Language
Country/Area
No result found
From methane to mysterious substituents: why is the -yl suffix so crucial?
In organic chemistry, a substituent is an atom or group of atoms that replaces one or more atoms, thus becoming part of a new molecule. Although in organic chemistry and biochemistry the terms substituent and functional group used to describe these branches extending from the parent structure are used almost interchangeably, in polymer chemistry there are specific differences. In polymers, side chains extend from the main chain structure, whereas in proteins, side chains are attached to the amino carbon atoms of the amino acid backbone.
When naming organic compounds containing substituents, the suffix -yl is used to indicate the substitution of a hydrogen atom. Similarly, -ylidene and -ylidyne are used to represent the substitution of a double or triple bond. When it is necessary to distinguish between isomers, substituents on hydrocarbons are named using positional numbers to indicate the carbon atom to which the hydrogen atom is replaced. Substituents can exhibit specific properties through combined inductive and resonance effects, which are described as electron enrichment and electron attraction, respectively.
Additional steric effects arise from the volume occupied by the substituents. The terms "most substituted" and "least substituted" are often used to describe or compare molecules that are the products of chemical reactions, using methane as a reference for comparison.
According to this reference, substituting each hydrogen atom causes the molecule to be considered a higher degree of substitution. For example, Markovnikov's law predicts that hydrogen atoms will be added to the carbon atoms of alkene functional groups that possess more hydrogen atoms, while Zazev's law predicts that the primary reaction products are more substituted (stable) double-bonded alkenes.
Naming rules
In organic chemistry, the suffix -yl is used to form the names of free radicals, which can be independent species or chemically bound parts of molecules. It goes back to methanol's old name, "methylene," which was derived from the ancient Greek word for "wine wood," shortened to "methyl," from which -yl was subsequently extracted.
Multiple chemical nomenclature reforms eventually made the use of this suffix universal. According to the 1993 IUPAC recommendation, -yl represents the replacement of a hydrogen atom.
The usage of -ylidene means that two hydrogens are replaced and connected by a double bond, while -ylidyne means that three hydrogens are replaced and connected by a triple bond. The suffix -ylidine appears occasionally and seems to be a variant spelling of "-ylidene" and is not mentioned in the IUPAC guidelines.
Methane substituents
According to the above rules, a carbon atom as a substituent in a molecule will have different names depending on the number of hydrogens attached to it and the type of bond formed. In chemical structural formulas, the symbol R (or R1, R2, etc.) can be used to represent organic substituents. This is a universal placeholder derived from "radical" or "rest" and can replace the part of the formula that the author deems convenient.
Statistically, one study revealed a total of 849,574 unique substituents that contained 12 non-hydrogen atoms and contained only the elements carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorus, selenium, and halogens. There are five common substituents, including methyl, phenyl, chlorine, methoxy and hydroxyl.
In total, the total number of substituents in organic chemistry is estimated to be 3.1 million, creating 6.7×10^23 molecules.
Since an infinite number of substituents can be obtained by increasing the length of the carbon chain, for example, the combination between the substituents methyl (-CH3) and pentyl (-C5H11) will create endless possibilities. The diversity of these substituents demonstrates the richness and complexity of organic chemistry. Does this mean that the way we understand molecules should also change?
