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Microwave Spectrum of Hydrogen Bonded Hexafluoroisopropanolwater Complex

Abhishek ShahiProf. E. Arunan GroupDepartment of Inorganic and Physical ChemistryIndian Institute of ScienceBangalore-12, India.OutlineIntroduction to the monomers and the complexGuess geometry and structure optimizationSpectrum of complex and its isotopologuesAssignment and DiscussionNature of interactionConclusion

Complex under StudyHFIPWaterHFIP : HexaFluoroIsoPropanol

Water : H2OIntroduction: HFIP-monomerTwo 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), 265274Rotational Spectroscopy of monomerComplete 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

SCAbhishek Shahi and E. Arunan, Colloquium. and OSU-2013, http://hdl.handle.net/1811/55298MonomerOne of the most important molecules for life.A good H-bond acceptor as well as donor.Point Group: C2v.Two non-equivalent lone pairs.

ClustersExperimentally observed up to decamer.Titled complex always competed with water dimer.

Introduction: Water

Binary aqueous solution of HFIP (fluoroalcohol) stabilizes -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, 883-884, 195.Yoshida, K.; Yamaguchi, T. Chem. Phys. 2003, 119, 61326142.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 H2O complex: Properties ,usefulness and past studiesHFIP offers many possibilities for intermolecular interaction.Guess geometries and Structure optimization

Different possible structures were considered for the optimization, which converged to three minima.HFIPSurface minimakcal/mol13-614-615-616*-1917-718-619-620-6Surface maxima2115222023*3624*562515

38 kcal/mol46 kcal/mol46 kcal/mol

B3LYP/6-31G*

MP2/6-311++G**Monomer studies:SC conformer does not exist in supersonic expansions.

These structures have high binding energy but there is conformational instability34 kJ/mol38 kJ/mol0.6 kJ/mol29 kJ/mol34 kJ/molGuess geometries and Structure optimizationMD 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 optimizationAt LC-wPBE/6-311++G**Structure 1Structure 2Binding Energy(kJ/mol)31.817.6Dipole moment(a,b, c) in Debye0.5, 1.8, 1.51.9, 0.2, 1.5Rotational Constants (A, B, C) in MHz1147.98 986.89 709.221053.48 980.63 676.240.270.61The 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