In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon atoms. Allenes are classified as cumulated dienes. The parent compound of this class is propadiene, which is itself also called allene. A group of the structure R2C=C=CR− is called allenyl, while a substituent attached to an allene is referred to as an allenic substituent. In analogy to allylic and propargylic, a substituent attached to a saturated carbon α to an allene is referred to as an allenylic substituent. While allenes have two consecutive ('cumulated') double bonds, compounds with three or more cumulated double bonds are called cumulenes.
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.
In organic chemistry, an imide is a functional group consisting of two acyl groups bound to nitrogen. The compounds are structurally related to acid anhydrides, although imides are more resistant to hydrolysis. In terms of commercial applications, imides are best known as components of high-strength polymers, called polyimides. Inorganic imides are also known as solid state or gaseous compounds, and the imido group (=NH) can also act as a ligand.
In organic chemistry, the ene reaction is a chemical reaction between an alkene with an allylic hydrogen and a compound containing a multiple bond, in order to form a new σ-bond with migration of the ene double bond and 1,5 hydrogen shift. The product is a substituted alkene with the double bond shifted to the allylic position.
Cyclohexanone is the organic compound with the formula (CH2)5CO. The molecule consists of six-carbon cyclic molecule with a ketone functional group. This colorless oily liquid has a sweet odor reminiscent of benzaldehyde. Over time, samples of cyclohexanone assume a pale yellow color. Cyclohexanone is slightly soluble in water and miscible with common organic solvents. Millions of tonnes are produced annually, mainly as a precursor to nylon.
An alkyne trimerisation is a [2+2+2] cycloaddition reaction in which three alkyne units react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applicable to organic synthesis. Being a cycloaddition reaction, it has high atom economy. Many variations have been developed, including cyclisation of mixtures of alkynes and alkenes as well as alkynes and nitriles.
In chemistry, axial chirality is a special case of chirality in which a molecule contains two pairs of chemical groups in a non-planar arrangement about an axis of chirality so that the molecule is not superposable on its mirror image. The axis of chirality is usually determined by a chemical bond that is constrained against free rotation either by steric hindrance of the groups, as in substituted biaryl compounds such as BINAP, or by torsional stiffness of the bonds, as in the C=C double bonds in allenes such as glutinic acid. Axial chirality is most commonly observed in substituted biaryl compounds wherein the rotation about the aryl–aryl bond is restricted so it results in chiral atropisomers, as in various ortho-substituted biphenyls, and in binaphthyls such as BINAP.
The Pauson–Khand (PK) reaction is a chemical reaction, described as a [2+2+1] cycloaddition. In it, an alkyne, an alkene, and carbon monoxide combine into a α,β-cyclopentenone in the presence of a metal-carbonyl catalyst Ihsan Ullah Khand (1935–1980) discovered the reaction around 1970, while working as a postdoctoral associate with Peter Ludwig Pauson (1925–2013) at the University of Strathclyde in Glasgow. Pauson and Khand's initial findings were intermolecular in nature, but the reaction has poor selectivity. Some modern applications instead apply the reaction for intramolecular ends.
In organic chemistry, a dicarboxylic acid is an organic compound containing two carboxyl groups. The general molecular formula for dicarboxylic acids can be written as HO2C−R−CO2H, where R can be aliphatic or aromatic. In general, dicarboxylic acids show similar chemical behavior and reactivity to monocarboxylic acids.
A polyyne is any organic compound with alternating single and triple bonds; that is, a series of consecutive alkynes, (−C≡C−)n with n greater than 1. These compounds are also called polyacetylenes, especially in the natural products and chemical ecology literature, even though this nomenclature more properly refers to acetylene polymers composed of alternating single and double bonds (−CR=CR′−)n with n greater than 1. They are also sometimes referred to as oligoynes, or carbinoids after "carbyne" (−C≡C−)∞, the hypothetical allotrope of carbon that would be the ultimate member of the series. The synthesis of this substance has been claimed several times since the 1960s, but those reports have been disputed. Indeed, the substances identified as short chains of "carbyne" in many early organic synthesis attempts would be called polyynes today.
