methyl

 

(mĕth'əl) , CH₃, organic free radical or alkyl group derived from methane by the removal of one hydrogen atom.

In chemistry, a methyl group is a hydrophobic alkyl functional group derived from methane (CH₄). It has the formula -CH₃ and is very often abbreviated as -Me in the structure of a molecule. This hydrocarbon unit can be found in many organic compounds. It is customarily written as H₃C when on the left of a bond; for example, ethane is represented as H₃C-CH₃.

Methyl groups can be incorporated in organic compounds by an S_N2 reaction on iodomethane, or by the reaction of methyl lithium or MeMgCl with a carbon atom that is substituted with a leaving group.

See also: methylation

Reactivity

The introduction of methyl groups as new substituents in a compound usually increases the lipophilicity of the compound and reduces its water solubility. It should improve the ease of absorption of the analogue into a biological membrane but will make its release from biological membranes into the aqueous media more difficult. The incorporation of a methyl group can have one of three general effects on the rate of metabolism of an analogue:

1. an increased rate of metabolism due to oxidation of the methyl group
2. an increase in the rate of metabolism due to demethylation by the transfer of the methyl group to another compound, or a reduction of the analogue.

Chemically, the reactivity of a methyl group depends partially on what it is attached to. For example, when a methyl group is part of an alkane, it is extremely unreactive and resists all but the strongest of acids, bases, oxidizing agents, and reducing agents. However, in the compound toluene, C₆H₅CH₃, the methyl group is considerably more reactive due to the electron donating abilities 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), which produces benzoic acid.

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 a -N=N- linkage, which lose the extremely stable dinitrogen molecule on heating.

See also

• methanol history for the etymology of methyl

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