The first experimental observation of the higher-energy trans conformer of trifluoroacetic acid

被引:15
作者
Apostolo, R. F. G. [1 ]
Bazso, Gabor [2 ]
Bento, R. R. F. [1 ,3 ]
Tarczay, G. [2 ]
Fausto, R. [1 ]
机构
[1] Univ Coimbra, Dept Chem, CQC, P-3004535 Coimbra, Portugal
[2] Eotvos Lorand Univ, Dept Inorgan Chem, H-1117 Budapest, Hungary
[3] Univ Fed Mato Grosso, Inst Fis, BR-78060900 Cuiaba, Brazil
基金
匈牙利科学研究基金会;
关键词
Trifluoracetic acid; NIR-Induced in situ generation of trans-TFA; Tunneling decay rates; Matrix-isolation IR spectroscopy; Quantum chemical calculations; CORRELATED MOLECULAR CALCULATIONS; INFRARED MATRIX-ISOLATION; GAUSSIAN-BASIS SETS; FORMIC-ACID; ACETIC-ACID; VIBRATIONAL SPECTROSCOPY; ROTATIONAL-ISOMERISM; TUNNELING LIFETIME; HYDROGEN-BOND; MP2; ENERGY;
D O I
10.1016/j.molstruc.2016.06.077
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We report here the first experimental observation of the higher-energy conformer of trifluoroacetic acid (trans-TFA). The new conformer was generated by selective narrowband near-infrared vibrational excitation of the lower-energy cis-TFA conformer isolated in cryogenic matrices (Ar, Kr, N-2) and shown to spontaneously decay to this latter form in the various, matrix media, by tunneling. The decay rates in the different matrices were measured and compared with those of the trans conformers of other carboxylic acids in similar experimental conditions. The experimental studies received support from quantum chemistry calculations undertaken at various levels of approximation, which allowed a detailed characterization of the relevant regions of the potential energy surface of the molecule and the detailed assignment of the infrared spectra of the two conformers in the various matrices. Noteworthly, in contrast to cis-TFA that has its trifluoromethyl group eclipsed with the C=O bond of the carboxylic moiety, trans-TFA has the trifluoromethyl group eclipsed with the C-O bond. This unusual structure of trans-TFA results from the fact that the relative orientation of the CF3 and COOH groups in this geometry facilitates the establishment of an intramolecular hydrogen-bond-like interaction between the OH group and the closely located in-plane fluorine atom of the CF3 moiety. (C) 2016 Elsevier B.V. All rights reserved.
引用
收藏
页码:288 / 295
页数:8
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