|
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 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 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. History The terms ''nucleophile'' and ''electrophile'' were introduced by Christopher Kelk Ingold in 1933, replacing the terms ''anionoid'' and ''cation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons. Electrophiles mainly interact with nucleophiles through addition and substitution reactions. Frequently seen electrophiles in organic syntheses include cations such as H+ and NO+, polarized neutral molecules such as HCl, alkyl halides, acyl halides, and carbonyl compounds, polarizable neutral molecules such as Cl2 and Br2, oxidizing agents such as organic peracids, chemical species that do not satisfy the octet rule such as carbenes and radicals, and some Lewis acids such as BH3 and DIBAL. Organic chemistry Addition of halogens These occur between alkenes and electrophiles, often halogens as in halogen addition reactions. Comm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Effect
The alpha effect refers to the increased nucleophilicity of an atom due to the presence of an adjacent (alpha) atom with lone pair electrons. This first atom does not necessarily exhibit increased basicity compared with a similar atom without an adjacent electron-donating atom, resulting in a deviation from the classical Brønsted-type reactivity-basicity relationship. In other words, the alpha effect refers to nucleophiles presenting higher nucleophilicity than the predicted value obtained from the Brønsted basicity. The representative examples would be high nucleophilicities of hydroperoxide (HO2−) and hydrazine (N2H4). The effect is now well established with numerous examples and became an important concept in mechanistic chemistry and biochemistry. However, the origin of the effect is still controversial without a clear winner. Background Experiment The effect was first observed by Jencks and Carriuolo in 1960 in a series of chemical kinetics experiments involving ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
-phil-
The Greek root "-Phil-" originates from the Greek word meaning "love". For example, Philosophy (along with the Greek root "-soph-" meaning "wisdom") is the study of human customs and the significance of life. One of the most common uses of the root "-phil-" is with philias. A philia is the love or obsession with a particular thing or subject. The suffix -philia is used to specify the love or obsession with something more specific. It is somewhat antonymic to -phobia. Philias can be biological (e. g. Rhizophilia, preference for living on roots), or Chemical (e. g. Chromophilous, materials that stain easily), or can be a hobby/liking (e. g. Icthyophilia, love for fish). ''Philia'' () as a Greek word for love refers to brotherly love, including friendship and affection. This contrasts to the Greek terms Eros, or sexual/ romantic love, and agape, or detached, spiritual love. However, English usage differs in some cases from the eytmological use, and several of these words refe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic Substitution
In chemistry, a nucleophilic substitution is a class of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...s in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). The molecule that contains the electrophile and the leaving functional group is called the Substrate (chemistry), substrate. The most general form of the reaction may be given as the following: :\text\mathbf + \ce + \text\mathbf The electron pair (:) from the nucleophile (Nuc) wiktionary:attack#Verb, attacks the substrate () and bonds with it. Simultaneously, the leaving group (LG) departs with an electron pair. The principal product in this case is . The nucleophile may be electricall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Pair
In chemistry, an electron pair or Lewis pair consists of two electrons that occupy the same molecular orbital but have opposite spins. Gilbert N. Lewis introduced the concepts of both the electron pair and the covalent bond in a landmark paper he published in 1916. Because electrons are fermions, the Pauli exclusion principle forbids these particles from having the same quantum numbers. Therefore, for two electrons to occupy the same orbital, and thereby have the same orbital quantum number, they must have different spin quantum number. This also limits the number of electrons in the same orbital to two. The pairing of spins is often energetically favorable, and electron pairs therefore play a large role in chemistry. They can form a chemical bond between two atoms, or they can occur as a lone pair of valence electrons. They also fill the core levels of an atom. Because the spins are paired, the magnetic moment of the electrons cancel one another, and the pair's contri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basicity
In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century. In 1884, Svante Arrhenius proposed that a base is a substance which dissociates in aqueous solution to form Hydroxide ions OH−. These ions can react with hydrogen ions (H+ according to Arrhenius) from the dissociation of acids to form water in an acid–base reaction. A base was therefore a metal hydroxide such as NaOH or Ca(OH)2. Such aqueous hydroxide solutions were also described by certain characteristic properties. They are slippery to the touch, can taste bitter and change the color of pH indicators (e.g., turn red litmus paper blue). In water, by altering the autoionization equilibrium, bases yield solutions in which the hydrogen ion activity is lower than it is in pure water, i.e., the wat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudo First Order Reaction
