Microwave Spectrum of Hydrogen Bonded Hexafluoroisopropanol  water Complex Abhishek Shahi Prof. E. Arunan Group Department of Inorganic and Physical Chemistry Indian Institute of Science Bangalore-12, India.

Outline Introduction to the monomers and the complex Guess geometry and structure optimization Spectrum of complex and its isotopologues Assignment and Discussion Nature of interaction Conclusion

Complex under Study HFIPWater HFIP : HexaFluoroIsoPropanolWater : H 2 O

Introduction: HFIP-monomer Two conformers at room temperature (IR studies). Anti-periplanar (AP) is more stable than Synclinical (SC) in gas phase. Suhm M. Journal of Physical Chemistry A, 2000, 104(2), 265–274 Rotational Spectroscopy of monomer Complete structural determination of monomer. Microwave spectrum of 6 isotopologues (parent, two deuterated, three C-13) Only AP conformer could be seen in supersonic expansion. AP SC Abhishek Shahi and E. Arunan, Colloquium. and OSU-2013,

Monomer One of the most important molecules for life. A good H-bond acceptor as well as donor. Point Group: C 2v. Two non-equivalent lone pairs. Clusters Experimentally observed up to decamer. Titled complex always competed with water dimer. Introduction: Water

Binary aqueous solution of HFIP (fluoroalcohol) stabilizes α -helical structure of protein. HFIP is a commonly used solvent for dissolving polymer such as polyethylene terephthalate (PET), a normally difficult-to-dissolve polymer. HFIP can act as both H-bond donor as well as acceptor. IR, Raman, X-ray, NMR, MD simulation Studies are known for the HFIPwater complexes in liquid and gas phase. These studies suggest a very strong bond between HFIP and water. Czarnik-Matusewicz, B.; Pilorz, S.; Zhang, L.-P.; Wu, Y. J. Mol. Struct. 2008, , 195. Yoshida, K.; Yamaguchi, T. Chem. Phys. 2003, 119, 6132–6142. N. Hirota-Nakaoka and Y. Goto, Bioorg. Med. Chem. 1999, 7,67. R. Rajan and P. Balaram, Int. J. Pept. Protein Res. 1996, 48, 328. Introduction to the HFIP    H 2 O complex: Properties,usefulness and past studies

HFIP offers many possibilities for intermolecular interaction. Guess geometries and Structure optimization Different possible structures were considered for the optimization, which converged to three minima. HFIP Surface minima kcal/mol * Surface maxima *36 24* kcal/mol 46 kcal/mol

B3LYP/6-31G* MP2/ G** Monomer studies: SC conformer does not exist in supersonic expansions. These structures have high binding energy but there is conformational instability 34 kJ/mol38 kJ/mol 0.6 kJ/mol 29 kJ/mol 34 kJ/mol Guess geometries and Structure optimization

MD studies suggest one more minimum for the HFIPwater complex. Exhibits two H-bonding interactions. C-H group acts as hydrogen bond donor. Formation of five-membered ring. AP conformer of HFIP is involved. Therefore, finally two structures were considered for the search of rotational transitions. Guess geometries and Structure optimization

At LC-wPBE/ G**Structure 1Structure 2 Binding Energy (kJ/mol) Dipole moment ( μ a, μ b, μ c ) in Debye 0.5, 1.8, , 0.2, 1.5 Rotational Constants (A, B, C) in MHz  The two most stable structures and their properties

On the basis of calculated rotational constants, search was started for following sets of lines. At the end, 46 transitions were observed and could be fitted within experimental uncertainty using a semi-rigid rotor Hamiltonian. TransitionsCalculated (MHz)Observed (MHz) 5, 0, 5 <-- 4, 1, , 1, 5 <-- 4, 0, , 0, 6 <-- 5, 1, , 1, 6 <-- 5, 0, , 0, 7 <-- 6, 1, , 1, 7 <-- 6, 0, , 0, 8 <-- 7, 1, , 1, 8 <-- 7, 0, Search for rotational transitions

