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

Outline Hydrogen bonding History The  hole and  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 180 o

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

Halogen Bonding: History F. Guthrie, J. Chem. Soc. 16, 239 (1863) Complexation of I 2 and NH 3 I. Remsen, J.F. Norris, Am. Chem. J. 18, 90, (1896) Complexation of X 2 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 Halogen Bonding Biochemistry Biomolecular engineering Drug Design Materials Science Crystal engineering Molecular recognition Computational Chemistry  hole bonding Voth A. R. et.al. PNAS 2007;104: Resnati et.al. J. Fluorine Chem. 2004;104: 271

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

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

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

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

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

 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 CC C C N C CC C “ring-breathing” mode “triangle” mode

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

I (2) CARS Experiment Monochromator Narrowband Source Broadband Source (noisy light) Lens Sample Interferometer  B B’ M I (2) CARS Computer CCD

Pyridine as a probe

free pyridine H-bonded pyridine ring-breathing

Pyridine as a probe of Halogen bonding C4F9IC4F9I C 6 F 13 I C3F7IC3F7I 2-iodo-perfluoropropane 1-iodo-perfluoroalkanes

C4F9IC4F9IC 6 F 13 I

2-iodo-perfluoropropane C3F7IC3F7IC 6 F 13 I

Temperature Studies C3F7IC3F7IC 6 F 13 I

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

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

One is better than two ?

Strategies To test the homo-halogen bonding hypothesis utilized several techniques Analysis of physical properties 19 F-NMR IR (data not discussed) 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 20minTime 30minTime 45min Time 60minTime 90minTime 18hrs X=0.2NeatX=0.2NeatX=0.2Neat X=0.2NeatX=0.2Neat X=0.2Neat

Kinetics Different rate constants observed k obs = min -1 in hexane (after correction for mole fraction) k obs = min -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 CompoundBoiling Point (°C) Melting Point C 3 H 7 I (1-iodo) C 3 H 7 I (2-iodo) C 3 F 7 I (1-iodo) C 3 F 7 I (2-iodo) 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 CompoundBoiling Point (°C) Melting Point C 3 H 7 I (1-iodo) C 3 H 7 I (2-iodo) C 3 F 7 I (1-iodo) C 3 F 7 I (2-iodo) 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 CompoundBoiling Point (°C) Melting Point C 3 H 7 I (1-iodo) C 3 H 7 I (2-iodo) C 3 F 7 I (1-iodo) C 3 F 7 I (2-iodo) 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 CompoundBoiling Point (°C) Melting Point C 3 H 7 I (1-iodo) C 3 H 7 I (2-iodo) C 3 F 7 I (1-iodo) C 3 F 7 I (2-iodo) 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 CompoundBoiling Point (°C) Melting Point C 3 H 7 I (1-iodo) C 3 H 7 I (2-iodo) C 3 F 7 I (1-iodo) C 3 F 7 I (2-iodo) 40-58

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

NMR More shielding Less shielding

NMR More shielding Less shielding

NMR More shielding Less shielding Halogen bonding

More shielding Less shielding Halogen bonding

More shielding Less shielding Halogen bonding

Conclusion Homo-halogen bonding  Boiling and melting points  Kinetics  Iodine production rates  Geminate pair recombination  NMR  Shift in α-peak  Shielding levels based on temperature

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

Importance of the  Fluorine

Infrared Spectroscopy