Methyl group

Key takeaways

Methyl group belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Methyl group to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Methyl group from memory before moving on to harder problems.

Reference excerpt

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 (whereas normal methane has the formula CH4). 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 (−CH3), it can be found on its own in any of three forms: methanide anion (CH−3), methylium cation (CH+3) or methyl radical (CH•3). The anion has eight valence electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed.

Methyl cation, anion, and radical

Methyl cation

The methylium cation (CH+3) exists in the gas phase, but is otherwise not encountered. Some compounds are considered to be sources of the CH+3 cation, and this simplification is used pervasively in organic chemistry. For example, protonation of methanol gives an electrophilic methylating reagent that reacts by the SN2 pathway:

CH3OH + H+ → [CH3OH2]+ Similarly, methyl iodide and methyl triflate are viewed as the equivalent of the methyl cation because they readily undergo SN2 reactions by weak nucleophiles. The methyl cation has been detected in interstellar space.

Methyl anion The methanide anion (CH−3) exists only in rarefied gas phase or under exotic conditions. It can be produced by electrical discharge in ketene at low pressure (less than one torr) and its enthalpy of reaction is determined to be about 252.2 ± 3.3 kJ/mol. It is a powerful superbase; only the lithium monoxide anion (LiO−) and the diethynylbenzene dianions are known to be stronger. In discussing mechanisms of organic reactions, methyl lithium and related Grignard reagents are often considered to be salts of CH−3; and though the model may be useful for description and analysis, it is only a useful fiction. Such reagents are generally prepared from the methyl halides:

2 M + CH3X → MCH3 + MX where M is an alkali metal.

Methyl radical

The methyl radical has the formula CH•3. It exists in dilute gases, but in a more concentrated form it readily dimerizes to ethane. It is routinely produced by various enzymes of the radical SAM and methylcobalamin varieties.

Reactivity The reactivity of a methyl group depends on the adjacent substituents. Methyl groups can be quite unreactive. For example, in organic compounds, the methyl group resists attack by even the strongest acids.

Oxidation The oxidation of a methyl group occurs widely in nature and industry. The oxidation products derived from methyl are hydroxymethyl group −CH2OH, formyl group −CHO, and carboxyl group −COOH. For example, permanganate often converts a methyl group to a carboxyl (−COOH) group, e.g. the conversion of toluene to benzoic acid. Ultimately oxidation of methyl groups gives protons and carbon dioxide, as seen in combustion.

Methylation

Demethylation (the transfer of the methyl group to another compound) is a common process, and reagents that undergo this reaction are called methylating agents. Common methylating agents are dimethyl sulfate, methyl iodide, and methyl triflate. Methanogenesis, the source of natural gas, arises via a demethylation reaction. Together with ubiquitin and phosphorylation, methylation is a major biochemical process for modifying protein function. The field of epigenetics focuses on the influence of methylation on gene expression.

Deprotonation Certain methyl groups can be deprotonated. For example, the acidity of the methyl groups in acetone ((CH3)2CO) is about 1020 times more acidic than methane. The resulting carbanions are key intermediates in many reactions in organic synthesis and biosynthesis. Fatty acids are produced in this way.

Free radical reactions When placed in benzylic or allylic positions, the strength of the C−H bond is decreased, and the reactivity of the methyl group increases. One manifestation of this enhanced reactivity is the photochemical chlorination of the methyl group in toluene to give benzyl chloride.

Chiral methyl In the special case where one hydrogen is replaced by deuterium (D) and another hydrogen by tritium (T), the methyl substituent becomes chiral. Methods exist to produce optically pure methyl compounds, e.g., chiral acetic acid (deuterotritoacetic acid CHDTCO2H). Through the use of chiral methyl groups, the stereochemical course of several biochemical transformations have been analyzed.

Rotation

A methyl group may rotate around the R−C axis. This is a free rotation only in the simplest cases like gaseous methyl chloride CH3Cl. In most molecules, the remainder R breaks the C∞ symmetry of the R−C axis and creates a potential V(φ) that restricts the free motion of the three protons. For the model case of ethane CH3CH3, this is discussed under the name ethane barrier. In condensed phases, neighbour molecules also contribute to the potential. Methyl group rotation can be experimentally studied using quasielastic neutron scattering.

Etymology French chemists Jean-Baptiste Dumas and Eugene Peligot, after determining methanol's chemical structure, introduced "methylene" from the Greek μέθυ (methy) "wine" and ὕλη (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" (which since 1892 is called "methanol"). Methyl is the IUPAC nomenclature of organic chemistry term for an alkane (or alkyl) molecule, using the prefix "meth-" to indicate the presence of a single carbon.

Worked examples

Example 1 — a first encounter with Methyl group

Start with the simplest possible case. Write down what Methyl group claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Methyl group before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Methyl group ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Methyl group

In research: Methyl group appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Methyl group in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Methyl group is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkyl groups, Functional groups, so understanding it makes those chapters shorter.
In everyday life: Look for Methyl group outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Methyl group in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Methyl group means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Methyl group out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Methyl group in simple terms?

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 (whereas normal methane has the formula CH4). In formulas, the group is often abbreviated as Me.

Why does Methyl group matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Methyl group?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Methyl group.