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Lewis Acid Catalysis
In organic chemistry, Lewis acid catalysis is the use of metal-based Lewis acids as catalysts for organic reactions. The acids act as an Electron acceptor, electron pair acceptor to increase the Reactivity (chemistry), reactivity of a Substrate (chemistry), substrate. Common Lewis acid catalysts are based on Main-group element, main group metals such as aluminum, boron, silicon, and tin, as well as many early (titanium, zirconium) and late (iron, copper, zinc) d-block metals. The metal atom forms an adduct with a lone-pair bearing electronegative atom in the substrate, such as oxygen (both sp2 or sp3), nitrogen, sulfur, and halogens. The Coordination complex, complexation has partial charge-transfer character and makes the Electron donor, lone-pair donor effectively more electronegative, activating the substrate toward nucleophilic attack, heterolytic bond cleavage, or cycloaddition with 1,3-dienes and 1,3-dipoles. Many classical reactions involving Carbon–carbon bond, carbon– ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First Lewis Acid-catalyzed Diels-Alder Reaction
First most commonly refers to: * First, the ordinal form of the number 1 First or 1st may also refer to: Acronyms * Faint Images of the Radio Sky at Twenty-Centimeters, an astronomical survey carried out by the Very Large Array * Far Infrared and Sub-millimetre Telescope, of the Herschel Space Observatory * For Inspiration and Recognition of Science and Technology, an international youth organization * Forum of Incident Response and Security Teams, a global forum Arts and entertainment Albums * ''1st'' (album), by Streets, 1983 * ''1ST'' (SixTones album), 2021 * ''First'' (David Gates album), 1973 * ''First'', by Denise Ho, 2001 * ''First'' (O'Bryan album), 2007 * ''First'' (Raymond Lam album), 2011 Extended plays * ''1st'', by The Rasmus, 1995 * ''First'' (Baroness EP), 2004 * ''First'' (Ferlyn G EP), 2015 Songs * "First" (Lindsay Lohan song), 2005 * "First" (Cold War Kids song), 2014 * "First", by Lauren Daigle from the album '' How Can It Be'', 2015 * "First", by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronegative
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons. Electronegativity serves as a simple way to quantitatively estimate the bond energy, and the sign and magnitude of a bond's chemical polarity, which characterizes a bond along the continuous scale from covalent to ionic bonding. The loosely defined term electropositivity is the opposite of electronegativity: it characterizes an element's tendency to donate valence electrons. On the most basic level, electronegativity is determined by factors like the nuclear charge (the more protons an atom has, the more "pull" it will have on electrons) and the number and locatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pericyclic
In organic chemistry, a pericyclic reaction is the type of organic reaction wherein the transition state of the molecule has a cyclic geometry, the reaction progresses in a concerted fashion, and the bond orbitals involved in the reaction overlap in a continuous cycle at the transition state. Pericyclic reactions stand in contrast to ''linear reactions'', encompassing most organic transformations and proceeding through an acyclic transition state, on the one hand and '' coarctate reactions'', which proceed through a doubly cyclic, concerted transition state on the other hand. Pericyclic reactions are usually rearrangement or addition reactions. The major classes of pericyclic reactions are given in the table below (the three most important classes are shown in bold). Ene reactions and cheletropic reactions are often classed as group transfer reactions and cycloadditions/cycloeliminations, respectively, while dyotropic reactions and group transfer reactions (if ene reactions ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aldol Reaction
The aldol reaction (aldol addition) is a Chemical reaction, reaction in organic chemistry that combines two Carbonyl group, carbonyl compounds (e.g. aldehydes or ketones) to form a new β-hydroxy carbonyl compound. Its simplest form might involve the nucleophilic addition of an Enolate, enolized ketone to another: These products are known as ''aldols'', from the ''ald''ehyde + alcoh''ol'', a structural motif seen in many of the products. The use of aldehyde in the name comes from its history: aldehydes are more reactive than ketones, so that the reaction was discovered first with them. The aldol reaction is paradigmatic in organic chemistry and one of the most common means of forming carbon–carbon bonds in organic chemistry. It lends its name to the family of aldol reactions and similar techniques analyze a whole family of carbonyl α-substitution reactions, as well as the Claisen condensation, diketone condensations. Scope Aldol structural units are found in many importa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon–carbon Bond
