Alkyl group

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Isopropyl group
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

methyl, with the formula −CH3.[3]

Related concepts

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

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

interstellar space
as well.

Nomenclature

Alkyl groups form

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 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 their

3-methylpentane
:

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.)

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 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

Etymology

The first named alkyl radical was ethyl, named so by

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

Look up alkyl group in Wiktionary, the free dictionary.

References

  1. doi:10.1351/goldbook.A00228
  2. doi:10.1351/goldbook.C01498
  3. ^ Virtual Textbook of Organic Chemistry Naming Organic Compounds Archived 2016-05-21 at the Portuguese Web Archive
  4. S2CID 5159000
    .
  5. ISSN 0001-4842
    .
  6. PMID 32786419
    .
  7. ISBN 978-3-642-27415-2
    . Ethyl radicals (named by Liebig in 1833 from the Greek and German word "aether" plus Greek "hyle"
  8. 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. 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. 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. doi:10.1002/jlac.18822120107
    .
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