|
Polarizable Continuum Model
The polarizable continuum model (PCM) is a commonly used method in computational chemistry to model solvation effects. If it is necessary to consider each solvent molecule as a separate molecule, the computational cost of modeling a solvent-mediated chemical reaction would grow prohibitively high. Modeling the solvent as a polarizable continuum, rather than individual molecules, makes ''ab initio'' computation feasible. Two types of PCMs have been popularly used: the dielectric PCM (D-PCM) in which the continuum is polarizable (see dielectrics) and the conductor-like PCM (C-PCM) in which the continuum is conductor-like similar to COSMO Solvation Model.Jacopo Tomasi, Benedetta Mennucci, and Roberto Cammi (2005). "Quantum Mechanical Continuum Solvation Models." Chem. Rev. 105(8): 2999-309/ref> The molecular Gibbs free energy, free energy of solvation is computed as the sum of three terms: :''G''sol = ''G''es + ''G''dr + ''G''cav ::''G''es = electrostatic ::''G''dr = dispersion-re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computational Chemistry
Computational chemistry is a branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into computer programs, to calculate the structures and properties of molecules, groups of molecules, and solids. It is essential because, apart from relatively recent results concerning the hydrogen molecular ion (dihydrogen cation, see references therein for more details), the quantum many-body problem cannot be solved analytically, much less in closed form. While computational results normally complement the information obtained by chemical experiments, it can in some cases predict hitherto unobserved chemical phenomena. It is widely used in the design of new drugs and materials. Examples of such properties are structure (i.e., the expected positions of the constituent atoms), absolute and relative (interaction) energies, electronic charge density distributions, dipoles and higher multipole moments, vi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gaussian (software)
Gaussian is a general purpose computational chemistry software package initially released in 1970 by John Pople and his research group at Carnegie Mellon University as Gaussian 70. It has been continuously updated since then. The name originates from Pople's use of Gaussian orbitals to speed up molecular electronic structure calculations as opposed to using Slater-type orbitals, a choice made to improve performance on the limited computing capacities of then-current computer hardware for Hartree–Fock calculations. The current version of the program is Gaussian 16. Originally available through the Quantum Chemistry Program Exchange, it was later licensed out of Carnegie Mellon University, and since 1987 has been developed and licensed by Gaussian, Inc. Standard abilities According to the most recent Gaussian manual, the package can do: *Molecular mechanics **AMBER **Universal force field (UFF) **DREIDING force field *Semi-empirical quantum chemistry method calculations **Austin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline. It is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. Although benzene is a major industrial chemical, it finds limited use in consumer items because of its toxicity. History Discovery The word "''benzene''" derives from "''gum benzoin''" (benzoin res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Tetrachloride
Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVACR) is an organic compound with the chemical formula CCl4. It is a colourless liquid with a "sweet" smell that can be detected at low levels. It is practically incombustible at lower temperatures. It was formerly widely used in fire extinguishers, as a precursor to refrigerants and as a cleaning agent, but has since been phased out because of environmental and safety concerns. Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system and degenerate the liver and kidneys. Prolonged exposure can be fatal. Properties In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedron, tetrahedral configuration joined to a central carbon atom by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetonitrile
Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not classed as organic). It is produced mainly as a byproduct of acrylonitrile manufacture. It is used as a polar aprotic solvent in organic synthesis and in the purification of butadiene. The skeleton is linear with a short distance of 1.16 Å. Acetonitrile was first prepared in 1847 by the French chemist Jean-Baptiste Dumas. Applications Acetonitrile is used mainly as a solvent in the purification of butadiene in refineries. Specifically, acetonitrile is fed into the top of a distillation column filled with hydrocarbons including butadiene, and as the acetonitrile falls down through the column, it absorbs the butadiene which is then sent from the bottom of the tower to a second separating tower. Heat is then employed in the separatin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a light, volatile, colourless, flammable liquid with a distinctive alcoholic odour similar to that of ethanol (potable alcohol). A polar solvent, methanol acquired the name wood alcohol because it was once produced chiefly by the destructive distillation of wood. Today, methanol is mainly produced industrially by hydrogenation of carbon monoxide. Methanol consists of a methyl group linked to a polar hydroxyl group. With more than 20 million tons produced annually, it is used as a precursor to other commodity chemicals, including formaldehyde, acetic acid, methyl tert-butyl ether, methyl benzoate, anisole, peroxyacids, as well as a host of more specialised chemicals. Occurrence Small amounts of methanol are present in normal, healthy hu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible with water and serves as an important organic solvent in its own right, in industry, home, and laboratory. About 6.7 million tonnes were produced worldwide in 2010, mainly for use as a solvent and production of methyl methacrylate (and from that PMMA) as well as bisphenol A.Acetone World Petrochemicals report, January 2010Stylianos Sifniades, Alan B. Levy, "Acetone" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. It is a common building block in |
Cyclohexane
Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colorless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohexane is mainly used for the industrial production of adipic acid and caprolactam, which are precursors to nylon. Cyclohexyl () is the alkyl substituent of cyclohexane and is abbreviated Cy. Production Modern On an industrial scale, cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel catalyst. Producers of cyclohexane account for approximately 11.4% of global demand for benzene. The reaction is highly exothermic, with ΔH(500 K) = -216.37 kJ/mol. Dehydrogenation commenced noticeably above 300 °C, reflecting the favorable entropy for dehydrogenation. : Early Unlike benzene, cyclohexane is not found in natural resources such as coal. For this reason, early investigators synthesized their cyclohexane ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GAMESS
GAMESS is a computational chemistry software program and stands for General Atomic and Molecular Electronic Structure System. The original Quantum Chemistry Program Exchange (QCPE) code of GAMESS split in 1981 and now the three version differ considerably: * GAMESS (UK), a fork of the General Atomic and Molecular Electronic Structure System computational chemistry software program * GAMESS (US), a fork of the General Atomic and Molecular Electronic Structure System computational chemistry software program * Firefly (computer program) Firefly, formerly named PC GAMESS, is an ab initio computational chemistry program for Intel-compatible x86, x86-64 processors based on GAMESS (US) sources. However, it has been mostly rewritten (60-70% of the code), especially in platform-spe ... or PC GAMESS, an ab initio computational chemistry program based on GAMESS (US) sources Computational chemistry software {{chem-software-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Density Functional Theory
Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases. Using this theory, the properties of a many-electron system can be determined by using functionals, i.e. functions of another function. In the case of DFT, these are functionals of the spatially dependent electron density. DFT is among the most popular and versatile methods available in condensed-matter physics, computational physics, and computational chemistry. DFT has been very popular for calculations in solid-state physics since the 1970s. However, DFT was not considered accurate enough for calculations in quantum chemistry until the 1990s, when the approximations used in the theory were greatly refined to better model the exchange and correlation interactions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvation
Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding, and van der Waals forces. Solvation of a solute by water is called hydration. Solubility of solid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2.png "Click for more on -> Benzene")
