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SNi Reaction
In chemistry, Si (substitution nucleophilic internal) refers to a specific, regio-selective but not often encountered reaction mechanism for nucleophilic aliphatic substitution. The name was introduced by Cowdrey et al. in 1937 to label nucleophilic reactions which occur with retention of configuration, but later was employed to describe various reactions that proceed with a similar mechanism. A typical representative organic reaction displaying this mechanism is the chlorination of alcohols with thionyl chloride, or the decomposition of alkyl chloroformates, the main feature is retention of stereochemical configuration. Some examples for this reaction were reported by Edward S. Lewis and Charles E. Boozer in 1952. Mechanistic and kinetic studies were reported few years later by various researchers. Thionyl chloride first reacts with the alcohol to form an alkyl chloro sulfite, actually forming an intimate ion pair. The second step is the loss of a sulfur dioxide molecule an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during chemical reaction, reactions with other chemical substance, substances. Chemistry also addresses the nature of chemical bonds in chemical compounds. In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both Basic research, basic and Applied science, applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the prop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. It is a common element in the universe, estimated at Abundance of the chemical elements, seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element chemical bond, bond to form N2, a colourless and odourless diatomic molecule, diatomic gas. N2 forms about 78% of Atmosphere of Earth, Earth's atmosphere, making it the most abundant chemical species in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772 and independently by Carl Wilhelm Scheele and Henry Cavendish at about the same time. The name was suggested by French chemist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic Acyl Substitution
In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an organyl group () or hydrogen in the case of formyl group (). In organic chemistry, the acyl group (IUPAC name alkanoyl if the organyl group is alkyl) is usually derived from a carboxylic acid, in which case it has the formula , where R represents an organyl group or hydrogen. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids and phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond. Reactivity trends There are five main types of acyl derivatives. Acid halides are the most reactive towards nucleophiles, followed by anhydrides, esters, and amides. Carboxylate ions are esse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SNi Reaction Mechanism
In chemistry, Si (substitution nucleophilic internal) refers to a specific, regio-selective but not often encountered reaction mechanism for nucleophilic aliphatic substitution. The name was introduced by Cowdrey et al. in 1937 to label nucleophilic reactions which occur with retention of configuration, but later was employed to describe various reactions that proceed with a similar mechanism. A typical representative organic reaction displaying this mechanism is the chlorination of alcohols with thionyl chloride, or the decomposition of alkyl chloroformates, the main feature is retention of stereochemical configuration. Some examples for this reaction were reported by Edward S. Lewis and Charles E. Boozer in 1952. Mechanistic and kinetic studies were reported few years later by various researchers. Thionyl chloride first reacts with the alcohol to form an alkyl chloro sulfite, actually forming an intimate ion pair. The second step is the loss of a sulfur dioxide molecule an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged Atomic nucleus, atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as Alcohol (chemistry), alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. The difference between the two is, that basicity is a thermodynamic property (i.e. relates to an equilibrium state), but nucleop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SN2 Reaction
The bimolecular nucleophilic substitution (SN2) is a type of reaction mechanism that is common in organic chemistry. In the SN2 reaction, a strong nucleophile forms a new bond to an sp3-hybridised carbon atom via a backside attack, all while the leaving group detaches from the reaction center in a concerted (i.e. simultaneous) fashion. The name SN2 refers to the Hughes-Ingold symbol of the mechanism: "SN" indicates that the reaction is a nucleophilic substitution, and "2" that it proceeds via a bimolecular mechanism, which means both the reacting species are involved in the rate-determining step. What distinguishes SN2 from the other major type of nucleophilic substitution, the SN1 reaction, is that the displacement of the leaving group, which is the rate-determining step, is separate from the nucleophilic attack in SN1. The SN2 reaction can be considered as an organic-chemistry analogue of the associative substitution from the field of inorganic chemistry. Reaction mech ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Walden Inversion
Walden inversion is the inversion of a stereogenic center in a chiral molecule in a chemical reaction. Since a molecule can form two enantiomers around a stereogenic center, the Walden inversion converts the configuration of the molecule from one enantiomeric form to the other. For example, in an SN2 reaction, Walden inversion occurs at a tetrahedral carbon atom. It can be visualized by imagining an umbrella turned inside-out in a gale. In the Walden inversion, the backside attack by the nucleophile in an SN2 reaction gives rise to a product whose configuration is opposite to the reactant. Therefore, during SN2 reaction, 100% inversion of product takes place. This is known as Walden inversion. It was first observed by chemist Paul Walden in 1896. He was able to convert one enantiomer of a chemical compound into the other enantiomer and back again in a so-called Walden cycle which went like this: (+)- chlorosuccinic acid (1 in the illustration) was converted to (+)-malic ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow, due to the formation of extended, unsaturated Polymer, polymeric chains, which show significant electrical conductivity. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. As of 2016, it is synthesized on the scale of about 20,000 tons per year worldwide. Properties Physical properties Pyridine is diamagnetism, diamagnetic. Its critical point (thermodynamics), critical parameters are: pressure 5.63 MPa, temperature 619 K and volume 248 cm3/mol. In the temperatur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reactive Intermediate
In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these compounds be isolated and stored, e.g. low temperatures, matrix isolation. When their existence is indicated, reactive intermediates can help explain how a chemical reaction takes place. Most chemical reactions take more than one elementary step to complete, and a reactive intermediate is a high-energy, hence unstable, product that exists only in one of the intermediate steps. The series of steps together make a reaction mechanism. A reactive intermediate differs from a reactant or product or a simple reaction intermediate only in that it cannot usually be isolated but is sometimes observable only through fast spectroscopic methods. It is stable in the sense that an elementary reaction forms the reactive intermediate and the elementary rea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cation
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons. A cation is a positively charged ion with fewer electrons than protons (e.g. K+ ( potassium ion)) while an anion is a negatively charged ion with more electrons than protons (e.g. Cl− ( chloride ion) and OH− ( hydroxide ion)). Opposite electric charges are pulled towards one another by electrostatic force, so cations and anions attract each other and readily form ionic compounds. Ions consisting of only a single atom are termed ''monatomic ions'', ''atomic ions'' or ''simple ions'', while ions consisting of two or more atoms are termed polyatomic ions or ''molecular ions''. If only a + or − is present, it indic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitrogen Mustard
Nitrogen mustards (NMs) are cytotoxic organic compounds with the bis(2-chloroethyl)amino ((ClC2H4)2NR) functional group. Although originally produced as chemical warfare agents, they were the first chemotherapeutic agents for treatment of cancer. Nitrogen mustards are nonspecific DNA alkylating agents. Name Nitrogen mustards are not related to the mustard plant or its pungent essence, allyl isothiocyanate; the name comes from the pungent smell of chemical weapons preparations. Chemical warfare During World War II, nitrogen mustards were studied at the Yale School of Medicine by Alfred Gilman and Louis Goodman, and in December 1942, they started classified human clinical trials of nitrogen mustards for the treatment of lymphoma. In early December of 1943, an incident during the air raid on Bari, Italy, led to the release of mustard gas that affected several hundred soldiers and civilians. Medical examination of the survivors showed a decreased number of lymphocytes. Aft ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
