Conformational Equilibria and Large‐Amplitude Motions in Dimers of Carboxylic Acids: Rotational Spectrum of Acetic Acid–Difluoroacetic Acid |
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Authors: | Qian Gou Dr Gang Feng Dr Luca Evangelisti Prof Walther Caminati |
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Institution: | Dipartimento di Chimica “G. Ciamician”, Università di Bologna, Via Selmi 2, I‐40126 Bologna (Italy), Fax: (+39)?0512099456 |
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Abstract: | We report the rotational spectra of two conformers of the acetic acid–difluoroacetic acid adduct (CH3COOH–CHF2COOH) and supply information on its internal dynamics. The two conformers differ from each other, depending on the trans or gauche orientation of the terminal ?CHF2 group. Both conformers display splittings of the rotational transitions, due to the internal rotation of the methyl group of acetic acid. The corresponding barriers are determined to be V3(trans)=99.8(3) and V3(gauche)=90.5(9) cm?1 (where V3 is the methyl rotation barrier height). The gauche form displays a further doubling of the rotational transitions, due to the tunneling motion of the ?CHF2 group between its two equivalent conformations. The corresponding B2 barrier is estimated to be 108(2) cm?1. The increase in the distance between the two monomers upon OH→OD deuteration (the Ubbelohde effect) is determined. |
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Keywords: | conformational equilibria hydrogen bonds internal dynamics rotational spectroscopy ubbelohde effect |
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