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37-542: [REDACTED] Look up elimination in Wiktionary, the free dictionary. Elimination may refer to: Science and medicine [ edit ] Elimination reaction , an organic reaction in which two functional groups split to form an organic product Bodily waste elimination, discharging feces , urine , or foreign substances from the body via defecation , urination , and emesis Drug elimination, clearance of

74-411: A "bond" is a shared pair of electrons (the other method of bonding between atoms is called ionic bonding and involves a positive cation and a negative anion ). Molecular geometries can be specified in terms of 'bond lengths', 'bond angles' and 'torsional angles'. The bond length is defined to be the average distance between the nuclei of two atoms bonded together in any given molecule. A bond angle

111-414: A 1989 single from Overkill's album The Years of Decay Accounting [ edit ] Elimination (accounting) , the act of recording amounts in a consolidation statement to remove the effects of inter-company transactions See also [ edit ] Eliminator (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

148-691: A 3° haloalkane is reacts with an alkoxide, due to strong basic character of the alkoxide and unreactivity of 3° group towards S N 2, only alkene formation by E2 elimination is observed. Thus, elimination by E2 limits the scope of the Williamson ether synthesis (an S N 2 reaction) to essentially only 1° haloalkanes; 2° haloalkanes generally do not give synthetically useful yields, while 3° haloalkanes fail completely. With strong base, 3° haloalkanes give elimination by E2. With weak bases, mixtures of elimination and substitution products form by competing S N 1 and E1 pathways. The case of 2° haloalkanes

185-411: A drug or other foreign agent from the body Elimination, the destruction of an infectious disease in one region of the world as opposed to its eradication from the entire world Hazard elimination , the most effective type of hazard control Elimination (pharmacology) , processes by which a drug is eliminated from an organism Logic and mathematics [ edit ] Elimination theory ,

222-408: A gas. The position of each atom is determined by the nature of the chemical bonds by which it is connected to its neighboring atoms. The molecular geometry can be described by the positions of these atoms in space, evoking bond lengths of two joined atoms, bond angles of three connected atoms, and torsion angles ( dihedral angles ) of three consecutive bonds. Since the motions of the atoms in

259-435: A knock-out style of tournament competition Elimination (arcade game) , 1974 arcade game by Atari Inc. subsidiary Key Games Elimination, a variant of the "lifestyle-invading" game Assassin , played with clothes-pins Elimination from postseason contention in a sports league Music [ edit ] Elimination , a 2002 album by Deceptikonz Elimination (Jughead's Revenge album) , 1994 "Elimination",

296-455: A metal-carbene complex. In these reactions, it is the carbon adjacent to the metal that undergoes α-elimination.) In certain special cases, γ- and higher eliminations to form three-membered or larger rings is also possible in both organic and organometallic processes. For instance, certain Pt(II) complexes undergo γ- and δ-elimination to give metallocycles. More recently, γ-silyl elimination of

333-414: A molecule are determined by quantum mechanics, "motion" must be defined in a quantum mechanical way. The overall (external) quantum mechanical motions translation and rotation hardly change the geometry of the molecule. (To some extent rotation influences the geometry via Coriolis forces and centrifugal distortion , but this is negligible for the present discussion.) In addition to translation and rotation,

370-498: A one-step mechanism in which carbon-hydrogen and carbon-halogen bonds break to form a double bond ( C=C Pi bond ). The specifics of the reaction are as follows: An example of this type of reaction in scheme 1 is the reaction of isobutylbromide with potassium ethoxide in ethanol . The reaction products are isobutene , ethanol and potassium bromide . E1 is a model to explain a particular type of chemical elimination reaction. E1 stands for unimolecular elimination and has

407-505: A silylcyclobutyl tosylate has been used to prepare strained bicyclic systems. Many of the concepts and terminology related to elimination reactions were proposed by Christopher Kelk Ingold in the 1920s. Molecular geometry Molecular geometry is the three-dimensional arrangement of the atoms that constitute a molecule . It includes the general shape of the molecule as well as bond lengths , bond angles , torsional angles and any other geometrical parameters that determine

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444-446: A third type of motion is molecular vibration , which corresponds to internal motions of the atoms such as bond stretching and bond angle variation. The molecular vibrations are harmonic (at least to good approximation), and the atoms oscillate about their equilibrium positions, even at the absolute zero of temperature. At absolute zero all atoms are in their vibrational ground state and show zero point quantum mechanical motion , so that

481-425: Is an energy unit that is commonly used in infrared spectroscopy ; 1 cm corresponds to 1.239 84 × 10  eV ). When an excitation energy is 500 cm , then about 8.9 percent of the molecules are thermally excited at room temperature. To put this in perspective: the lowest excitation vibrational energy in water is the bending mode (about 1600 cm ). Thus, at room temperature less than 0.07 percent of all

