The methyl or methyl group is an alkyl substituent whose chemical formula is CH3. It is the simplest of all the carbon substituents in organic chemistry, it has a single carbon and three hydrogens; derives from methane gas. Because it can only bind to another carbon, its position indicates the end of a chain, its termination.
In the image below there is one of the many representations for this group. The curves to its right indicate that behind the H link3C- can be any atom or substituent; an alkyl, R, aromatic or aryl, Ar, or a heteroatom or functional group, such as OH or Cl.
When the functional group attached to the methyl is OH, we have the alcohol methanol, CH3OH; and if it is Cl, then we will have methyl chloride, CH3Cl. In organic nomenclature it is referred to simply as 'methyl' preceded by the number of its position in the longest carbon chain.
The methyl group CH3 is easy to identify during elucidations of organic structures, especially thanks to carbon 13 nuclear magnetic resonance spectroscopy (C NMR13). From it, after strong oxidations, COOH acid groups are obtained, being a synthetic route to synthesize carboxylic acids.
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Above we have the four possible representations assuming that the CH3 is linked to an alkyl substituent R. All are equivalent, but while going from left to right the spatial aspects of the molecule are evident.
For example, R-CH3 it gives the impression that it is flat and linear. The representation that follows shows the three C-H covalent bonds, which allow the methyl to be identified in any Lewis structure and give the false impression of being a cross..
Then, continuing to the right (the penultimate), the sp hybridization is observed3 on the carbon of CH3 because of its tetrahedral geometry. In the last representation, the chemical symbol for carbon is not even written, but the tetrahedron is kept to indicate which H atoms are in front of or behind the plane..
Although it is not in the image, another very recurrent way when representing the CH3 it consists of simply placing the hyphen (-) “naked”. This is very useful when drawing large carbon skeletons..
The top image is the three-dimensional representation of the first one. The glossy black sphere corresponds to the carbon atom, while the white ones are the hydrogen atoms.
Again, carbon has a tetrahedral environment product of its sp hybridization3, and as such it is a relatively bulky group, with its C-R bond rotations sterically hindered; that is, it cannot rotate because the white spheres would interfere with the electronic clouds of their neighboring atoms and feel their repulsion.
However, the C-H bonds can vibrate, just like the C-R bond. Therefore, the CH3 is a group of tetrahedral geometry that can be elucidated (determined, ascertained) by infrared radiation (IR) spectroscopy, like all functional groups and carbon bonds with heteroatoms.
The most important thing, however, is its elucidation by C-NMR.13. Thanks to this technique, the relative amount of methyl groups is determined, which allows the molecular structure to be assembled..
Generally, the more CH groups3 have a molecule, the more "clumsy" or inefficient will be its intermolecular interactions; that is, the lower their melting and boiling points will be. CH groups3, due to their hydrogens, they “slide” against each other when approaching or touching.
The methyl group is characterized by being essentially hydrophobic and apolar.
This is because their C-H bonds are not very polar due to the low difference between the electronegativities of carbon and hydrogen; Furthermore, its tetrahedral and symmetric geometry distributes its electron densities almost homogeneously, which contributes to a negligible dipole moment..
In the absence of polarity, the CH3 It "runs away" from water, behaving like a hydrophobe. Therefore, if it is seen in a molecule, it will be known that this methyl end will not interact efficiently with water or another polar solvent..
Another feature of the CH3 is its relative stability. Unless the atom that is bonded to it removes its electronic density, it remains practically inert against very strong acidic media. However, it will be seen that it can participate in chemical reactions, mainly with regard to its oxidation, or migration (methylation) to another molecule.
The CH3 it is not exempt from rusting. This means that it is susceptible to forming bonds with oxygen, C-O, if it reacts with strong oxidizing agents. As it oxidizes, it transforms into different functional groups.
For example, its first oxidation gives rise to the methiol (or hydroxymethyl) group, CHtwoOH, an alcohol. The second derives in the formyl group, CHO (HC = O), an aldehyde. And the third, finally, allows its conversion into the carboxyl group, COOH, a carboxylic acid.
This series of oxidations is used to synthesize benzoic acid (HOOC-C6H5) from toluene (H3DC6H5).
The CH3 during the mechanism of some reactions it can gain momentary electrical charges. For example, when methanol is heated in a very strong acid medium, in the theoretical absence of nucleophiles (seekers of positive charges), the methyl cation, CH3+, since the CH bond is broken3-OH and the OH leaves with the electron pair of the bond.
The species CH3+ it is so reactive that it has only been determined in the gas phase, since it reacts or disappears at the slightest presence of a nucleophile.
On the other hand, the CH3 an anion can also be obtained: methanide, CH3-, the simplest carbanion of all. However, like the ch3+, its presence is abnormal and only occurs in extreme conditions.
In the methylation reaction, a CH is transferred3 to a molecule without producing electric charges (CH3+ nor CH3-) in the process. For example, methyl iodide, CH3I, is a good methylating agent, and can replace the O-H bond of several molecules with an O-CH3.
In organic synthesis this does not entail any tragedy; but yes when what is methylated in excess are the nitrogenous bases of DNA.
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