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CAS, Chemical Abstracts Service Home Page
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Periodic Table of the Elements by WebElements [IUPAC]IUPAC.org Where to find MSDS and SDS on the Internet General Sites These sites have large collections of MSDS and are a good place to start your search. [Top] [General Sites] [Governmental] [Chemical Companies] [Pesticides] [Misc] Government and Non-Profit Sites The first two sites return all sorts of chemical information; the remainder are written more for humans rather than corporate lawyers and are good sites for non-chemists to find information. Chemical Manufacturers and Suppliers The best place to start if you have a bottle from that particular manufacturer! Pesticides (herbicides, insecticides, fungicides, nematicides, rodenticides etc.) A great place to start for farmers, home gardeners or someone who got too close to a crop dusting plane. Miscellaneous Look here for manufacturers whose primary business is not chemicals.

Mineralogy Database - Mineral Collecting, Localities, Mineral Photos and Data Stereoisomers Stereoisomers As defined in an earlier introductory section, isomers are different compounds that have the same molecular formula. When the group of atoms that make up the molecules of different isomers are bonded together in fundamentally different ways, we refer to such compounds as constitutional isomers. For example, in the case of the C4H8 hydrocarbons, most of the isomers are constitutional. Shorthand structures for four of these isomers are shown below with their IUPAC names. Note that the twelve atoms that make up these isomers are connected or bonded in very different ways. The bonding patterns of the atoms in these two isomers are essentially equivalent, the only difference being the relative orientation or configuration of the two methyl groups (and the two associated hydrogen atoms) about the double bond. Configurational Stereoisomers of Alkenes Some examples of this configurational stereoisomerism (sometimes called geometric isomerism) are shown below. Ethane Conformations

Category:Chemistry The main article for this category is Chemistry. Subcategories This category has the following 70 subcategories, out of 70 total. Pages in category "Chemistry" The following 98 pages are in this category, out of 98 total. Covalent radius The covalent radius, rcov, is a measure of the size of an atom that forms part of one covalent bond. It is measured either in picometres (pm) or ångströms (Å), with 1 Å = 100 pm. In principle, the sum of the two covalent radii should equal the covalent bond length between two atoms, R(AB) = r(A) + r(B). Moreover, different radii can be introduced for single, double and triple bonds (r1, r2 and r3 below), in a purely operational sense. These relationships are certainly not exact because the size of an atom is not constant but depends on its chemical environment. The bond lengths R(AB) are measured by X-ray diffraction (more rarely, neutron diffraction on molecular crystals). Table of covalent radii the covalent radius is measured approximately as the radius of an atom's core which is in contact with the core of an adjacent atom in a bonded situation A different approach is to make a self-consistent fit for all elements in a smaller set of molecules. References Log in / create account

2.8 Hindered Rotating Chain

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