Alkyl group

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Isopropyl group Isopropyl group.svg
Isopropyl group
Methyl group Methyl2.svg
Methyl group

In organic chemistry, an alkyl group is an alkane missing one hydrogen. [1] The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of −CnH2n+1. A cycloalkyl group is derived from a cycloalkane by removal of a hydrogen atom from a ring and has the general formula −CnH2n−1. [2] 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 −CH3. [3]

Contents

Alkylation is the addition of alkyl groups to molecules, often by alkylating agents such as alkyl halides.

Alkylating antineoplastic agents are a class of compounds that are used to treat cancer. In such case, the term alkyl is used loosely. For example, nitrogen mustards are well-known alkylating agents, but they are not simple hydrocarbons.

In chemistry, alkyl is a group, a substituent, that is attached to other molecular fragments. For example, alkyl lithium reagents have the empirical formula Li(alkyl), where alkyl = methyl, ethyl, etc. A dialkyl ether is an ether with two alkyl groups, e.g., diethyl ether O(CH2CH3)2.

In medicinal chemistry

In medicinal chemistry, the incorporation of alkyl chains into some chemical compounds increases their lipophilicity. This strategy has been used to increase the antimicrobial activity of flavanones and chalcones. [4]

Alkyl cations, anions, and radicals

Usually, alkyl groups are attached to other atoms or groups of atoms. Free alkyls occur as neutral radicals, as anions, or as cations. The cations are called carbocations. The anions are called carbanions. The neutral alkyl free radicals have no special name. Such species are usually encountered only as transient intermediates. However, persistent alkyl radicals with half-lives "from seconds to years" have been prepared. [5] Typically alkyl cations are generated using superacids and alkyl anions are observed in the presence of strong bases. Alkyl radicals can be generated by a photochemical reaction or by homolytic cleavage. [6] Alkyls are commonly observed in mass spectrometry of organic compounds. Simple alkyls (especially methyl) are observed in the interstellar space as well.

Nomenclature

Alkyl groups form homologous series. The simplest series have the general formula −CnH2n+1. Alkyls include methyl , (−CH3), ethyl (−C2H5), propyl (−C3H7), butyl (−C4H9), pentyl (−C5H11), and so on. Alkyl groups that contain one ring have the formula −CnH2n−1, e.g. cyclopropyl and cyclohexyl. The formula of alkyl radicals are the same as alkyl groups, except the free valence "−" is replaced by the dot "•" and adding "radical" to the name of the alkyl group (e.g. methyl radical •CH3).

The naming convention is taken from IUPAC nomenclature:

Number of carbon atoms1234567891011121314
Prefixmeth-eth-prop-but-pent-hex-hept-oct-non-dec-undec-dodec-tridec-tetradec-
Group name Methyl Ethyl Propyl Butyl Pentyl HexylHeptylOctylNonylDecylUndecylDodecylTridecylTetradecyl


The prefixes taken from IUPAC nomenclature are used to name branched chained structures by their substituent groups, for example 3-methylpentane:

3-MethylPentaneHighlighted.svg

The structure of 3-methylpentane is viewed as consisting of two parts. First, five atoms comprise the longest straight chain of carbon centers. The parent five-carbon compound is named pentane (highlighted blue). The methyl "substituent" or "group" is highlighted red. According to the usual rules of nomenclature, alkyl groups are included in the name of the molecule before the root, as in methylpentane. This name is, however, ambiguous, as the methyl branch could be on various carbon atoms. Thus, the name is 3-methylpentane to avoid ambiguity: The 3- is because the methyl is attached to the third of the five carbon atoms.

If there is more than one of the same alkyl group attached to a chain, then the prefixes are used on the alkyl groups to indicate multiples (i.e., di, tri, tetra, etc.)

