Methyl group

See also: Methylation
Methyl group
Preferred IUPAC name
Methyl group
Systematic name
Methyl
Other names
Methyl radical
Identifiers
CAS number 2229-07-4, 2122-44-3 (2H3)
PubChem 3034819 YesY, 137438 (2H3) YesY
ChemSpider 2299212 YesY, 121105 (2H3) YesY
MeSH Methyl+radical
ChEBI 293​09
Beilstein Reference 1696831
Gmelin Reference 57
Properties
Molecular formula CH3
Molar mass 15.03 g mol−1
Exact mass 15.023475 u
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

In chemistry, a methyl group is a hydrophobic alkyl functional group named after methylene (RCH2R or CH3OH). It has the formula -CH3 and is often abbreviated -Me. Such hydrocarbon groups occur in many organic compounds.

Methyl groups can be incorporated into organic compounds by an SN2 reaction on iodomethane, or by the reaction of methyl lithium or MeMgCl with a carbon atom that is substituted with a leaving group.

Contents

Reactivity

The methyl group can be found in 3 forms: anion, cation and radical. The anion has 8 electrons, the radical 7 and the cation 6. They are all reactive due to there being no stabilising effects such as induction or delocalization.

The introduction of methyl groups as substituents into a compound usually increases its lipophilicity and reduces its solubility in water. It should ease its absorption into biological membranes and make its release into aqueous surroundings more difficult. Incorporating a methyl group into a molecule can have any of three effects, each increasing its reactivity (the rate of its metabolism):

  1. by oxidizing the methyl group,
  2. by demethylation (the transfer of the methyl group to another compound), or
  3. by reduction, reducing the analogue.

The reactivity of a methyl group depends on what it is attached to. When occurring in an alkane, it is quite unreactive and resists all but the strongest of acids, bases, oxidizing agents, and reducing agents. But, in toluene, C6H5CH3, the methyl group is considerably more reactive, due to the electron-donating propensity of the ring. Electrophilic reagents are then able to attack the methyl group. For example, oxidation with permanganate converts the methyl group to carboxyl (-COOH), to produce benzoic acid.

Syntheses

The methylium cation (CH3+) can be formed using an effective leaving group in a SN2 reaction, such as methyl iodide, MeI or methyl tosylate, MeOTs.

The methanide anion (CH3-), also known as carbanide is highly unstable and an extremely strong base. Grignard reagents or organolithium reagent can be considered to be mostly ionic and act as alkyl anions. Methanide is not to be confused with methanetetraide (carbide), which is completely depronotoned methane. An example of a methanide is the highly reactive, lithium methanide.

Methyl radical

The methyl radical is the substance CH3 on its own, with an unpaired electron. Though it readily dimerizes to ethane, it is stable enough (unlike atomic hydrogen) to be observed as a dilute gas. It can be produced by thermal decomposition of certain compounds, especially those with an -N=N- linkage, which lose the extremely stable dinitrogen molecule on heating.

Etymology

French chemists Jean-Baptiste Dumas and Eugene Peligot, after determining methanol's chemical structure, introduced "methylene" from the Greek methy = "wine" + hȳlē = wood (patch of trees) with the intention of highlighting its origins, "alcohol made from wood (substance)." The term "methyl" was derived in about 1840 by back-formation from methylene, and was then applied to describe "methyl alcohol."

See also