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Scott Flancher

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Review of halogen bonding -hole Applications Homo-halogen bonding hypothesis Experiments / Data Kinetics 19 F-NMR IR Future research

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Similar to hydrogen bonding Electron density pulled into bond Exposes area of positive potential on extension of bond axis (the -hole)

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Biochemistry Protein recognition Drug design DNA Material Science Crystal engineering Macromolecular engineering Voth A. R. et.al. PNAS 2007;104:6188-6193 Resnati et.al. J. Fluorine Chem. 2004;104: 271

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Originally studied hydrogen bonding using the I (2) CARS method Pyridine a good candidate for studies Strong signal Vibrational modes well characterized Prime choice for the foray into halogen bonding Perfluorinated compounds good for halogen bonding Electron withdrawing nature of fluorines I > Br > Cl > F

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Summer of 2009 I (2) CARS with several iodo-perfluoroalkanes Established presence of strong halogen bonding Thermodynamic studies also shed more light on liquid structure Ultimately led to the homo-halogen bonding hypothesis for 2-iodo perfluoropropane

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-fluorine directed halogen bonding Thought to be more likely in 2-iodo perfluoropropane In 1-iodo perfluoropropane the electron density split by two -fluorines Focused on the 2-iodo perfluoropropane

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To test the homo-halogen bonding hypothesis utilized several techniques Analysis of physical properties 19 F-NMR IR Noticed photochemical dissociation when left in room lights Suggested a kinetics study

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Let cuvettes sit in room light and observed their color change via the following reaction: Measured absorbance every 10 minutes to check iodine production

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Time 20minTime 30minTime 45min Time 60minTime 90minTime 18hrs X=0.2NeatX=0.2NeatX=0.2Neat X=0.2NeatX=0.2Neat X=0.2Neat

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Different rate constants observed k obs = 0.0755min -1 in hexane (after correction for mole fraction) k obs = 0.0019min -1 when neat Iodine production nearly 40x faster in hexane Protection of iodine Dissociation and geminate pair recombination

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Two possibilities: Halogen bond protects the C-I bond from breaking Geminate pair recombination

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Also saw less I 2 production when diluted with pyridine 1-iodo behaved differently Dilution with hexane showed minimal difference in rate of iodine production

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Compare boiling point difference of non- fluorinated to fluorinated: 12C difference compared to 1C difference Compare melting point difference of non- fluorinated to fluorinated: 11C difference compared to 37C difference Skeptical of melting points for perfluorinated compounds CompoundBoiling Point (C) Melting Point C 3 H 7 I (1-iodo) 102-101 C 3 H 7 I (2-iodo) 90-90 C 3 F 7 I (1-iodo) 41-95 C 3 F 7 I (2-iodo) 40-58

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C- F stretch Uncharacterized vibrational modes

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Gives compelling evidence for presence of two species in neat 2-iodo perfluoropropane Lack of complete mode assignment Still shows peak broadening Suggests a different species is present

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19 F-NMR -peak and -peak behavior Measures amount of electron shielding

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More shielding Less shielding Halogen bonding

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More shielding Less shielding

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When diluted with pyridine, -fluorine becomes more shielded Electron density from pyridine pulled to -fluorine Chemical shift remains relatively stagnant when majority of solution is pyridine

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More shielding Less shielding Halogen bonding

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More shielding Less shielding Halogen bonding

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Dilution studies When diluted with cyclohexane, less proclivity for homo-halogen bonding, therefore less shielding Temperature studies Lower temperatures show greater shielding / greater structuring

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-peak behavior consistent with hypothesis Stronger halogen bond -> greater, negative chemical shift Mixed in neutral solvent (cyclohexane) Showed shifting opposite to that of halogen bond acceptor Temperature studies

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Homo-halogen bonding IR Shift in the -peak Peak broadening indicative of dual-species Boiling and melting points Kinetics Iodine production rates Geminate pair recombination NMR Shift in -peak Shielding levels based on temperature

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Conventional Raman to compliment IR 1-iodo perfluoropropane

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Concordia Chemistry Department and Laser Facility Craig Jasperse and MSUM NMR facility NSF Dreyfus Foundation Concordia College Research Endowment Undergraduate Research, Scholarly and Creative Activities Grant Program Dr. Ulness, Dr. Gealy