The shortest chemical bond between carbon atoms and chlorine was discovered

A researcher from the Department of Chemistry and Biochemistry at the University of Munich who initially focused on the preparation and testing of new high-energy materials demonstrated for the first time that even secondary and tertiary neighbors may have a decisive effect on the properties of a chemical bond

The description of the structure of compounds and the interrelationships between the atoms that make them up is one of the most fundamental goals in the science of chemistry. Models for chemical bonding, which describe these properties well, already exist in science. However, any deviation from the usual factors may lead to further improvement in these models. Chemists from the University of Munich in Germany have now studied a compound containing an extremely short chemical bond.

As published by the researchers in the scientific journal Nature Chemistry, the carbon atom and the chlorine atom in the compound known as chlorotrinitromethane are only 1.69 angstroms apart. "Noncovalent interactions are one of the factors responsible for this short distance," notes the researcher Göbel, whose doctoral thesis revealed the new findings. "A better understanding of these interactions is important and useful in all areas where molecular recognition and self-assembly are manifested."

Chemical bond models, which have been used with great success for more than a hundred years, assume that it is possible to obtain a proper description of the properties of compounds while ignoring or neglecting the interactions between non-adjacent chemical bonds. The assumption that electrostatic interactions between neighbors separated by two, three or even more bonds are important and cannot be neglected was not widespread until now. The research team of Professor Thomas M. Klapötke from the Department of Chemistry and Biochemistry at the University of Munich (LMU), which initially focused on the preparation and testing of novel high-energy materials, has now demonstrated, for the first time ever, that even secondary and tertiary neighbors may have a decisive influence on the properties of a chemical bond .

For their study, the scientists chose the compound called chlorotrinitromethane which contains a chlorine atom and three nitro groups all bonded to a common carbon atom. The trinitromethane group itself consists of a carbon atom attached to three nitro groups. This unit belongs to the group of substances called pseudo-halogens, which are substances with properties similar to those of the normal halogens. Both groups consist of non-metallic atoms, which normally exist in the liquid or gaseous state and form salts with the metals. However, unlike the halogens, the pseudohalogens are not original atomic elements but rather chemical groups composed of several different components.

Through structural analysis based on X-rays, the researchers were able for the first time ever to reveal the internal structure of the chlorotrinitromethane compound and drew conclusions about the distances between the various atoms.

In their research, the chemists showed that there is an interesting feature in this compound - the distance between the chlorine atom and its carbon atom is only 1.69 angstroms. This distance, now measured, is the shortest ever observed for a single chemical bond between a chlorine atom and a carbon atom. All distances measured so far have been in the range of 1.71 to 1.91 angstroms.

Thanks to theoretical calculations, made in collaboration with Professor Peter Politzer from the University of New Orleans in the USA, the researchers were able to characterize the distribution of electric charges within the insulation. From the findings obtained, it turns out that the chlorine atom has a positive electrostatic potential - a rare case, because chlorine usually has a negative electrostatic potential in other substances. Combined with additional data regarding the distribution of charges in the other atoms, this finding explains why the chlorine and carbon atoms are so closely related to each other. The results of the study show, in an impressive way, that the electrostatic interaction between the atoms that make up the bond may have a significant effect on the lengths of the bonds, even if these atoms are not directly connected to one of the atoms that make up the bond itself.

In the case of the substance examined, this effect is particularly significant and leads to an unusually short chlorine-carbon bond. Moreover, these factors can be extremely important in various other cases, especially in areas where separate entities are required to "know" each other and create complex and larger structures together. These mechanisms play a crucial role, for example, in biological systems and nanotechnology.

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