A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed between one hybridized orbital from each of the carbon atoms. In ethane, the orbitals are sp3- hybridized orbitals, but single bonds formed between carbon atoms with other hybridizations do occur (e.g. sp2 to sp2). In fact, the carbon atoms in the single bond need not be of the same hybridization. Carbon atoms can also form double bonds in compounds called alkenes or triple bonds in compounds called alkynes. A double bond is formed with an sp2-hybridized orbital and a p-orbital that is not involved in the hybridization. A triple bond is formed with an sp-hybridized orbital and two p-orbitals from each atom. The use of the p-orbitals forms a pi bond. Chains and branching Carbon is one of the few elements that can form long chains of its own atoms, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more Unsaturated hydrocarbon, unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the Multiplicity (chemistry)#Molecules, bond multiplicity". The resulting reaction is a cyclization reaction. Many but not all cycloadditions are Concerted reaction, concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic. As a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile. Cycloadditions can be described using two systems of notation. An older but still common notation is based on the size of linear arrangements of atoms in the reactants. It uses parentheses: where the variables are the numbers of linear atoms in each reactant. The product is a cycle of size . In this system, the standard Diels-Alder reaction is a (4 + 2)-cyc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterolytic Bond Cleavage
In chemistry, heterolysis or heterolytic fission () is the process of cleaving/breaking a covalent bond where one previously bonded Chemical species, species takes both original bonding electrons from the other species. During heterolytic bond cleavage of a neutral molecule, a cation and an anion will be generated. Most commonly the more Electronegativity, electronegative atom keeps the pair of electrons becoming anionic while the more electropositive atom becomes cationic. : Heterolytic fission almost always happens to single bonds; the process usually produces two fragment species. The energy required to break the bond is called the heterolytic bond dissociation energy, which is similar (but not equivalent) to homolytic bond dissociation energy commonly used to represent the Bond energy, energy value of a bond. One example of the differences in the energies is the energy required to break a bond : History The discovery and categorization of heterolytic bond fission was c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic Attack
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. The difference between the two is, that basicity is a thermodynamic property (i.e. relates to an equilibrium state), but nucleophilicity is a kinetic property ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Donor
In chemistry, an electron donor is a chemical entity that transfers electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. An obsolete definition equated an electron donor and a Lewis base. In contrast to traditional reducing agents, electron transfer from a donor to an electron acceptor may be only fractional. The electron is not completely transferred, which results in an Delocalized electron, electron resonance between the donor and acceptor. This leads to the formation of charge transfer complexes, in which the components largely retain their chemical identities. The electron donating power of a donor molecule is measured by its ionization potential, which is the energy required to remove an electron from the highest occupied molecular orbital (HOMO and LUMO, HOMO). The overall energy balance (ΔE), i.e., energy gained or lost, in an electron donor-acceptor transfer is determined by the difference bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coordination Complex
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many metal-containing chemical compound, compounds, especially those that include transition metals (elements like titanium that belong to the periodic table's d-block), are coordination complexes. Nomenclature and terminology Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A Ligand#Polydentate and polyhapto ligand motifs and nomenclature, polydentate (multiple bonded) ligand is a molecule or ion that bonds to the central atom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halogens
The halogens () are a group (periodic table), group in the periodic table consisting of six chemically related chemical element, elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would exclude tennessine as its chemistry is unknown and is theoretically expected to be more like that of gallium. In the modern IUPAC nomenclature, this group is known as group 17. The word "halogen" means "salt former" or "salt maker". When halogens react with metals, they produce a wide range of Salt (chemistry), salts, including calcium fluoride, sodium chloride (common table salt), silver bromide and potassium iodide. The group of halogens is the only Group (periodic table), periodic table group that contains elements in three of the main State of matter, states of matter at standard temperature and pressure, though not far above room temperature the same becomes true of groups alkali metals, 1 and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