2,3,3triMethylPentane.svg

This compound is known as 2,3,3-trimethylpentane. Here three identical alkyl groups attached to carbon atoms 2, 3, and 3. The numbers are included in the name to avoid ambiguity about the position of the groups, and "tri" indicates that there are three identical methyl groups. If one of the methyl groups attached to the third carbon atom were instead an ethyl group, then the name would be 3-ethyl-2,3-dimethylpentane. When there are different alkyl groups, they are listed in alphabetical order.

In addition, each position on an alkyl chain can be described according to how many other carbon atoms are attached to it. The terms primary, secondary, tertiary, and quaternary refer to a carbon attached to one, two, three, or four other carbons respectively.

Cn Trivial name Symbol Condensed formula IUPAC statusPreferred IUPAC name Skeletal formula
С1 methyl Ме−CH3methyl
С2 ethyl Et−CH2−CH3ethyl
С3 propyl, n-propylPr, nPr, n-Pr−CH2−CH2−CH3propyl
isopropyliPr, i-Pr,iPr−CH(−CH3)22-propyl
С4n-butylBu, n-Bu, nBu−CH2−CH2−CH2−CH3butyl N-Butyl-Skeletal-SVG.svg
isobutyliBu, i-Bu, iBu−CH2−CH(−CH3)22-methylpropyl Isobutyl-Skeletal-SVG.svg
sec-butylsBu, s-Bu, sBu−CH(−CH3)−CH2−CH32-butyl Sec-Butyl-Skeletal-SVG.svg
tert-butyltBu, t-Bu, tBu−C(−CH3)3tert-butyl Tert-Butyl-Skeletal-SVG.svg
С5n-pentyl, amylPe, Am, nPe, n-Pe, nPe, nAm−CH2−CH2−CH2−CH2−CH3pentyl
tert-pentyltPe, t-Pe, tPe−C(−CH3)2−CH2−CH3No longer recommended2-methylbutan-2-yl (aka 1,1-dimethylpropyl)
neopentyl−CH2−C(−CH3)3No longer recommended2,2-dimethylpropyl
isopentyl, isoamyl−CH2−CH2−CH(−CH3)2No longer recommended3-methylbutyl
sec-pentylsPe, s-Pe, sPe−CH(−CH3)−CH2−CH2−CH3pentan-2-yl(or (1-Methylbutyl))
3-pentyl−CH(−CH2−CH3)2pentan-3-yl (also known as (1-Ethylpropyl))
sec-isopentyl, sec-isoamyl, siamylSia−CH(−CH3)−CH(−CH3)23-methylbutan-2-yl (or (1,2-Dimethylpropyl))
active pentyl−CH2−CH(−CH3)−CH2−CH32-methylbutyl

Etymology

The first named alkyl radical was ethyl, named so by Liebig in 1833 from the German word "Äther" (which in turn had been derived from the Greek word "aither" meaning "air", for the substance now known as diethyl ether) and the Greek word ύλη (hyle), meaning "matter". [7] This was followed by methyl (Dumas and Peligot in 1834, meaning "spirit of wood" [8] ) and amyl (Auguste Cahours in 1840 [9] ). The word alkyl was introduced by Johannes Wislicenus in or before 1882, based on the German word "Alkoholradikale" and then-common suffix -yl. [10] [11]

See also

Related Research Articles

<span class="mw-page-title-main">Alkane</span> Type of saturated hydrocarbon compound

In organic chemistry, an alkane, or paraffin, is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single. Alkanes have the general chemical formula CnH2n+2. The alkanes range in complexity from the simplest case of methane, where n = 1, to arbitrarily large and complex molecules, like pentacontane or 6-ethyl-2-methyl-5-(1-methylethyl) octane, an isomer of tetradecane.

<span class="mw-page-title-main">Alkene</span> Hydrocarbon compound containing one or more C=C bonds

In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.

<span class="mw-page-title-main">Ether</span> Organic compounds made of alkyl/aryl groups bound to oxygen (R–O–R)

In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom bonded to two organyl groups. They have the general formula R−O−R′, where R and R′ represent the organyl groups. Ethers can again be classified into two varieties: if the organyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anaesthetic diethyl ether, commonly referred to simply as "ether". Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.

