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Alkene
In organic chemistry , an ALKENE is an unsaturated hydrocarbon that contains at least one carbon –carbon double bond . The words alkene and olefin are often used interchangeably (see nomenclature section below). Acyclic alkenes, with only one double bond and no other functional groups , known as mono-enes, form a homologous series of hydrocarbons with the general formula C nH 2n. Alkenes have two hydrogen atoms fewer than the corresponding alkane (with the same number of carbon atoms). The simplest alkene, ethylene (C2H4), with the International Union of Pure and Applied Chemistry (IUPAC) name ethene, is the organic compound produced on the largest scale industrially. Aromatic
Aromatic
compounds are often drawn as cyclic alkenes, but their structure and properties are different and they are not considered to be alkenes
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E-Z Notation
E-Z CONFIGURATION, or the E-Z CONVENTION, is the IUPAC
IUPAC
preferred method of describing the absolute stereochemistry of double bonds in organic chemistry . It is an extension of cis/trans notation (which only describes relative stereochemistry) that can be used to describe double bonds having two, three or four substituents . Following the Cahn–Ingold–Prelog priority rules (CIP rules), each substituent on a double bond is assigned a priority. If the two groups of higher priority are on opposite sides of the double bond, the bond is assigned the configuration E (from entgegen, German: , the German word for "opposite"). If the two groups of higher priority are on the same side of the double bond, the bond is assigned the configuration Z (from zusammen, German: , the German word for "together")
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Pyramidalization
In chemistry , TRIGONAL PLANAR is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle , called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to the point group D3h . Molecules where the three ligands are not identical, such as H2CO , deviate from this idealized geometry. Examples of molecules with trigonal planar geometry include boron trifluoride (BF3), formaldehyde (H2CO), phosgene (COCl2), and sulfur trioxide (SO3). Some ions with trigonal planar geometry include nitrate (NO− 3), carbonate (CO2− 3), and guanidinium (C(NH 2)+ 3). In organic chemistry, planar, three-connected carbon centers that are trigonal planar are often described as having sp2 hybridization . Nitrogen inversion is the distortion of pyramidal amines through a transition state that is trigonal planar
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Dihedral Angle
A DIHEDRAL ANGLE is the angle between two intersecting planes. In chemistry it is the angle between planes through two sets of three atoms, having two atoms in common. In solid geometry it is defined as the union of a line and two half-planes that have this line as a common edge . In higher dimension, a dihedral angle represents the angle between two hyperplanes . CONTENTS * 1 Definitions * 2 Dihedral angles in stereochemistry * 3 Dihedral angles of proteins * 3.1 Converting from dihedral angles to Cartesian coordinates in chains * 4 Calculation of a dihedral angle * 5 Dihedral angles in polyhedra * 6 See also * 7 References * 8 External links DEFINITIONSA dihedral angle is an angle between two intersecting planes on a third plane perpendicular to the line of intersection
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Isomer
An ISOMER (/ˈaɪsəmər/ ; from Greek ἰσομερής, isomerès; isos = "equal", méros = "part") is a molecule with the same molecular formula as another molecule, but with a different chemical structure . That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms. Isomers do not necessarily share similar properties, unless they also have the same functional groups . There are two main forms of ISOMERISM (/ˈaɪsəmərɪzm/ or /aɪˈsɒmərɪzm/ ): structural isomerism (or constitutional isomerism) and stereoisomerism (or spatial isomerism)
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Orbital Hybridization
In chemistry , HYBRIDISATION (or HYBRIDIZATION ) is the concept of mixing atomic orbitals into new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals) suitable for the pairing of electrons to form chemical bonds in valence bond theory . Hybrid orbitals are very useful in the explanation of molecular geometry and atomic bonding properties. Although sometimes taught together with the valence shell electron-pair repulsion (VSEPR) theory , valence bond and hybridisation are in fact not related to the VSEPR model
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Mole (unit)
The MOLE is the unit of measurement in the International System of Units (SI) for amount of substance . The unit is defined as the amount of a chemical substance that contains as many representative particles, e.g., atoms , molecules , ions , electrons , or photons , as there are atoms in 12 grams of carbon-12 (12C), the isotope of carbon with standard atomic weight 12 by definition. This number is expressed by the Avogadro constant
Avogadro constant
, which has a value of 7023602214085700000♠6.022140857×1023 mol−1, which is just over 602 sextillion (thousand million million million ). The mole is one of the base units of the SI, and has the unit symbol MOL. The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 → 2 H2O implies that 2 moles of dihydrogen (H2) and 1 mole of dioxygen (O2) react to form 2 moles of water (H2O)
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Ångström
The åNGSTRöM (/ˈæŋstrəm, -strʌm/ , ANG-strəm ; ANG-strum Swedish: ) or ANGSTROM is a unit of length equal to 6990100000000000000♠10−10 m (one ten-billionth of a metre ) or 0.1 nanometre . Its symbol is Å , a letter in the Swedish alphabet . The natural sciences and technology often use ångström to express sizes of atoms , molecules , microscopic biological structures, and lengths of chemical bonds , arrangement of atoms in crystals , wavelengths of electromagnetic radiation , and dimensions of integrated circuit parts. Atoms of phosphorus, sulfur, and chlorine are about an ångström in covalent radius, while a hydrogen atom is about half an ångström; see atomic radius . Visible light has wavelengths in the range of 4000–7000 Å. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–1874). The symbol is always written with a ring diacritic , as the letter in the Swedish alphabet
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Picometre
