Radicals in chemistry are atomic particles that have certain features associated with the transition between compounds. In this article we will get acquainted with the representatives of radicals, their definition and features, and also pay attention to their species diversity.
Introduction
A radical in chemistry is an atom or its group, which is capable of passing, without undergoing changes, from one combination of a compound to another. A similar definition was used by A. L. Lavoisier, who created it himself.
According to Lavoisier, it was assumed that each acid is formed by two simple and indecomposable substances - oxygen and an acid radical. According to this view, it was assumed that sulfuric acids are created by oxygen and sulfur. However, in those days, the difference between acid anhydride and the actual acid was not yet known.
Theory creation
The theory of radicals in chemistry was one of the leading ones in chemistry in the first half of the 19th century. It is based on the idea of A. L. Lavoisier on the importance of oxygen atoms in chemical teaching and the dualistic form of chemical composition. compounds. He, using the "radical" as a terminological unit, expressed his thoughts. They affected the structural features of organic and inorganic acids. The latter, in his opinion, were formed from oxygen and simple radicals (from the 1st element). Organic acids are substances combined by the interaction of O 2 and complex radicals (compound C and H).
After cyan was discovered and an analogy was drawn between some cyanides and chlorides, the understanding of complex radicals improved and strengthened. They began to be defined as atoms that did not change during the transition from the 1st compound to the 2nd. I. Bartzelitsus supported this view with his authoritative opinion. Another important step towards understanding these substances was the proposal to consider wine alcohol and ether as an “esterin” hydrate. They admitted a similar point of view of J. Dumas and P. Bull.
Radicals in chemistry are substances that do not undergo changes during transitions. The theory that was created to describe them in the 1840-50s was gradually replaced by type theory. The change was associated with the presence of a considerable number of factors that were contradictory described by TR.
Organism and radicals
Free radicals in the body are particles that have one or more unpaired electrons located on the outer shell of the electrons. In another definition, a free radical is described as a molecule or atom capable of supporting independent existence. It has some stability and 1 - 2 electrons (e - ) in an unpaired state. Particles e - occupy the orbital of a molecule or atom in a single form. The presence of paramagnetic properties is characteristic of radicals, which is explained by the interaction of an electron with magnetic fields. There are cases in which the presence of e - in an unpaired form entails a significant increase in reactivity.
Examples of free radicals are oxygen molecules (O 2 ), nitric oxide with different valencies (NO and NO 2 ), and chlorine dioxide (ClO 2 ).
Organics
Organic radicals are ionic particles that are characterized by the simultaneous presence of an unpaired electron and charge. Most often, in reactions of organic chemistry, radical ions are created due to the occurrence of one-electron transfers.
If oxidation proceeds in a single-electron form and is applicable to a neutral molecule with an excess of electron density, then it will lead to the creation of a radical cation. The opposite course of the process, during which the neutral molecule is restored, leads to the formation of an anion radical.
A number of aromatic hydrocarbons from the multicore group can independently form both types of radical ions (organic) without much effort.
Free radicals in chemistry are extremely diverse substances, both in their structure and properties. They can be in different states of aggregation, for example, liquid or gas. Their lifespan or the number of electrons that have remained unpaired may also vary. Conventionally, each radical can be attributed to one of two groups: -p- or s-electronic. They differ in the location of the unpaired e - . In the first case, the negative particle occupies a position on the 2p orbitals in the predominant number of cases. The corresponding series of atomic nuclei is in this case located in the nodal orbital plane. In the variant with the s-group, the localization of the electron occurs in such a way that the violation of the electronic configuration practically does not occur.
The concept of hydrocarbon radical
A hydrocarbon radical is an atomic group that forms a bond with a molecular functional group. They are also called hydrocarbon residues. Most often, in the course of chem. radical reactions undergo transitions from one compound to another and do not change. However, such objects of chemical study can carry a number of functional groups. Understanding this forces a person to behave with radicals with extreme caution. Such compounds often include substances that include hydrocarbon residues. The radical itself may be a functional group.
The phenomenon in alkyls
Alkyl radicals are compounds from a number of intermediates that are particles of alkanes. They have free e - in the singular. An example is methyl (CH 3 ) and ethyl (C 2 H 5 ). Several types are distinguished among them: primary (for example, methyl - ▪CH 3 ), secondary (isopropyl - ▪CH (CH 3 ) 2 ), tertiary (tert-butyl ▪C (CH 3 ) 3 ) and quaternary (neopentyl - ▪CH 2 C (CH 3 ) 3 ) a group of alkyl radicals.
Phenomenon in methylene
Methylene radical is the simplest form of carbene. Presented as a colorless gas, and the formula is similar to hydrocarbons from a number of alkenes - CH 2 . The idea of the existence of methylene was put forward in the thirties of the twentieth century, but it was possible to find irrefutable evidence only in 1959. This was done thanks to the spectral research method.
Obtaining methylene became possible due to the use of diazomethane or ketane substances. They are decomposed by UV radiation. During this process, methylene is formed, as well as nitrogen molecules and carbon monoxide.
A radical in chemistry is also a methylene molecule with one carbon atom in which there is no double bond. This distinguishes methylene from alkenes, and therefore it belongs to carbenes. Extreme chemical activity is characteristic of it. The position of electrons can determine various properties of a chemical nature and geometry. There is a singlet (e - - paired) and triplet (electron in a free state - unpaired) form. The triplet form allows one to describe methylene as a biradical.
Hydrophobicity
A hydrophobic radical is a compound having a different polar group. Such molecules and atoms can bond with aminoalkyl sulfo groups via various intermediate bonds.
In accordance with the structure, straight-chain and branched, paraffin (olefin) and perfluorinated radicals are isolated. The presence of a hydrophobic radical allows some substances to easily penetrate through bilayer lipid membranes, as well as integrate into their structures. Such substances are part of non-polar amino acids, which are released due to a certain indicator of the polarity of the side chain.
In the modern method of rational classification of amino acids, radicals are distinguished in accordance with their polarity, i.e., the ability to interact with water in the presence of a physiological pH value (about 7.0 pH). In accordance with the type of radical contained, several classes of amino acids are distinguished: non-polar, polar, aromatic, negatively and positively charged group.
Radicals with hydrophobic properties cause a general decrease in the solubility of peptides. Analogs with hydrophilic qualitative characteristics determine the formation of a hydration shell around the amino acid itself, and peptides dissolve better when interacting with them.