<span class="mw-page-title-main">Ester</span> Compound derived from an acid

In chemistry, an ester is a functional group derived from an acid in which the hydrogen atom (H) of at least one acidic hydroxyl group of that acid is replaced by an organyl group. Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well, but not according to the IUPAC.

<span class="mw-page-title-main">Ketone</span> Organic compounds of the form >C=O

In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.

In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula CH3. In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many organic compounds. It is a very stable group in most molecules. While the methyl group is usually part of a larger molecule, bonded to the rest of the molecule by a single covalent bond, it can be found on its own in any of three forms: methanide anion, methylium cation or methyl radical. The anion has eight valence electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed.

In chemistry, a structural isomer of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term metamer was formerly used for the same concept.

<span class="mw-page-title-main">Haloalkane</span> Group of chemical compounds derived from alkanes containing one or more halogens

The haloalkanes are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially. They are used as flame retardants, fire extinguishants, refrigerants, propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes that contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halomethane. Haloalkane or alkyl halides are the compounds which have the general formula "RX" where R is an alkyl or substituted alkyl group and X is a halogen.

<span class="mw-page-title-main">Ethyl group</span> Chemical group (–CH₂–CH₃)

In organic chemistry, an ethyl group is an alkyl substituent with the formula −CH2CH3, derived from ethane. Ethyl is used in the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry for a saturated two-carbon moiety in a molecule, while the prefix "eth-" is used to indicate the presence of two carbon atoms in the molecule.

<span class="mw-page-title-main">Alkylation</span> Transfer of an alkyl group from one molecule to another

Alkylation 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. 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. For upgrading of petroleum, alkylation produces a premium blending stock for gasoline. In medicine, alkylation of DNA is used in chemotherapy to damage the DNA of cancer cells. Alkylation is accomplished with the class of drugs called alkylating antineoplastic agents.

In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in the Nomenclature of Organic Chemistry. Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. There is also an IUPAC nomenclature of inorganic chemistry.

<span class="mw-page-title-main">Skeletal formula</span> Representation method in chemistry

The skeletal formula, line-angle formula, bond-line formula or shorthand formula of an organic compound is a type of molecular structural formula that serves as a shorthand representation of a molecule's bonding and some details of its molecular geometry. A skeletal formula shows the skeletal structure or skeleton of a molecule, which is composed of the skeletal atoms that make up the molecule. It is represented in two dimensions, as on a piece of paper. It employs certain conventions to represent carbon and hydrogen atoms, which are the most common in organic chemistry.

In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula −C4H9, derived from either of the two isomers (n-butane and isobutane) of butane.

In organic chemistry, a substituent is one or a group of atoms that replaces atoms, thereby becoming a moiety in the resultant (new) molecule.

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<span class="mw-page-title-main">Xanthate</span> Salt that is a metal-thioate/O-esters of dithiocarbonate

A xanthate is a salt or ester of a xanthic acid. The formula of the salt of xanthic acid is [R−O−CS2]−M+. Xanthate also refers to the anion [R−O−CS2]−. The formula of a xanthic acid is R−O−C(=S)−S−H, such as ethyl xanthic acid, while the formula of an ester of a xanthic acid is R−O−C(=S)−S−R', where R and R' are organyl groups. The salts of xanthates are also called O-organyl dithioates. The esters of xanthic acid are also called O,S-diorganyl esters of dithiocarbonic acid. The name xanthate is derived from Ancient Greek ξανθός (xanthos) meaning 'yellowish' or 'golden', and indeed most xanthate salts are yellow. They were discovered and named in 1823 by Danish chemist William Christopher Zeise. These organosulfur compounds are important in two areas: the production of cellophane and related polymers from cellulose and for extraction of certain sulphide bearing ores. They are also versatile intermediates in organic synthesis.

