1. 72nd International Symposium on Molecular Spectroscopy, 6/20/2017
CONFORMATIONAL ANALYSIS OF 3,3,3-TRIFLUORO-2-(TRIFLUOROMETHYL) PROPANOIC ACID
JAVIX THOMAS, Department of Chemistry, University of Alberta, Edmonton, AB, Canada;
MICHAEL J CARRILLO, AGAPITO SERRATO III, Department of Chemistry, University of Texas Rio Grande Valley, Brownsville, TX, USA;
ELIJAH G SCHNITZLER, WOLFGANG JÄGER, YUNJIE XU, Department of Chemistry, University of Alberta, Edmonton, AB, Canada;
WEI LIN, Department of Chemistry, University of Texas Rio Grande Valley, Brownsville, TX, USA.
72nd International Symposium on Molecular Spectroscopy, 6/20/2017

2. Only one lower energy conformer detected for perfluorocarboxylic acids
Trifluoroacetic acid
S. Antolinez, J.L. Alonso, H. Dreizler, E. Hentrop, D.H. Sutter; Z. Naturforsch. 54a, 524, (1999)
B. Ouyang, T.G. Starkey, B.J. Howard; J. Phys. Chem. A., 111, 6165 (2007)
Perfluoropropanoic acid
G.S. Grubbs II, A. Serrato III, D. A. Obenchain, S.A. Cooke, S.E. Novick, W. Lin; J. Mol. Spec., 275, 1(2012).
Perfluorobutyric acid
J. Thomas, A. Serrato III, W Lin, W. Jäger, Y. Xu; Chem. Eur. J., 20, 6148, (2014)
Perfluoropentanoic acid
A.M. Pejlovas, W. Lin, S.G. Kukolich; Chem. Phys. Lett., 143, (2015)

3. Comparison of the most stable conformers of the three short chain PFCAs, i.e. trifluoroacetic acid (left), perfluoropropionic acid (middle), and PFBA (right).

4. A potential energy scan of perfluorobutyric acid by rotating carboxyl group about the C1-C2 bond

5. 2,3,3,3-tetrafluoropropanoic acid
Difluoroacetic acid
B.P. van Eijck, A.A.J. Maagdenberg, G. Janssen, T.J. van Goethem-Wiersma;
J. Mol. Spec., 98, 282 (1983)
2 conformers observed
Fluoroacetic acid
B.P. van Eijck, P. Brandts, P.M. Maas; J. Mol. Strc., 44, 1 (1978)
B.P. van Eijck, G. Van der Plaats, P.H. Van Roon;J. Mol. Spec., 11, 67 (1971)
2,3,3,3-tetrafluoropropanoic acid
Lin et al. Investigation ongoing
3 conformers observed
3,3,3-trifluoropropanoic acid
L. Evangelisti, J. van Wijngaarden; J. Mol. Spec., 290, 1 (2013)
One lower energy conformer
4,4,4-trifluorobutyric acid
Yoon Jeong Choi, Alex Treviño, Susanna L. Stephens, Stephen A. Cooke, Stewart E. Novick, Wei Lin; WD04

6. 3,3,3-trifluoro-2-(trifluoromethyl)propanoic acid (TTPA)

7. The microwave spectrometers @Edmonton
Chirped-pulse FTMW spectrometer
Cavity based FTMW spectrometer

8. The Chirped-pulse FTMW spectrometer@Edmonton

9. Experiment
University of Edmonton chirped pulse and cavity based Fourier transform microwave spectrometers;
TTPA(97% Sigma Aldrich) in gas inlet;
Trace amount of TTPA in expansion gas of 3 bar Helium (chirped pulse) and 2 bar Neon (cavity based).

10. Theory Gaussian 09 program package
dihedral angle τ(O12-C5-C2-C1) scan at B3LYP/6-311G level;
Structure optimizations at B3LYP/aug-cc-pVTZ level and MP2/aug-cc-pVTZ level.

11. Potential energy scan along the dihedral angle τ(O12-C5-C2-C1) in steps of 10°
The calculations were done at the B3LYP/6-311G level.

12. Geometries of the four TTPA conformers identified computationally

13. Calculated relative dissociation energies and spectroscopic constants
TTPA-I
TTPA-II
TTPA-III
TTPA-IV
Parameters
B3LYP
MP2
ΔD (kJ/mol)
0.48
0.42
14.3
13.9
23.5
23.0
ΔD0 (kJ/mol)
0.36
0.27
13.6
22.9
22.6
A (MHz)
1063.6
1078.1
1073.5
1087.8
1074.5
1087.5
1129.1
1146.6
B (MHz)
963.0
977.1
962.7
977.2
965.4
979.7
952.6
967.4
C (MHz)
680.5
692.6
684.9
696.6
688.1
699.2
656.9
670.5
µa (Debye)
0.0
2.0
1.8
µb (Debye)
1.9
1.0
1.2
1.3
µc (Debye)
2.2
2.1
0.6
0.5
0.7
2.8

14. A sample spectrum showing the transition of TTPAI and transition of TTPA II from the cavity based measurement.

15. Experimental spectroscopic constants
Parameter
TTPA-I
TTPA-II
A (MHz)
(56)
(37)
B (MHz)
(41)
(34)
C (MHz)
(34)
(21)
ΔJ (kHz)
0.0359(73)
0.0396(60)
ΔJK (kHz)
0.730(31)
0.402(23)
ΔK (kHz)
-0.724(21)
(16)
δJ (kHz)
0.0114(26)
0.0131(27)
δK (kHz)
0.029(10)
(79) N 37 36
σ (kHz)
2.8
1.7

16. Conclusion
The rotational spectrum of TTPA was measured for the first time using both chirped-pulse and cavity-based FTMW spectrometers.
Two conformers were observed experimentally and identified unambiguously. The rotational constants of the observed conformers are in excellent agreement with those from the quantum chemical structures.
Comparison of TTPA and previously reported fluorinated carboxylic acids shows some noticeable differences in their preferred geometries and conformational energetics, such as the interconversion barrier height between the conformers, highlighting the diversity of conformational landscapes in this class of compounds.

18. Acknowledgement Welch Foundation # BX-0048
UTRGV Undergraduate Research Initiative (URI)
The University of Alberta
The Natural Sciences and Engineering Research Council (NSERC) of Canada
YX and WJ are holders of Tier I Canada Research Chairs.
Texas Advanced Computing Center (TACC) and the Shared Hierarchical Academic Research Computing Network (SHARCNET: the Western Canada Research Grid (Westgrid), and Compute/Calcul Canada.