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Van Der Waals Strain
In chemistry, van der Waals strain is strain resulting from van der Waals repulsion when two substituents in a molecule approach each other with a distance less than the sum of their van der Waals radii. Van der Waals strain is also called van der Waals repulsion and is related to steric hindrance.[1] One of the most common forms of this strain is eclipsing hydrogen, in Alkanes. In rotational and pseudorotational mechanisms[edit] In molecules whose vibrational mode involves a rotational or pseudorotational mechanism (such as the Berry mechanism
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Chemistry
Chemistry
Chemistry
is the scientific discipline involved with compounds composed of atoms, i.e. elements, and molecules, i.e. combinations of atoms: their composition, structure, properties, behavior and the changes they undergo during a reaction with other compounds.[1][2] Chemistry
Chemistry
addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron(s); ionic bonds, in which a compound donates one or more electrons to another compound to produce ions: cations and anions; hydrogen bonds; and Van der Waals force
Van der Waals force
bonds
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Potential Energy
U = m · g · h (gravitational) U = ½ · k · x2 U = ½ · C · V2 (electric) U = -m · B (magnetic)Part of a series of articles aboutClassical mechanics F → = m a → displaystyle vec F =m vec a Second law of motionHistory TimelineBranchesApplied Celestial Continuum Dynamics Kinematics Kinetics Statics StatisticalFundamentalsAcceleration Angular momentum Couple D'Alembert's principle Energykinetic potentialForce Frame of reference Inertial frame of reference Impulse Inertia / Moment of inertia MassMechanical power Mechanical workMoment Momentum Space Speed Time Torque Velocity Virtual workFormulationsNewton's laws of motionAnalytical mechanicsLagrangian mechanics Hamiltonian mechanics Routhian mechanics Hamilton–Jacobi equation Appell's equation of m
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Henry Rzepa
Henry Stephen Rzepa (born 1950)[1] is a chemist and Emeritus Professor of Computational chemistry
Computational chemistry
at Imperial College London.[8][5][9]Contents1 Education 2 Career and research2.1 Awards and honours3 ReferencesEducation[edit] Rzepa was born in London in 1950,[citation needed] was educated at Wandsworth
Wandsworth
Comprehensive School, and then entered the chemistry department at Imperial College London
Imperial College London
where he graduated in 1971
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Special
Special
Special
or specials may refer to:Contents1 Music 2 Film and television 3 Other uses 4 See alsoMusic[edit] Special
Special
(album), a 1992
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International Standard Book Number
"ISBN" redirects here. For other uses, see ISBN (other).International Standard Book
Book
NumberA 13-digit ISBN, 978-3-16-148410-0, as represented by an EAN-13 bar codeAcronym ISBNIntroduced 1970; 48 years ago (1970)Managing organisation International ISBN AgencyNo. of digits 13 (formerly 10)Check digit Weighted sumExample 978-3-16-148410-0Website www.isbn-international.orgThe International Standard Book
Book
Number (ISBN) is a unique[a][b] numeric commercial book identifier. Publishers purchase ISBNs from an affiliate of the International ISBN Agency.[1] An ISBN is assigned to each edition and variation (except reprintings) of a book. For example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, and 10 digits long if assigned before 2007
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Fluorine
Fluorine
Fluorine
is a chemical element with symbol F and atomic number 9. It is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. As the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine. Among the elements, fluorine ranks 24th in universal abundance and 13th in terrestrial abundance. Fluorite, the primary mineral source of fluorine which gave the element its name, was first described in 1529; as it was added to metal ores to lower their melting points for smelting, the Latin verb fluo meaning "flow" gave the mineral its name. Proposed as an element in 1810, fluorine proved difficult and dangerous to separate from its compounds, and several early experimenters died or sustained injuries from their attempts
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Chlorine
Chlorine
Chlorine
is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine
Chlorine
is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity, behind only oxygen and fluorine. The most common compound of chlorine, sodium chloride (common salt), has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, but not recognised as a fundamentally important substance. Carl Wilhelm Scheele
Carl Wilhelm Scheele
wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element
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Trigonal Bipyramidal Molecular Geometry