518-401: Is not a good leaving group, so eliminations with fluoride as the leaving group have slower rates than other halogens . There is a certain level of competition between the elimination reaction and nucleophilic substitution . More precisely, there are competitions between E2 and S N 2 and also between E1 and S N 1 . Generally, elimination is favored over substitution when For example, when

555-452: Is relatively complex. For strongly basic nucleophiles (p K aH > 11, e.g., hydroxide, alkoxide, acetylide), the result is generally elimination by E2, while weaker bases that are still good nucleophiles (e.g., acetate, azide, cyanide, iodide) will give primarily S N 2. Finally, weakly nucleophilic species (e.g., water, alcohols, carboxylic acids) will give a mixture of S N 1 and E1. For 1° haloalkanes with β-branching, E2 elimination

592-535: Is still generally preferred over S N 2 for strongly basic nucleophiles. Unhindered 1° haloalkanes favor S N 2 when the nucleophile is also unhindered. However, strongly basic and hindered nucleophiles favor E2. In general, with the exception of reactions in which E2 is impossible because β hydrogens are unavailable (e.g. methyl, allyl, and benzyl halides), clean S N 2 substitution is hard to achieve when strong bases are used, as alkene products arising from elimination are almost always observed to some degree. On

629-466: Is the angle formed between three atoms across at least two bonds. For four atoms bonded together in a chain, the torsional angle is the angle between the plane formed by the first three atoms and the plane formed by the last three atoms. There exists a mathematical relationship among the bond angles for one central atom and four peripheral atoms (labeled 1 through 4) expressed by the following determinant. This constraint removes one degree of freedom from

666-451: Is α-elimination. For a carbon center, the result of α-elimination is the formation of a carbene, which includes "stable carbenes" such as carbon monoxide or isocyanides . For instance, α-elimination the elements of HCl from chloroform (CHCl 3 ) in the presence of strong base is a classic approach for the generation of dichlorocarbene , :CCl 2 , as a reactive intermediate. On the other hand, formic acid undergoes α-elimination to afford

703-453: The choices of (originally) six free bond angles to leave only five choices of bond angles. (The angles θ 11 , θ 22 , θ 33 , and θ 44 are always zero and that this relationship can be modified for a different number of peripheral atoms by expanding/contracting the square matrix.) Molecular geometry is determined by the quantum mechanical behavior of the electrons. Using the valence bond approximation this can be understood by

740-416: The electrons are delocalised. An understanding of the wavelike behavior of electrons in atoms and molecules is the subject of quantum chemistry . Isomers are types of molecules that share a chemical formula but have difference geometries, resulting in different properties: A bond angle is the geometric angle between two adjacent bonds. Some common shapes of simple molecules include: The bond angles in

777-546: The ethyl (0.99) and isopropyl (1.72) analogues suggest competition between the two reaction modes. β-Elimination, with loss of electrofuge and nucleofuge on vicinal carbon atoms, is by far the most common type of elimination. The ability to form a stable product containing a C=C or C=X bond, as well as orbital alignment considerations, strongly favors β-elimination over other elimination processes. However, other types are known, generally for systems where β-elimination cannot occur. The next most common type of elimination reaction

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814-504: The following specifications An example in scheme 2 is the reaction of tert-butylbromide with potassium ethoxide in ethanol. E1 eliminations happen with highly substituted alkyl halides for two main reasons. If S N 1 and E1 pathways are competing, the E1 pathway can be favored by increasing the heat. Specific features : The reaction rate is influenced by the reactivity of halogens , iodide and bromide being favored. Fluoride

851-400: The molecular structure is averaged over more accessible geometries (see next section). Larger molecules often exist in multiple stable geometries ( conformational isomerism ) that are close in energy on the potential energy surface . Geometries can also be computed by ab initio quantum chemistry methods to high accuracy. The molecular geometry can be different as a solid, in solution, and as

888-638: The molecule geometry from the details of the vibrational and rotational absorbance detected by these techniques. X-ray crystallography , neutron diffraction and electron diffraction can give molecular structure for crystalline solids based on the distance between nuclei and concentration of electron density. Gas electron diffraction can be used for small molecules in the gas phase. NMR and FRET methods can be used to determine complementary information including relative distances, dihedral angles, angles, and connectivity. Molecular geometries are best determined at low temperature because at higher temperatures

