FELIX provides insight into the electronic and geometric stability of molecules
Researchers from the FOM Institute for Plasma Physics Rijnhuizen have provided more clarity about the stability of carbocations. They did this by determining the structure of one of these organic ions with the free electron laser FELIX. Information about electronic and geometric stability is fundamentally important for organic chemistry but can also contribute to knowledge about interstellar gas clouds in the universe. The researchers will publish their results in August in the leading German journal Angewandte Chemie.
Stability in two forms
There are two factors that determine the stability of a carbocation. Firstly, how the electrons are arranged. Electrons form the 'glue' that binds the atoms in a molecule together. The electrons are located in so-called orbitals (three-dimensional wave functions) between the atoms. Normally, the electrons are found in pairs in these orbitals; unpaired electrons give rise to electronic instability. Secondly, there is a geometric stability, which depends on how the atoms in the carbocation are positioned relative to each other.
Infrared spectrum
The researchers from Rijnhuizen have examined the stability of the gaseous carbocation 'naphthyl' (C10H7 +). They did this by recording an infrared spectrum using the free electron laser FELIX. The spectrum provides direct information about the structure and therefore reveals whether the geometric or electronic stability ultimately exerts the most influence on the ion's structure. Although calculations predict that both effects exert an equally large influence, the researchers discovered that the ion prefers geometric stability to electronic stability. Consequently, the ion has a highly geometric symmetry but not all of the electrons are found in pairs. For the smaller carbocation phenyl, the converse is true: electronic stability plays a bigger role.
Interstellar clouds
Using this new information, predictions can also be made about carbocations which are larger than naphthyl. This knowledge is fundamentally important for organic chemistry. Astrochemists are also interested in the results; they hypothesise that this type of molecule frequently occurs in interstellar clouds. These are huge nebulae of gas, plasma and dust in the universe. The composition of these nebulae will provide astrochemists with information about the birth of new stars. The physical form in which these ions occur directly influences their spectroscopic fingerprint (on the basis of which they are detected) and their behaviour in chemical reactions that take place in the nebulae.
Further information
For further information please contact Prof.dr. J. Oomens +31 (0)30 609 67 96.
Reference
The article is now available online:
'Spectroscopic Evidence for a Triplet Ground State in the Naphthyl Cation'
Héctor Alvaro Galué, Jos Oomens