Inorganic chemistry, analkyl group is analkane missing onehydrogen.[1]The termalkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of−CnH2n+1. Acycloalkyl group is derived from acycloalkane by removal of a hydrogen atom from aring and has the general formula−CnH2n−1.[2]Typically an alkyl is a part of a larger molecule. Instructural formulae, the symbol R is used to designate a generic (unspecified) alkyl group. The smallest alkyl group ismethyl, with the formula−CH3.[3]
Alkylation is the addition of alkyl groups to molecules, often by alkylating agents such asalkyl 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. Adialkyl ether is anether with two alkyl groups, e.g., diethyl etherO(CH2CH3)2.
Inmedicinal chemistry, the incorporation of alkyl chains into somechemical compounds increases theirlipophilicity. This strategy has been used to increase the antimicrobial activity offlavanones andchalcones.[4]
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 calledcarbocations. The anions are calledcarbanions. The neutral alkylfree radicals have no special name. Such species are usually encountered only as transient intermediates. However, persistent alkyl radicals withhalf-lives "from seconds to years" have been prepared.[5] Typically alkyl cations are generated usingsuperacids and alkyl anions are observed in the presence of strong bases. Alkyl radicals can be generated by aphotochemical reaction or byhomolytic cleavage.[6] Alkyls are commonly observed inmass spectrometry oforganic compounds. Simple alkyls (especiallymethyl) are observed in theinterstellar space as well.[citation needed]
Alkyl groups formhomologous series. The simplest series have the general formula−CnH2n+1. Alkyls includemethyl, (−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 fromIUPAC nomenclature:
| Number of carbon atoms | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Prefix | meth- | eth- | prop- | but- | pent- | hex- | hept- | oct- | non- | dec- | undec- | dodec- | tridec- | tetradec- |
| Group name | Methyl | Ethyl | Propyl | Butyl | Pentyl | Hexyl | Heptyl | Octyl | Nonyl | Decyl | Undecyl | Dodecyl | Tridecyl | Tetradecyl |
The prefixes taken from IUPAC nomenclature are used to name branched chained structures by theirsubstituent groups, for example3-methylpentane:
The structure of3-methylpentane is viewed as consisting of two parts. First, five atoms comprise the longest straight chain ofcarbon centers. The parent five-carbon compound is namedpentane (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 inmethylpentane. 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.)
This compound is known as2,3,3-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 termsprimary,secondary,tertiary, andquaternary refer to a carbon attached to one, two, three, or four other carbons respectively.
| Cn | Trivial name | Symbol | Condensed formula | IUPAC status | Preferred IUPAC name | Skeletal formula |
|---|---|---|---|---|---|---|
| С1 | methyl | Ме | −CH3 | methyl | ||
| С2 | ethyl | Et | −CH2−CH3 | ethyl | ||
| С3 | propyl,n-propyl | Pr,nPr,n-Pr | −CH2−CH2−CH3 | propyl | ||
| isopropyl | iPr,i-Pr,iPr | −CH(−CH3)2 | 2-propyl | |||
| С4 | n-butyl | Bu,n-Bu,nBu | −CH2−CH2−CH2−CH3 | butyl |  | |
| isobutyl | iBu,i-Bu,iBu | −CH2−CH(−CH3)2 | 2-methylpropyl |  | ||
| sec-butyl | sBu,s-Bu,sBu | −CH(−CH3)−CH2−CH3 | 2-butyl |  | ||
| tert-butyl | tBu,t-Bu,tBu | −C(−CH3)3 | tert-butyl |  | ||
| С5 | n-pentyl, amyl | Pe, Am,nPe,n-Pe,nPe,nAm | −CH2−CH2−CH2−CH2−CH3 | pentyl | ||
| tert-pentyl | tPe,t-Pe,tPe | −C(−CH3)2−CH2−CH3 | No longer recommended | 2-methylbutan-2-yl (aka 1,1-dimethylpropyl) | ||
| neopentyl | −CH2−C(−CH3)3 | No longer recommended | 2,2-dimethylpropyl | |||
| isopentyl, isoamyl | −CH2−CH2−CH(−CH3)2 | No longer recommended | 3-methylbutyl | |||
| sec-pentyl | sPe,s-Pe,sPe | −CH(−CH3)−CH2−CH2−CH3 | pentan-2-yl(or (1-Methylbutyl)) | |||
| 3-pentyl | −CH(−CH2−CH3)2 | pentan-3-yl (also known as (1-Ethylpropyl)) | ||||
| sec-isopentyl,sec-isoamyl, siamyl | Sia | −CH(−CH3)−CH(−CH3)2 | 3-methylbutan-2-yl (or (1,2-Dimethylpropyl)) | |||
| active pentyl | −CH2−CH(−CH3)−CH2−CH3 | 2-methylbutyl |
The first named alkyl radical was ethyl, named so byLiebig 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 asdiethyl ether) and the Greek word ύλη (hyle), meaning "matter".[7] This was followed by methyl (Dumas andPeligot in 1834, meaning "spirit of wood"[8]) and amyl (Auguste Cahours in 1840[9]). The word alkyl was introduced byJohannes Wislicenus in or before 1882, based on the German word "Alkoholradikale" and then-common suffix -yl.[10][11]
Ethyl radicals (named by Liebig in 1833 from the Greek and German word "aether" plus Greek "hyle"
The methyl radical ... named from Greek roots, by Dumas and Peligot in 1834: methyl = methy + hyle ("spirit" + "wood")
Amyl radicals ("amilène" was coined by Auguste Cahours in 1840, to designate a substance from potato starch after fermentation and distillation
"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.