925-640: The molecules of a given amount of water will vibrate faster than at absolute zero. As stated above, rotation hardly influences the molecular geometry. But, as a quantum mechanical motion, it is thermally excited at relatively (as compared to vibration) low temperatures. From a classical point of view it can be stated that at higher temperatures more molecules will rotate faster, which implies that they have higher angular velocity and angular momentum . In quantum mechanical language: more eigenstates of higher angular momentum become thermally populated with rising temperatures. Typical rotational excitation energies are on

962-697: The order of a few cm . The results of many spectroscopic experiments are broadened because they involve an averaging over rotational states. It is often difficult to extract geometries from spectra at high temperatures, because the number of rotational states probed in the experimental averaging increases with increasing temperature. Thus, many spectroscopic observations can only be expected to yield reliable molecular geometries at temperatures close to absolute zero, because at higher temperatures too many higher rotational states are thermally populated. Molecules, by definition, are most often held together with covalent bonds involving single, double, and/or triple bonds, where

999-400: The other hand, clean E2 can be achieved by simply selecting a sterically hindered base (e.g., potassium tert -butoxide). Similarly, attempts to effect substitution by S N 1 almost always result in a product mixture contaminated by some E1 product (again, with the exception of cases where the lack of β hydrogens makes elimination impossible). In one study the kinetic isotope effect (KIE)

1036-553: The position of each atom. Molecular geometry influences several properties of a substance including its reactivity , polarity , phase of matter , color , magnetism and biological activity . The angles between bonds that an atom forms depend only weakly on the rest of molecule, i.e. they can be understood as approximately local and hence transferable properties . The molecular geometry can be determined by various spectroscopic methods and diffraction methods. IR , microwave and Raman spectroscopy can give information about

1073-563: The recognizable geometry of the molecule. To get a feeling for the probability that the vibration of molecule may be thermally excited, we inspect the Boltzmann factor β ≡ exp(− ⁠ Δ E / kT ⁠ ) , where Δ E is the excitation energy of the vibrational mode, k the Boltzmann constant and T the absolute temperature. At 298 K (25 °C), typical values for the Boltzmann factor β are: (The reciprocal centimeter

1110-426: The stable products water and carbon monoxide under acidic conditions. α-Elimination may also occur on a metal center, one particularly common result of which is lowering of both the metal oxidation state and coordination number by 2 units in a process known as reductive elimination . (Confusingly, in organometallic terminology, the terms α-elimination and α-abstraction refer to processes that result in formation of

1147-402: The table below are ideal angles from the simple VSEPR theory (pronounced "Vesper Theory") , followed by the actual angle for the example given in the following column where this differs. For many cases, such as trigonal pyramidal and bent, the actual angle for the example differs from the ideal angle, and examples differ by different amounts. For example, the angle in H 2 S (92°) differs from

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1184-400: The tetrahedral angle by much more than the angle for H 2 O (104.48°) does. Molecule Art is a relatively obscure form of abstract art in which Molecular Geometry, most often a skeletal formation. The greater the amount of lone pairs contained in a molecule, the smaller the angles between the atoms of that molecule. The VSEPR theory predicts that lone pairs repel each other, thus pushing

1221-480: The theory of the methods to eliminate variables between polynomial equations. Disjunctive syllogism , a rule of inference Gaussian elimination , a method of solving systems of linear equations Fourier–Motzkin elimination , an algorithm for reducing systems of linear inequalities Process of elimination , enumerating all answers and discarding each unfit answer Variable elimination Games and competitions [ edit ] Elimination tournament ,

1258-535: The title Elimination . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Elimination&oldid=1114262730 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Elimination reaction The E2 mechanism, where E2 stands for bimolecular elimination , involves

1295-457: The type of bonds between the atoms that make up the molecule. When atoms interact to form a chemical bond , the atomic orbitals of each atom are said to combine in a process called orbital hybridisation . The two most common types of bonds are sigma bonds (usually formed by hybrid orbitals) and pi bonds (formed by unhybridized p orbitals for atoms of main group elements ). The geometry can also be understood by molecular orbital theory where

1332-416: The wavefunction of a single vibrational mode is not a sharp peak, but approximately a Gaussian function (the wavefunction for n  = 0 depicted in the article on the quantum harmonic oscillator ). At higher temperatures the vibrational modes may be thermally excited (in a classical interpretation one expresses this by stating that "the molecules will vibrate faster"), but they oscillate still around

1369-456: Was determined for the gas phase reaction of several alkyl halides with the chlorate ion. In accordance with an E2 elimination the reaction with t-butyl chloride results in a KIE of 2.3. The methyl chloride reaction (only S N 2 possible) on the other hand has a KIE of 0.85 consistent with a S N 2 reaction because in this reaction type the C-H bonds tighten in the transition state. The KIE's for

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