Abstract book - Prof. Per Jensen, Ph.D. - Bergische Universität ...

124 Poster session, H11Structure, Ubbelohde effect, conformational equilibria and tunnelingdynamics of carboxylic acid bi-moleculesGang Feng, Qian Gou, Luca Evangelisti, Walther CaminatiDepartment of Chemistry, University of Bologna, Italy, gang.feng2@unibo.itFeng G.Gou Q.Evangelisti L.Caminati W.Carboxylic acids bi-molecules represent prototype system for investigation of hydrogenbond (HB) interaction and proton transfer. We studied several carboxylic acid bimoleculesin gas phase by using FTMW spectroscopy combine with theoreticalcalculations. As a part of the work, we present here the structure and Ubbelohde effectof acrylic acid (AA)-formic acid (FA), conformational equilibrium and tunnelingdynamics of difluoroacetic acid (DFA) - acrylic acid bi-molecule.Two configurations, cis and trans, of AA-FA have been observed. The rotationalspectra of normal species, 13 C isotopologues in natural abundance and deuteratedspecies were assigned. Thus the full frame structure of the two conformers was obtained.In order to quantify the Ubbelohde effect, we measured the rotational spectra of the 13 Cisotopologues of cis species with one acidic proton deuterated and both deuterated. Wefound that the distance of r(C10C1) increased 10 mÅ while two carboxylic hydrogenwere both deuterated, and increased 8 mÅ while the carboxylic hydrogen of FA wasdeuterated (See Fig. 1A for details).The bi-molecule of DFA-AA can adopt four conformations, with guache or trans DFAinteracting with cis or trans AA. We assigned the rotational spectra of all the fourconformers: TC, GC, TT and GT (see Fig. 1B). From the relative intensity measurement,we found that TC is the most stable conformer, GC, TT and GT has a free energy (ΔG)of 139(50), 516(50) and 523(50) cm -1 higher, respectively. Tunneling splittings havebeen observed for GC and GT conformer. This splitting was induced by the internalrotation of -CF 2 H group. The energy differences of the two tunneling states were foundto be 1.31(1) and 3.2(1) MHz for GC and GT conformer respectively.ABcistransGCGTTCTTFig. 1: Molecular sketch of the AA-FA (A) and DFA-AA (B) bi-molecule calculated withMP2/6-311++G (d, p) level theory.