In chemistry a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular dipyramid. This is one geometry for which the bond angles surrounding the central atom are not identical (see also pentagonal dipyramid), because there is no geometrical arrangement with five terminal atoms in equivalent positions. Examples of this molecular geometry are phosphorus pentafluoride (PF5), and phosphorus pentachloride (PCl5) in the gas phase.[1]Contents1 Axial (or apical) and equatorial positions 2 Related geometries with lone pairs 3 Berry pseudorotation 4 See also 5 References 6 External linksAxial (or apical) and equatorial positions[edit]Trigonal bipyramidal molecular shape ax = axial ligand (on unique axis) eq = equatorial ligand (in plane perpendicular to unique axis)The five atoms bonded to the central atom are not all equivalent, and two different types of position are defined
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PCl5
Phosphorus
Phosphorus
pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moisture-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.Contents1 Structure1.1 Related pentachlorides2 Preparation 3 Reactions3.1 Hydrolysis 3.2 Chlorination of organic compounds 3.3 Comparison with related reagents 3.4 Chlorination of inorganic compounds4 Safety 5 History 6 See also 7 References 8 External linksStructure[edit] The structures for the phosphorus chlorides are invariably consistent with VSEPR theory. The structure of PCl5 depends on its environment. Gaseous and molten PCl5 is a neutral molecule with trigonal bipyramidal (D3h) symmetry
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PF5
Phosphorus
Phosphorus
pentafluoride, PF5, is a phosphorus halide. It is a colourless, toxic gas that fumes in air.[1][2] Preparation[edit] Phosphorus
Phosphorus
pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride, which remains a favored method:[1]3 PCl5 + 5 AsF3 → 3 PF5 + 5 AsCl3Structure[edit] Single-crystal X-ray studies indicate that the PF5 has trigonal bipyramidal geometry. Thus it has two distinct types of P−F bonds (axial and equatorial): the length of an axial P−F bond is distinct from the equatorial P-F bond in the solid phase, but not the liquid or gas phases due to Pseudo Berry Rotation. Fluorine-19 NMR
Fluorine-19 NMR
spectroscopy, even at temperatures as low as −100 °C, fails to distinguish the axial from the equatorial fluorine environments
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Bartell Mechanism
The Bartell mechanism is a pseudorotational mechanism similar to the Berry mechanism. It occurs only in molecules with a pentagonal bipyramidal molecular geometry, such as IF7. This mechanism was first predicted by H. B. Bartell. The mechanism exchanges the axial atoms with one pair of the equatorial atoms with an energy requirement of about 2.7 kcal/mol. Similarly to the Berry mechanism
Berry mechanism
in square planar molecules, the symmetry of the intermediary phase of the vibrational mode is "chimeric"[1][2][3] of other mechanisms; it displays characteristics of the Berry mechanism, a "lever" mechanism seen in pseudorotation of disphenoidal molecules, and a "turnstile" mechanism (which can be seen in trigonal bipyramidal molecules under certain conditions). References[edit]^ WJ Adams, HB Thompson, LS Bartell, 1970, J. Chem. Phys. 53:4040-6. ^ LS Bartell, MJ Rothman & A Gavezzotti, 1982, , J. Chem
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Berry Mechanism
The Berry mechanism, or Berry pseudorotation mechanism, is a type of vibration causing molecules of certain geometries to isomerize by exchanging the two axial ligands (see Figure at right) for two of the equatorial ones. It is the most widely accepted mechanism for pseudorotation. It most commonly occurs in trigonal bipyramidal molecules, such as PF5, though it can also occur in molecules with a square pyramidal geometry
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Molecular Vibration
A molecular vibration occurs when atoms in a molecule are in periodic motion while the molecule as a whole has constant translational and rotational motion. The frequency of the periodic motion is known as a vibration frequency, and the typical frequencies of molecular vibrations range from less than 1013 to approximately 1014 Hz, corresponding to wavenumbers of approximately 300 to 3000 cm−1. In general, a molecule with N atoms has 3N – 6 normal modes of vibration, but a linear molecule has 3N – 5 such modes, because rotation about its molecular axis cannot be observed.[1] A diatomic molecule has one normal mode of vibration
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Alkane
In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon-carbon bonds are single.[1] Alkanes have the general chemical formula CnH2n+2. The alkanes range in complexity from the simplest case of methane, CH4 where n = 1 (sometimes called the parent molecule), to arbitrarily large molecules. Besides this standard definition by the International Union of Pure and Applied Chemistry, in some authors' usage the term alkane is applied to any saturated hydrocarbon, including those that are either monocyclic (i.e. the cycloalkanes) or polycyclic.[2] In an alkane, each carbon atom has 4 bonds (either C-C or C-H), and each hydrogen atom is joined to one of the carbon atoms (so in a C-H bond)
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Eclipsed Conformation
In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°.[1] Such a conformation exists in any open chain, single chemical bond connecting two sp3-hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance, but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms). In the example of ethane in Newman projection
Newman projection
it shows that rotation around the carbon-carbon bond is not entirely free but that an energy barrier exists
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