Hamburg 2009 – scientific programme
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MO: Fachverband Molekülphysik
MO 24: Elektronische Spektroskopie
MO 24.6: Talk
Friday, March 6, 2009, 12:00–12:15, VMP 6 HS-G
Resonance Raman investigations of a series of differently substituted borols — •Juliane Köhler1, Sonja Lindenmeier1, Ingo Fischer1, Holger Braunschweig2, and Thomas Kupfer2 — 1Institut für Physikalische Chemie, Am Hubland, 97074 Würzburg, Germany — 2Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany
Unsaturated boron-containing heterocycles are of great interest due to their electronic structure. In particular borols, the boron analogues of the cyclopentadienyl cation, are prototypes for the theory of antiaromaticity. In these systems the empty pz-orbital at the boron interacts with the π-system at the carbon backbone to delocalize the four π-electrons. However, this interaction depends on the substituents at the boron-atom. We studied a series of four differently substituted borols by Resonance Raman (RR) spectroscopy. It was our aim to get insight into the structural changes upon π−π*-excitation in the five-membered BC4 ring. In addition, we used DFT calculations to determine the vibrational frequencies. In all compounds the observed vibrational bands indicate an expansion of the borol ring upon electronic exitation. Another significant mode in the spectra gave evidence that the degree of antiaromaticity in the borol depends strongly on the interaction of the substituent at the boron atom with the empty pz-orbital of the boron. Furthermore, we studied the dependence of the excitation wavelenght on the Raman intensities.