Conformational Analysis of - PowerPoint Presentation

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Conformational Analysis of R-(+)-3-Methylcyclopentanone by IR Spectroscopy in Para-Hydrogen Crystal

Watheq Al-Basheer1,2, Shin Y. Toh2, Jun Miyazaki2,3 and Takamasa Momose2 1Dep. of Physics, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia 2Dep. of Chemistry, University of British Columbia, Vancouver, BC, Canada 3Dep. of Liberal Arts and Basic Sciences, College of Industrial Technology, niho, japan69th International Symposium on Molecular Spectroscopy University of Illinois at Urbana-Champaign, Jun. 19th 2014

Isolation Matrix Infrared SpectroscopyIn 1954, George C. Pimentel (Berkeley) proposed using inert elements

as isolation matrices due to: 1- Unreactive with entrapped molecule due to completely filled outermost shell 2- Weak forces between atoms (induced p-p) (Van der Waals forces). 3- Electron distribution in crystals close to free atoms (crystals are transparent insulators) 4- Atoms pack as close as possible (fcc structure)

Hydrogen Molecule (H2)

para-hydrogenortho-hydrogen

I = 0

I

= 1

Pure para-Hydrogen (pH

2

) Matrix will work as a good isolation Matrix

Macroscopic View of pH2 as an Isolation Matrix

Hydrogen crystal structure is hexagonal close packed (hcp) which is an ideal isolation matrix due to: 1- Large lattice constant (~ 3.78 ᴼA). 2- Because pH2 is light, it has large zero-point vibration (Amplitude of vibration ~ 20% of the lattice constant). 3- Capability to repair itself of crystal defects. 4- Solvent cage effects are minimalPara-hydrogen crystal is a soft quantum crystal Momose et al, J. Chem. Phys. 107 (19), (1997).

Making & Doping para-hydrogen (pH2) crystal

Candidate dopant molecule (chiral R-(+)-3-Methylcyclopentanone)

R-(+)-3-Methylcyclopentanone (R3MCP) is a chiral ketone.Exists in all living cells (drug industry applications).Has high optical activity.Has enough vapor pressure at room temp. Has two different conformers (Equatorial, Axial).Has 45 vibrational degrees of freedom (possible IR modes [70-3000 cm-1] )W. Al-Basheer, J. Sol. Chem. 41, 1495-1506 (2012)W. Al-Basheer et al, J. Phys. Chem. A. 111(12),(2007)

Para-hydrogen crystal(pH2) Matrix Vs Argon and pure sample

Exp. In pH2 (cm-1)DFT Equatorial(cm-1)DFTAxial(cm-1)664.78 - 662.47721.13 -723.11790.91788.94 - 807.55826.71 -877.09875.82 - 925.42922.05 -935.67936.44 - 987.38988.54 -

Para-hydrogen crystal(pH2) Matrix Vs

Argon and pure sampleExp. In pH2 (cm-1)DFT Equatorial(cm-1)DFTAxial(cm-1)1024.90 - 1021.971133.201125.91 -1147.10 - 1148.011198.90 - 1198.621238.52 - 1236.171266.711267.52 -1286.951287.97 - 1316.82 -1316.101354.901345.95 -1383.361381.70 -1407.201407.62 -1411.01411.17 -1462.38 -1464.911482.921484.49

-

Para-hydrogen crystal(pH2) Matrix Vs

Argon and pure sample

Para-hydrogen crystal(pH2) Matrix Vs

Argon and pure sample

R3MCP concentration in pH2 crystal

R3MCP concentration in pH2 crystal

R3MCP concentration in pH2 crystal

Summary & ConclusionspH2

crystal is an ideal isolation matrix that can yield high resolution IR spectra of molecules due to its intrinsic nature as a cold and soft quantum crystal. Isolation Matrix IR spectroscopy in pH2is an efficient tool to study molecular structure of polyatomic chiral molecules.50 ppm chiral R3MCP molecule concentration in para-hydrogen crystal has yielded the highest resolved IR spectrum. It is possible that pH2 dimers are more likely to form at higher concentrations.

Acknowledgements

KFUPM’s International Summer Scholarly Program (ISSP) for Generous financial supportProf. Takamasa Momose, University of British Columbia for hosting.