In chemistry, the rate law or rate equation for a reaction is an equation that links the initial or forward reaction rate with the concentrations or pressures of the reactants and constant parameters (normally rate coefficients and partial reaction orders). For many reactions, the initial rate is given by a power law such as :v_0\; =\; k mathrmx mathrmy where and express the concentration of the species and usually in moles per liter ( molarity, ). The exponents and are the partial ''orders of reaction'' for and and the ''overall'' reaction order is the sum of the exponents. These are often positive integers, but they may also be zero, fractional, or negative. The constant is the reaction rate constant or ''rate coefficient'' of the reaction. Its value may depend on conditions such as temperature, ionic strength, surface area of an adsorbent, or light irradiation. If the reaction goes to completion, the rate equation for the reaction rate v\; =\; k cex cey applies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reaction Rate Constant
In chemical kinetics a reaction rate constant or reaction rate coefficient, ''k'', quantifies the rate and direction of a chemical reaction. For a reaction between reactants A and B to form product C the reaction rate is often found to have the form: r = k(T) mathrmm mathrm Here ''k''(''T'') is the reaction rate constant that depends on temperature, and and are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.) The exponents ''m'' and ''n'' are called partial orders of reaction and are ''not'' generally equal to the stoichiometric coefficients ''a'' and ''b''. Instead they depend on the reaction mechanism and can be determined experimentally. Elementary steps For an elementary step, there ''is'' a relationship between stoichiometry and rate law, as determined b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methyl Bromide
Bromomethane, commonly known as methyl bromide, is an organobromine compound with formula C H3 Br. This colorless, odorless, nonflammable gas is produced both industrially and biologically. It has a tetrahedral shape and it is a recognized ozone-depleting chemical. It was used extensively as a pesticide until being phased out by most countries in the early 2000s. Occurrence and manufacture Bromomethane originates from both natural and human sources. In the ocean, marine organisms are estimated to produce 56,000 tonnes annually. It is also produced in small quantities by certain terrestrial plants, such as members of the family Brassicaceae. It is manufactured for agricultural and industrial use by treating methanol with bromine in the presence of sulfur or hydrogen sulfide: :6 CH3OH + 3 Br2 + S → 6 CH3Br + 2 H2O + H2SO4 Uses In 1999, an estimated 71,500 tonnes of synthetic methyl bromide were used annually worldwide. 97% of this estimate was used for fumigation purposes, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often very soluble in water.Green, John, and Sadru Damji. "Chapter 3." ''Chemistry''. Camberwell, Vic.: IBID, 2001. Print. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating liquid flow in and out of cells. Less frequently, the word ''chloride'' may also form part of the "common" name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane (see IUPAC books) is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion. Electronic properties A chloride ion (diameter 167 pm) is much lar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetate
An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called an anion) typically found in aqueous solution and written with the chemical formula . The neutral molecules formed by the combination of the acetate ion and a ''positive'' ion (called a cation) are also commonly called "acetates" (hence, ''acetate of lead'', ''acetate of aluminum'', etc.). The simplest of these is hydrogen acetate (called acetic acid) with corresponding salts, esters, and the polyatomic anion , or . Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In nature, acetate is the most common building block for biosynthesis. Nomenclature and common formula When part of a salt, the formula of the acetate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Azide
In chemistry, azide is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant application of azides is as a propellant in air bags. Preparation Sodium azide is made industrially by the reaction of nitrous oxide, with sodium amide in liquid ammonia as solvent: : Many inorganic azides can be prepared directly or indirectly from sodium azide. For example, lead azide, used in detonators, may be prepared from the metathesis reaction between lead nitrate and sodium azide. An alternative route is direct reaction of the metal with silver azide dissolved in liquid ammonia. Some azides are produced by treating the carbonate salts with hydrazoic acid. Bonding Azide is isoelectronic with carbon dioxide , cyanate , nitrous oxide , nitronium ion and cyanogen fluoride NCF. Per valence bond theory, azide can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
