Homo-halogen Bonding in 2-iodo-perfluoroalkane Darin J. Ulness Department of Chemistry Concordia College, Moorhead, MN

Outline Hydrogen bonding History The s hole and s hole bonding Data Discussion

Hydrogen Bonding Hydrogen on a N, O, F Interact with a N, O, F Bond distance shorter than sum of Van der Waals Radii Angle approximately 180o

Halogen Bonding I > Br > Cl, no F Interact with a N, O Bond distance shorter than sum of Van der Waals Radii Angle approximately 180o

Halogen Bonding: History F. Guthrie, J. Chem. Soc. 16, 239 (1863) Complexation of I2 and NH3 I. Remsen, J.F. Norris, Am. Chem. J. 18, 90, (1896) Complexation of X2 and methyl amines O. Hassel, Proc. Chem. Soc. 7, 250 (1957) [Nobel Prize 1969] Donor/acceptor complexes: Halogens and Lone Pair T. Di Paolo, C. Sandorfy, Can. J. Chem. 52, 3612 (1974) Spectroscopic studies aromatic amines and halo-alkanes

Halogen Bonding: Today Biochemistry Biomolecular engineering Drug Design Materials Science Crystal engineering Molecular recognition Halogen Bonding Computational Chemistry s hole bonding Voth A. R. et.al. PNAS 2007;104:6188-6193 Resnati et.al. J. Fluorine Chem. 2004;104: 271

The s hole Test charge far from an iodine atom Free Iodine Atom Test Charge “feels” an electroneutral field

The s hole I Test charge close to an iodine atom Test Charge “feels” an electropositive field An arbitrary spherical surface carries an eletropositive potential !

The s hole In molecules the electron density is directed into the bond Test Charge In molecules the electron density is directed into the bond

The s hole Electropositve s-hole Electroneutral “ring” Electronegative Test Charge Electroneutral “ring” Electronegative “belt”

The s hole Perfluorinate: Stronger s hole Electropositve s-hole Test Charge Electroneutral “ring” Electronegative “belt”

s hole bonding with pyridine

Pyridine as a probe of Halogen bonding The ring stretches of pyridine act as a probe of its environment C N C N “ring-breathing” mode “triangle” mode

Pyridine as a probe of Halogen bonding Hydrogen bonding to a water modulates the stretching frequency H H O C N N C C C C C free pyridine H-bonded pyridine

I(2)CARS Experiment t Computer CCD Interferometer Monochromator Sample B’ B I(2)CARS M Lens Broadband Source (noisy light) Narrowband Source

Pyridine as a probe

Pyridine as a probe ring-breathing H-bonded pyridine free pyridine

Pyridine as a probe of Halogen bonding 1-iodo-perfluoroalkanes 2-iodo-perfluoropropane C3F7I C6F13I C4F9I

1-iodo-perfluoroalkanes C4F9I C6F13I

2-iodo-perfluoropropane C3F7I C6F13I

Temperature Studies C3F7I C6F13I

1-iodo-perfluoroalkanes I’m Special ! 2-iodo-perfluoropropane 1-iodo-perfluoroalkanes

Conjecture Stronger and more aF directed homo-halogen bonding leads to more local solvent structure order. Increased positive entropy contribution Increased positive enthalpy contribution

One is better than two ?

One is better than two ?

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

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

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

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

Boiling and melting points Compare boiling point difference of non-fluorinated to fluorinated: 12°C difference compared to 1°C difference Compare melting point difference of non-fluorinated to fluorinated: 11°C difference compared to 37°C difference Compound Boiling Point (°C) Melting Point C3H7I (1-iodo) 102 -101 (2-iodo) 90 -90 C3F7I 41 -95 40 -58

Boiling and melting points Compare boiling point difference of non-fluorinated to fluorinated: 12°C difference compared to 1°C difference Compare melting point difference of non-fluorinated to fluorinated: 11°C difference compared to 37°C difference Compound Boiling Point (°C) Melting Point C3H7I (1-iodo) 102 -101 (2-iodo) 90 -90 C3F7I 41 -95 40 -58

Boiling and melting points Compare boiling point difference of non-fluorinated to fluorinated: 12°C difference compared to 1°C difference Compare melting point difference of non-fluorinated to fluorinated: 11°C difference compared to 37°C difference Compound Boiling Point (°C) Melting Point C3H7I (1-iodo) 102 -101 (2-iodo) 90 -90 C3F7I 41 -95 40 -58

Boiling and melting points Compare boiling point difference of non-fluorinated to fluorinated: 12°C difference compared to 1°C difference Compare melting point difference of non-fluorinated to fluorinated: 11°C difference compared to 37°C difference Compound Boiling Point (°C) Melting Point C3H7I (1-iodo) 102 -101 (2-iodo) 90 -90 C3F7I 41 -95 40 -58

Boiling and melting points Compare boiling point difference of non-fluorinated to fluorinated: 12°C difference compared to 1°C difference Compare melting point difference of non-fluorinated to fluorinated: 11°C difference compared to 37°C difference Compound Boiling Point (°C) Melting Point C3H7I (1-iodo) 102 -101 (2-iodo) 90 -90 C3F7I 41 -95 40 -58

Infrared Spectroscopy C-αF stretch

Infrared Spectroscopy

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

NMR Less shielding More shielding

NMR Less shielding More shielding

NMR Less shielding Halogen bonding More shielding

Less shielding Halogen bonding More shielding

Less shielding Halogen bonding More shielding

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

Concordia Chemistry Research Fund Acknowledgements Dr. Haiyan Fan Dr. Mark Gealy Jeff Eliason Scott Flancher Diane Moliva Danny Green NSF CAREER: CHE-0341087 Dreyfus Foundation Concordia Chemistry Research Fund

Importance of the a Fluorine

Infrared Spectroscopy