Homo-halogen Bonding in 2-iodo-perfluoroalkane

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

2. Hydrogen bonding • History • The s hole and s hole bonding • Data • Discussion Outline

3. 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 Hydrogen Bonding

4. 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

5. 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: History

6. Biochemistry • Biomolecular engineering • Drug Design • Materials Science • Crystal engineering • Molecular recognition Halogen Bonding: Today 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

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

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

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

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

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

12. s hole bonding with pyridine

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

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

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

16. Pyridine as a probe

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

18. 1-iodo-perfluoroalkanes Pyridine as a probe of Halogen bonding 2-iodo-perfluoropropane C3F7I C6F13I C4F9I

19. C4F9I C6F13I 1-iodo-perfluoroalkanes

20. C3F7I C6F13I 2-iodo-perfluoropropane

21. C3F7I C6F13I Temperature Studies

22. 2-iodo-perfluoropropane 1-iodo-perfluoroalkanes I’m Special !

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

24. One is better than two ?

25. One is better than two ?

26. To test the homo-halogen bonding hypothesis utilized several techniques • Analysis of physical properties • 19F-NMR • IR (data not discussed) • Noticed photochemical dissociation when left in room lights • Suggested a kinetics study Strategies

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

28. Time 20min Time 30min Time 45min 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

29. 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 Kinetics

30. 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 Boiling and melting points

31. 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 Boiling and melting points

32. 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 Boiling and melting points

33. 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 Boiling and melting points

34. 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 Boiling and melting points

35. 19F-NMR • α-peak and β-peak behavior • Measures amount • of electron shielding NMR

36. More shielding Less shielding NMR

37. More shielding Less shielding NMR

38. Halogen bonding More shielding Less shielding NMR

39. Halogen bonding More shielding Less shielding

40. Halogen bonding More shielding Less shielding

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

42. 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

44. Importance of the a Fluorine

45. Infrared Spectroscopy