generated by the eight eclipsed hydrogen atoms is reduced. Part of the molecule is rotated 26 ° out of plane. However, this does not mean that the structure is rigid; it flips from one folded conformation to the other very quickly. The C-C-C angle of 88.5 ° is also significantly removed from the tetrahedral angle (109.5 °) and indicates a high ring tension.

The dissociation energy of the C-C bond in cyclobutane is 264 kJmol-1 very low. With ring opening, as with cyclopropane, tension is released and new bonds are formed with greater overlap. Cyclobutane, although less reactive than cyclopropane, undergoes similar reactions.


Cycloalkanes

the Cycloalkanes (Cyclanes, older name: Naphthenes, cycloparaffins) are a group of substances made up of ring-shaped, saturated hydrocarbons. The rings can have side chains. In the systematics of organic chemistry they are one of the alicyclic compounds. The cycloalkanes without side chains form a homologous series with the general empirical formula C.nH2n, where n ≥ 3. Thus, the smallest occurring cycloalkane is cyclopropane.


Table of contents

Naturally occurring cycloalkanes (cyclopentane, cyclohexane, cycloheptane) were first found by the chemist Vladimir Wassiljewitsch Markovnikov in the petroleum fraction, also called naphtha, of the Caucasian petroleum. Hence the name Naphthawhich is occasionally used for all cycloalkanes. Usually this imprecise name is only used for the derivatives of cyclopentane and cyclopentane. In the language of the petroleum industry, naphthene is still a common name for these cycloalkanes.


Cycloalkenes

- have at least one double bond

- are alkenes, the molecules of which are ring-shaped

- They hardly differ from the alkenes in terms of properties and reaction behavior

- The position of the double bond does not have to be specified because it is a closed chain (only applies to a double bond)!

Cycloalkanes also have isomers, namely cis-trans isomers. If the substituents are on the same side, one speaks of cis isomers, but when the substituents are on different sides, one speaks of trans isomers.


Historical

Karl Weltzien, the first full professor of organic chemistry (1848-1869) is best known as the organizer of the first international conference for chemists in Karlsruhe in 1860. Hermann Staudinger began his academic career here as an assistant and C-3 professor (1907-1912 ) with work on ketenes, ozonolysis, autoxidation, diazo compounds and macromolecules. Karl Freudenberg dealt with lignins, polysaccharides and stereochemical topics during his time in Karlsruhe (1922-1926). His successor, Stefan Goldschmidt (1927-1935) concentrated his work on free organic radicals from carbon, nitrogen and oxygen. Rudolf Criegee (1937-1969) made a considerable contribution to the development of organic chemistry. His work on the mechanism of ozonolysis, autoxidation processes, dihydroxylation with osmium tetroxide and high-tension hydrocarbons are internationally known. In 1966 the institute was relocated to a new building. Around this time the number of chairs was increased to three. Kurt Hasse (1966-1971) was a bio-organic chemist, Hans Musso (1968-1988) clarified the structures of various natural dyes, and Gerhard Schröder (1970-1997) worked on bull valenes, annulenes, crown ethers and carbon oxides.


Discrete and Algebraic Structures - In Brief

This text and study book presents the topics that are usually dealt with in the standard lecture on discrete structures. The presentation is aimed at students of computer science and mathematics (teaching post and Bachelor / Master) and is designed to accompany lectures, for self-study and for exam preparation.

Numerous tasks make it easier to deepen the subject matter. Thanks to the compact presentation of all important discrete and algebraic structures and the extensive index, the book is also suitable as a reference work for mathematicians, computer scientists and natural scientists.

Contents: From propositional and predicate logic to sets and combinatorics, numbers, relations and figures, graphs to the rich spectrum of algebraic structures and a brief insight into category theory.

The 2nd edition has been completely reviewed and, in addition to additional chapters on rings and modules as well as matroids, now also includes typical exam tasks for the first time.

Prof. Dr. Dr. h.c. Ulrich Knauer is Professor of Mathematics at the Carl von Ossietzky University of Oldenburg.

Dr. Kolja Knauer is Maître de Conference for discrete mathematics and computer science at the University of Aix-Marseille.


Basics of logistics

Authors: Muchna, C., Brandenburg, H., Fottner, J., Gutermuth, J.

  • Didactically prepared learning content for self (distance) study
  • Very clear presentation
  • With numerous exercises and detailed solutions

Buy this book

  • ISBN 978-3-658-18593-0
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This book provides a basic introduction to logistics and a classification of logistics in the value creation process. The question of the relationship between logistics (management) and supply chain management is also examined. In addition to terms and structures in logistics, process aspects are also dealt with. The aim is to show in a compact form the modern understanding of logistics that goes beyond the pure physical handling of goods transports, transshipment and storage. Logistics is treated both from the perspective of a management concept and from the perspective of technical dimensions. Each chapter contains learning objectives as well as numerous exercises with detailed solutions for self-study and for optimal exam preparation.

Prof. Dr. Claus Muchna teaches general business administration at the Hamburger Fern-Hochschule. Before that, he held various management positions in national and international logistics companies.