Isocyanic acid is a chemical compound with the structural formula HNCO, which is often written as H−N=C=O. It is a colourless, volatile and poisonous substance, with a boiling point of 23.5 °C. It is the predominant tautomer and an isomer of cyanic acid (aka. cyanol).
In organic chemistry, a cycloalkyne is the cyclic analog of an alkyne. A cycloalkyne consists of a closed ring of carbon atoms containing one or more triple bonds. Cycloalkynes have a general formula CnH2n−4. Because of the linear nature of the C−C≡C−C alkyne unit, cycloalkynes can be highly strained and can only exist when the number of carbon atoms in the ring is great enough to provide the flexibility necessary to accommodate this geometry. Large alkyne-containing carbocycles may be virtually unstrained, while the smallest constituents of this class of molecules may experience so much strain that they have yet to be observed experimentally. Cyclooctyne is the smallest cycloalkyne capable of being isolated and stored as a stable compound. Despite this, smaller cycloalkynes can be produced and trapped through reactions with other organic molecules or through complexation to transition metals.
Ciguatoxins are a class of toxic polycyclic polyethers found in fish that cause ciguatera.
The Meyer–Schuster rearrangement is the chemical reaction described as an acid-catalyzed rearrangement of secondary and tertiary propargyl alcohols to α,β-unsaturated ketones if the alkyne group is internal and α,β-unsaturated aldehydes if the alkyne group is terminal. Reviews have been published by Swaminathan and Narayan, Vartanyan and Banbanyan, and Engel and Dudley, the last of which describes ways to promote the Meyer–Schuster rearrangement over other reactions available to propargyl alcohols.
The vinyl cation is a carbocation with the positive charge on an alkene carbon. Its empirical formula is C
2H+
3. More generally, a vinylic cation is any disubstituted carbon, where the carbon bearing the positive charge is part of a double bond and is sp hybridized. In the chemical literature, substituted vinylic cations are often referred to as vinyl cations, and understood to refer to the broad class rather than the C
2H+
3 variant alone. The vinyl cation is one of the main types of reactive intermediates involving a non-tetrahedrally coordinated carbon atom, and is necessary to explain a wide variety of observed reactivity trends. Vinyl cations are observed as reactive intermediates in solvolysis reactions, as well during electrophilic addition to alkynes, for example, through protonation of an alkyne by a strong acid. As expected from its sp hybridization, the vinyl cation prefers a linear geometry. Compounds related to the vinyl cation include allylic carbocations and benzylic carbocations, as well as aryl carbocations.
In chemistry, methanetetracarboxylate is a tetravalent anion with formula C5O4−8 or C(−CO−2)4. It has four carboxylate groups attached to a central carbon atom; so it has the same carbon backbone as neopentane. It is an oxocarbon anion, that is, consists only of carbon and oxygen.
2-Decendioic acid is a chemical compound classified as a fatty acid and a dicarboxylic acid.
The Crabbé reaction is an organic reaction that converts a terminal alkyne and aldehyde into an allene in the presence of a soft Lewis acid catalyst and secondary amine. Given continued developments in scope and generality, it is a convenient and increasingly important method for the preparation of allenes, a class of compounds often viewed as exotic and synthetically challenging to access.
Lewisite 2(L-2) is an organoarsenic chemical weapon with the formula AsCl(CH=CHCl)2. It is similar to lewisite 1 and lewisite 3 and was first synthesized in 1904 by Julius Arthur Nieuwland. It is usually found as a mixture of 2-chlorovinylarsonous dichloride (lewisite 1) as well as bis(2-chloroethenyl) arsinous chloride (lewisite 2) and tris(2-chlorovinyl)arsine (lewisite 3). Pure lewisite 1 is an oily, colorless liquid, however, the impure mixture can appear amber to black with an odor distinct to geraniums.
Lewisite 3(L-3) is an organoarsenic chemical weapon like lewisite 1 and lewisite 2 first synthesized in 1904 by Julius Arthur Nieuwland. It is usually found as a mixture of 2-chlorovinylarsonous dichloride as well as bis(2-chloroethenyl) arsinous chloride and tris(2-chlorovinyl)arsine. Pure lewisite 1 is an oily, colorless liquid, however, the impure mixture can appear amber to black with an odor distinct to geraniums.