<span class="mw-page-title-main">Pentyl group</span> Chemical compound

Pentyl is a five-carbon alkyl group or substituent with chemical formula -C5H11. It is the substituent form of the alkane pentane.

The root alk- is used in organic chemistry to form classification names for classes of organic compounds which contain a carbon skeleton but no aromatic rings. It was extracted from the word alcohol by removing the -ol suffix. See e.g. alkyl, alkane.

In chemistry, a reaction intermediate, or intermediate, is a molecular entity arising within the sequence of a stepwise chemical reaction. It is formed as the reaction product of an elementary step, from the reactants and/or preceding intermediates, but is consumed in a later step. It does not appear in the chemical equation for the overall reaction.

<span class="mw-page-title-main">Thioanisole</span> Chemical compound

Thioanisole is an organic compound with the formula CH3SC6H5. It is a colorless liquid that is soluble in organic solvents. It is the simplest alkyl–aryl thioether. The name indicates that this compound is the sulfur analogue—the thioether rather than the oxygen-centered ether—of anisole.

References

  1. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " alkyl groups ". doi : 10.1351/goldbook.A00228
  2. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " cycloalkyl groups ". doi : 10.1351/goldbook.C01498
  3. ↑ Virtual Textbook of Organic Chemistry Naming Organic Compounds Archived 2016-05-21 at the Portuguese Web Archive
  4. ↑ Mallavadhani UV, Sahoo L, Kumar KP, Murty US (2013). "Synthesis and antimicrobial screening of some novel chalcones and flavanones substituted with higher alkyl chains". Medicinal Chemistry Research. 23 (6): 2900–2908. doi:10.1007/s00044-013-0876-x. S2CID   5159000.
  5. ↑ Griller, David; Ingold, Keith U. (1976-01-01). "Persistent carbon-centered radicals". Accounts of Chemical Research. 9 (1): 13–19. doi:10.1021/ar50097a003. ISSN   0001-4842.
  6. ↑ Crespi, Stefano; Fagnoni, Maurizio (2020-09-09). "Generation of Alkyl Radicals: From the Tyranny of Tin to the Photon Democracy". Chemical Reviews. 120 (17): 9790–9833. doi:10.1021/acs.chemrev.0c00278. ISSN   0009-2665. PMC   8009483 . PMID   32786419.
  7. ↑ Rocke, Alan (2012). From the Molecular World: A Nineteenth-Century Science Fantasy. Springer. p. 62. ISBN   978-3-642-27415-2. Ethyl radicals (named by Liebig in 1833 from the Greek and German word "aether" plus Greek "hyle"
  8. ↑ Rocke, Alan (2012). From the Molecular World: A Nineteenth-Century Science Fantasy. Springer. p. 62. ISBN   978-3-642-27415-2. The methyl radical ... named from Greek roots, by Dumas and Peligot in 1834: methyl = methy + hyle ("spirit" + "wood")
  9. ↑ Rocke, Alan (2012). From the Molecular World: A Nineteenth-Century Science Fantasy. Springer. p. 62. ISBN   978-3-642-27415-2. Amyl radicals ("amilène" was coined by Auguste Cahours in 1840, to designate a substance from potato starch after fermentation and distillation
  10. ↑ Rocke, Alan (2012). From the Molecular World: A Nineteenth-Century Science Fantasy. Springer. p. 62. ISBN   978-3-642-27415-2. "Alkyl" was coined without fanfare by Johannes Wislicenus, professor at Würzburg; an early use (perhaps not the first) is in his 1882 article [22, 244]. The word was derived from the first three letters of "Alkoholradicale" combined with the suffix -yl; it was (and is) a generic term for any of those radicals who bear the "first names" methyl, ethyl, propyl, butyl, amyl, etc.
  11. ↑ Wisclicenus, Johannes (1882). "Ueber die Schätzung von Haftenenergien der Halogene und des Natriums an organischen Resten". Ann. Chem. 212: 239–250. doi:10.1002/jlac.18822120107.
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