Hans Brandenburg, a qualified commercial teacher, was a department head at the vocational school for forwarding, logistics and transport in Hamburg.

Prof. Dr.-Ing. Johannes Fottner holds the chair for materials handling, material flow, logistics at the Technical University of Munich. He was managing director of the MIAS Group and held various management functions at Swisslog AG.

Jens Gutermuth, graduate commercial teacher, is department head at the vocational school for forwarding, logistics & traffic in Hamburg and head of the HFH study center for the Hamburg bachelor's degree in logistics.


Who we are - what we do

The GDCh Macromolecular Chemistry specialist group brings together scientists from universities, research institutes and industry and bundles expertise from the areas of polymer chemistry, physics and applications:

  • Polymer synthesis and modification (synthetic polymers & biopolymers, hybrid materials & composites, nanocomposites etc.)
  • Polymer physics and characterization (structure elucidation & representation of structure-property relationships)
  • Industrial polymers / polymer materials and their applications
  • Functional polymers with tailor-made properties and polymer-based systems (devices)
  • New developments in the polymer sector (e.g. polymers based on renewable raw materials, polymers and systems with (switchable) functions for electronics, optics and medical technology, biomaterials)


Through intensive internal and external exchange, the specialist group faces the current challenges in research, application and training in the field of macromolecular sciences and makes an effective contribution to maintaining and promoting the competitiveness of Germany as a science and business location.


Welcome to the working group of Prof. Herbert Pfnür

The physical and chemical properties of ultra-small structures are mainly determined by their borders and edges. Hence, they can be manipulated and controlled through their interfaces. This is possible for all nano-objects and this possibility is becoming more and more important with advancing miniaturization, e.g. in microelectronic circuits through the use of ultra-small and ultra-fast chip architectures or in the design of new catalysts. The scientific scope of interfaces and their relevance for application was once again underlined in 2007 by the Nobel Prize in Physics and Chemistry (Grünberg, Fert and Ertl).

In this context, our working group is mainly interested in the formation, characterization and manipulation of ultra-small structures on surfaces ranging in size from a few nanometers to individual atoms and their fundamental physical properties. Structures such as ordered arrays of atomic wires or non-contacts are created through a combination of established concepts of surface physics, in particular self-organization (bottom-up principle) and mesoscopic and macroscopic structuring (top-down principle). In this way, we are able, for example, to investigate the electronic properties and electrical transport of objects in zero, one or two dimensions. Questions about the relationship between these properties, the dependency of the material combination and their morphology are of great interest.

To answer these questions, a wealth of tools are required that should be both surface-sensitive and at the same time provide high-yield information on the atomic scale. These include tunnel microscopy (STM) and electron diffraction (LEED) as well as various types of electron spectroscopy (UPS, XPS and EELS).


Since February 2006, the departments of physics and chemistry have jointly operated the nanostructure laboratory at the University of Konstanz. On 160 m 2 there are devices available in the clean room to produce and examine structures on the nanometer scale. The equipment includes electron microscopes, lithography systems, coating and dry etching systems. The laboratory is open to all scientists at the University of Konstanz and is currently used by around 140 scientists from 14 working groups for their research.

The nanostructure laboratory has played a central role in the Collaborative Research Center SFB 767 & quotControlled Nanosystems & quot and is also an important part of the SFB 1214 & quotAnisotropic Particles as Building Blocks & quot. In addition to providing a wide variety of systems for nanostructuring and nanoanalysis, the nano laboratory also serves for scientific exchange and better networking between the groups.

First impressions

Thanks! This video was created by & quotMedienlabor AG Medienwissenschaft / Camera and Editing: Lukas Burg & quot as part of a web documentation for the 50th anniversary of the University of Konstanz.


Fire hazard and fire reduction

Hydrocarbons, whether liquid or gaseous, burn very quickly and with a hot flame the energy released is great. Liquid hydrocarbons with a low boiling point (gasoline) also evaporate easily and quickly, because of their low flash point, fires are easy to start. For these reasons, hydrocarbons serve as motor fuels and are therefore extracted, manufactured, transported and stored in large quantities.

In accidents with a fire break out e.g. B. in a refinery, the amount of energy released can lead to disasters, which make special precautions necessary to reduce possible damage. Materials with higher fire rate requirements are used here than are customary in normal structural fire protection. This also applies to tunnel construction in most industrialized countries, because in accidents with fuel transporters in tunnels, leaking fuel can catch fire, causing even the hardest concrete to flake off. For example, a fire in the Eurotunnel reduced the concrete ceiling in the submarine tunnel to a thickness of approx. 50 mm.

Wherever hydrocarbons are used, stored or transported, corresponding laws and regulations apply in order to largely reduce the risk of accidents. There are special containers that are only approved for the transport of hydrocarbons. Special international regulations also apply to petrol stations, such as a smoking ban in the entire petrol station area.

Usually, such regulations followed spectacular accidents that historically have caused a great deal of damage. There have also been some tunnel fires that first led to regulations for materials with increased fire rates in this area.


Video: K08 Δομές Δεδομένων - Γράφοι (January 2022).