The PICOMETRE (International spelling as used by the International Bureau of Weights and Measures ; SI symbol: PM) or PICOMETER (American spelling ) is a unit of length in the metric system , equal to 6988100000000000000♠1×10−12 m , or one trillionth (1/7012100000000000000♠1000000000000) of a metre , which is the SI base unit of length. The picometre is one thousandth of a nanometre , one millionth of a micrometre (also known as a micron), and used to be called micromicron, stigma, or bicron. The symbol µµ was once used for it. It is also one hundredth of an angstrom , an internationally recognised (but non-SI) unit of length. USEThe picometre's length is of an order such that its application is almost entirely confined to particle physics , quantum physics , chemistry and acoustics
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VSEPR Theory
VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR) THEORY is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie -Nyholm theory after its two main developers. The acronym "VSEPR" is pronounced either "ves-pur" :410 or "vuh-seh-per". The premise of VSEPR is that the valence electron pairs surrounding an atom tend to repel each other and will, therefore, adopt an arrangement that minimizes this repulsion, thus determining the molecule's geometry . Gillespie has emphasized that the electron-electron repulsion due to the Pauli exclusion principle
Pauli exclusion principle
is more important in determining molecular geometry than the electrostatic repulsion
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Electron
The ELECTRON is a subatomic particle , symbol e− or β− , with a negative elementary electric charge . Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton . Quantum mechanical properties of the electron include an intrinsic angular momentum (spin ) of a half-integer value, expressed in units of the reduced Planck constant , ħ. As it is a fermion , no two electrons can occupy the same quantum state , in accordance with the Pauli exclusion principle . Like all elementary particles, electrons exhibit properties of both particles and waves : they can collide with other particles and can be diffracted like light
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Physical State
In physics , a STATE OF MATTER is one of the distinct forms that matter takes on. Four states of matter are observable in everyday life: solid , liquid , gas , and plasma . Many other states are known to exist only in extreme situations, such as Bose–Einstein condensates , neutron-degenerate matter , and quark-gluon plasma , which only occur in situations of extreme cold, extreme density, and extremely high-energy color-charged matter respectively. Some other states are believed to be possible but remain theoretical for now. For a complete list of all exotic states of matter, see the list of states of matter . Historically, the distinction is made based on qualitative differences in properties. Matter
Matter
in the solid state maintains a fixed volume and shape, with component particles (atoms , molecules or ions ) close together and fixed into place
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Molecular Mass
MOLECULAR MASS or MOLECULAR WEIGHT is the mass of a molecule . It is calculated as the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element in the molecular formula . The molecular mass of small to medium size molecules, measured by mass spectrometry, determines stoichiometry . For large molecules such as proteins , methods based on viscosity and light-scattering can be used to determine molecular mass when crystallographic data are not available. CONTENTS * 1 Definitions * 2 Determination * 2.1 Mass spectrometry
Mass spectrometry
* 2.2 Hydrodynamic methods * 2.3 Static light scattering * 3 See also * 4 References * 5 External links DEFINITIONSBoth atomic and molecular masses are usually obtained relative to the mass of the isotope 12C (carbon 12), which by definition is equal to 12
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Electrophilic Addition
In organic chemistry , an ELECTROPHILIC ADDITION reaction is an addition reaction where, in a chemical compound , a π bond is broken and two new σ bonds are formed. The substrate of an electrophilic addition reaction must have a double bond or triple bond . The driving force for this reaction is the formation of an electrophile X+ that forms a covalent bond with an electron-rich unsaturated C=C bond. The positive charge on X is transferred to the carbon-carbon bond, forming a carbocation during the formation of the C-X bond. In step 2 of an electrophilic addition, the positively charged intermediate combines with (Y) that is electron-rich and usually an anion to form the second covalent bond. Step 2 is the same nucleophilic attack process found in an SN1 reaction . The exact nature of the electrophile and the nature of the positively charged intermediate are not always clear and depend on reactants and reaction conditions
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Bredt's Rule
BREDT\'S RULE is an empirical observation in organic chemistry that states that a double bond cannot be placed at the bridgehead of a bridged ring system, unless the rings are large enough. The rule is named after Julius Bredt
Julius Bredt
, who first discussed it in 1902 and codified it in 1924. It primarily relates to bridgeheads with carbon-carbon and carbon-nitrogen double bonds. For example, two of the following isomers of norbornene violate Bredt's rule, which makes them too unstable to prepare: In the figure, the bridgehead atoms involved in Bredt's rule violation are highlighted in red
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Nonbonded Interactions
INTERMOLECULAR FORCES (IMFs) are the forces which mediate interaction between molecules , including forces of attraction or repulsion which act between molecules and other types of neighboring particles, e.g., atoms or ions . Inter-molecular forces are weak relative to intramolecular forces – the forces which hold a molecule together. For example, the covalent bond , involving sharing electron pairs between atoms, is much stronger than the forces present between neighboring molecules. Both sets of forces are essential parts of force fields frequently used in molecular mechanics . The investigation of inter-molecular forces starts from macroscopic observations which indicate the existence and action of forces at a molecular level. These observations include non-ideal-gas thermodynamic behavior reflected by virial coefficients , vapor pressure , viscosity , superficial tension, and absorption data
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