TransitionsObservedObs-Calc 2, 0, 2 <- 1, 1, , 1, 2 <- 1, 0, , 0, 3 <- 2, 1, , 1, 3 <- 2, 0, , 0, 4 <- 3, 1, , 1, 4 <- 3, 0, , 0, 5 <- 4, 1, , 1, 5 <- 4, 0, , 2, 4 <- 4, 1, , 2, 3 <- 4, 3, , 4, 1 <- 3, 3, , 4, 0 <- 3, 3, , 0, 6 <- 5, 1, , 1, 6 <- 5, 0, , 4, 1 <- 3, 3, , 0, 8 <- 7, 1, , 1, 8 <- 7, 0, , 3, 4 <- 6, 4, , 1, 7 <- 7, 2, , 2, 7 <- 7, 1, , 0, 9 <- 8, 1, , 1, 9 <- 8, 0, , 0, 10 <- 9, 1, , 1, 10 <- 9, 0, , 3, 1 <- 3, 2, , 3, 3 <- 4, 2, , 1, 5 <- 5, 2, , 2, 5 <- 5, 1, , 2, 4 <- 5, 3, , 0, 7 <- 6, 1, , 1, 7 <- 6, 0, , 4, 2 <- 4, 3, , 3, 2 <- 4, 2, , 3, 4 <- 5, 2, , 2, 3 <- 4, 1, , 1, 4 <- 4, 0, , 4, 1 <- 4, 3, , 2, 4 <- 4, 1, , 3, 3 <- 4, 2, , 4, 2 <- 4, 3, , 1, 6 <- 6, 2, , 2, 6 <- 6, 1, , 5, 1 <- 4, 4, , 5, 0 <- 4, 4, , 5, 1 <- 4, 4, , 5, 0 <- 4, 4, b-type signals were stronger than c-type. a-type signals were absent. Kisiel’s programs were used for fitting.

Experimental Calculated Structure 1 Calculated Structure 2 A/MHz (77) B/MHz (44) C/MHz (20) D J /kHz (51) D JK /kHz 2.230(39) D K /kHz (29) d 1 /kHz (27) d 2 /kHz (18) RMS (MHz) No. of transitions 46 b- & c-type only Dipole Moment b-type transitions were stronger than c-type 0.5, 1.8, , 0.2, 1.5 No a-type transitions (WHY ?) Results and comparisons with theory

I.HFIPD 2 O II.HFIPHOD Two isotopologues could be observed Isotopologues Sample preparation of HOD by mixing H 2 O and D 2 O in 1:1 ratio

HFIPH 2 O Parent HFIPD 2 O (I) HFIPHOD (II) A /MHz (77) (10) (67) B /MHz (44) (16) (17) C /MHz (20) (22) (21) D J /kHz (51) (25) (74) D JK /kHz 2.230(39) 2.43(16) 3.526(89) D K /kHz (29) -1.91(14) (86) d 1 /kHz (27) 0.029(11)[0.0092] d 2 /kHz (18) (57) (39) RMS /MHz Transition Both the hydrogens of water are identical. Rotational Constants of the isotopologues

Both hydrogens are identical ! Vib. Freq. 75 cm-1 ZPE = 0.46 kJ/mol Barrier Height = 0.24 kJ/mol Absence of a-type transition

Exp= (83) Å Kraitchman’s analysis and the ‘experimental’ structure

18 Exp= (70) Å DistancesExperimentalStructure 1Structure 2 CM-H (83) Å CM-H (70) Å Kraitchman’s analysis and the ‘experimental’ structure

Theoretical prediction ExperimentStrucure 1Cal-ExpStrucutre 2Cal-Exp HFIP---H 2 O HFIP---HOD HFIP---D 2 O

ExperimentMP2mp2=fullb2plypB2plypdLC-wPBECAM-B3LYPwB97XD A (77) B (44) C (20) D J (51) D JK 2.230(39) D K (29) d (27) d (18) Which one is better ? Ab initio Calculations

A very strong Hydrogen Bonding Structure 1 Structure 2 AIM analysis There is linear correlation between Electron density at intermolecular BCP (green dots) and binding energy

One H-bond in Structure 1 Overlapping of Oxygen’s lone pair of water with O-H(  *) of HFIP stabilize the complex by 21.2 kcal/mol. Two H-bonds in Structure 2 Overlapping of Oxygen’s lone pair of water with C-H(  *) of HFIP stabilize the complex by 1.8 kcal/mol. Overlapping of Oxygen’s lone pair of HFIP with O-H(  *) of HFIP stabilize the complex by 0.88 kcal/mol. NBO analysis A very strong Hydrogen Bonding

Rotational spectra of HFIP---water and its two isotopologues have been observed and fitted within experimental uncertainty. The fitted rotational constants confirm that the HFIP---water complex exists as structure 1. A very strong H-bounded complex. Summary

Acknowledgements: All labmates. Funding: