Frankfurt 2006 – scientific programme
Parts | Days | Selection | Search | Downloads | Help
MO: Molekülphysik
MO 24: High Resolution Spectroscopy
MO 24.8: Talk
Tuesday, March 14, 2006, 15:45–16:00, H10
The C2v Structure of Acetylacetone — •Jens-Uwe Grabow1 and Walther Caminati2 — 1Universität Hannover, Institut für Physikalische Chemie und Elektrochemie, Callinstr. 3-3A, D-30167 Hannover — 2Dipartimento di Chimica ¨G. Ciamician¨ dell’Università, Via Selmi 2, I-40126 Bologna, Italien
Acetylacetone allows for several tautomeric forms at different conformations in dynamic equilibrium and multiple pathways of internal motions between equivalent configurations; together with malonaldehyde it can be considered a prototype molecule for studying keto-enol tautomerization. We present here the pure rotational spectrum of enolic acetylacetone, measured in supersonic expansions, which provides strong evidence for the symmetric nature of the internally highly dynamic molecule.
It has often be postulated that the lowest energy enolic form of Acetylacetone assumes Cs symmetry, i.e., has a double-minimum potential possibly exhibiting a low barrier to internal proton transfer and not a single minimum, C2v. Recent theoretical calculations and experimental work support the Cs hypothesis but the literature on this fascinating molecule is divided. Towards this objective, the high-resolution rotational spectra of enolic acetylacetone and 3 isotopologues have been obtained, revealing C2v symmetry. The two methyl groups exhibit a very low barrier to internal rotation, thus making acetylacetone internally highly dynamic.