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

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

3. 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

4. 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

5. 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

6. 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:
Resnati et.al. J. Fluorine Chem.
2004;104: 271

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

8. 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 !

9. 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

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

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

12. s hole bonding with pyridine

13. 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

14. 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

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

16. Pyridine as a probe

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

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

19. 1-iodo-perfluoroalkanes
C4F9I
C6F13I

20. 2-iodo-perfluoropropane
C3F7I
C6F13I

21. Temperature Studies
C3F7I
C6F13I

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

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

24. One is better than two ?

25. One is better than two ?

26. 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

27. 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

28. 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

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

30. 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

31. 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

32. 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

33. 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

34. 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

35. Infrared Spectroscopy
C-αF stretch

36. Infrared Spectroscopy

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

38. NMR
Less shielding
More shielding

39. NMR
Less shielding
More shielding

40. NMR
Less shielding
Halogen bonding
More shielding

41. Less shielding
Halogen bonding
More shielding

42. Less shielding
Halogen bonding
More shielding

43. 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

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

46. Importance of the a Fluorine

47. Infrared Spectroscopy