CarbeneIn organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" may also refer to the specific compound , also called methylene, the parent hydride from which all other carbene compounds are formally derived. Carbenes are classified as either singlets or triplets, depending upon their electronic structure.
Alkyl groupIn organic chemistry, an alkyl group is an alkane missing one hydrogen. The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cycloalkane by removal of a hydrogen atom from a ring and has the general formula . Typically an alkyl is a part of a larger molecule. In structural formulae, the symbol R is used to designate a generic (unspecified) alkyl group. The smallest alkyl group is methyl, with the formula .
Carbonium ionIn chemistry, a carbonium ion is any cation that has a pentacoordinated carbon atom. The name carbonium may also be used for the simplest member of the class, properly called methanium (), where the carbon atom is covalently bonded to five hydrogen atoms. The next simplest carbonium ions after methanium have two carbon atoms. Ethynium, or protonated acetylene , and ethenium are usually classified in other families. The ethanium ion has been studied as an extremely rarefied gas by infrared spectroscopy.
NucleophileIn 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.
AlkylationAlkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting alkylation. Alkyl groups can also be removed in a process known as dealkylation. Alkylating agents are often classified according to their nucleophilic or electrophilic character. In oil refining contexts, alkylation refers to a particular alkylation of isobutane with olefins.
Hypervalent moleculeIn chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pentachloride (), sulfur hexafluoride (), chlorine trifluoride (), the chlorite () ion, and the triiodide () ion are examples of hypervalent molecules. Hypervalent molecules were first formally defined by Jeremy I. Musher in 1969 as molecules having central atoms of group 15–18 in any valence other than the lowest (i.
Benzyl groupIn organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group. In IUPAC nomenclature, the prefix benzyl refers to a substituent, for example benzyl chloride or benzyl benzoate. Benzyl is not to be confused with phenyl with the formula . The term benzylic is used to describe the position of the first carbon bonded to a benzene or other aromatic ring. For example, is referred to as a "benzylic" carbocation.
Arenium ionAn arenium ion in organic chemistry is a cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution. For historic reasons this complex is also called a Wheland intermediate, after American chemist George Willard Wheland (1907–1976). They are also called sigma complexes. The smallest arenium ion is the benzenium ion (C6H7+), which is protonated benzene. Two hydrogen atoms bonded to one carbon lie in a plane perpendicular to the benzene ring.
Onium ionIn chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake for the class, is ammonium, , the protonated derivative of ammonia, . The name onium is also used for cations that would result from the substitution of hydrogen atoms in those ions by other groups, such as organic groups, or halogens; such as tetraphenylphosphonium, .
Rearrangement reactionIn organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another atom in the same molecule, hence these reactions are usually intramolecular. In the example below, the substituent R moves from carbon atom 1 to carbon atom 2: Intermolecular rearrangements also take place.
