Homo-halogen Bonding in 2-iodo-perfluoroalkane
Darin J. UlnessDepartment 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
Halogen Bonding
Biochemistry• Biomolecular engineering• Drug Design
Materials Science• Crystal engineering• Molecular recognition
ComputationalChemistry
• s hole bondingVoth A. R. et.al. PNAS 2007;104:6188-6193 Resnati et.al. J. Fluorine Chem.
2004;104: 271
The s hole
I
Test ChargeFree Iodine
Atom
Test Charge “feels” an electroneutral field
Test charge far from an iodine atom
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
Test Charge
In molecules the electron density is directed into the bond
The s hole
Electropositves-hole
Test Charge
Electroneutral“ring”
Electronegative“belt”
The s hole
Electropositves-hole
Test Charge
Electroneutral“ring”
Electronegative“belt”
Perfluorinate: Stronger s hole
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
C C
C
C
N
C
C C
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
C C
C
free pyridine
C
N
C
C C
C
O
HH
H-bonded pyridine
I(2)CARS Experiment
Monochromator
NarrowbandSource
BroadbandSource(noisy light)
Lens
Sample
Interferometer
t
B
B’
MI(2)CARS
ComputerCCD
Pyridine as a probe
980 1000 1020 1040
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d X
-ma
rgin
al
Wavenumber / cm-1
Pyridine as a probe
980 1000 1020 1040
0.0
0.2
0.4
0.6
0.8
1.0 100% pyr 85% pyr 70% pyr 55% pyr 25% pyr
No
rma
lize
d X
-ma
rgin
al
Wavenumber / cm-1
freepyridine
H-bondedpyridine
ring-breathing
Pyridine as a probe of Halogen bonding
C4F9I
C6F13IC3F7I
2-iodo-perfluoropropane
1-iodo-perfluoroalkanes
1-iodo-perfluoroalkanes
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Neat
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
C6F13I and Pyridine
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100Frequency (cm-1)
Norma
lized In
tesity
Neat
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
C4F9I C6F13I
2-iodo-perfluoropropane
C6F13I and Pyridine
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100Frequency (cm-1)
Norma
lized In
tesity
Neat
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
C3F7I C6F13I
Pyridine and C3F7I
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Neat
Temperature StudiesC3F7I C6F13I
C3F7I Temp Study
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
c3f7ipy65Cc3f7ipy50Cc3f7ipy35Cc3f7ipy25Cc3f7ipy15Cc3f7ipy0Cc3f7ipy -15Cc3f7ipy -30C0.9
Neat Py25C
Name
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
c6f13ipy60Cc6f13ipy40Cc6f13ipy25Cc6f13ipy15Cc6f13ipy0Cc6f13ipy-15Cc6f13ipy-25C0.8
0.9
Neat
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 (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
F C I
C
CF
F
F
F
F
F hF C
C
CF
F
F
F
F
F
+ I
F C
C
CF
F
F
F
F
F
C F
C
CF
F
F
F
F
F
+ I I
x2
Time 20min Time 30min Time 45min
Time 60min Time 90min Time 18hrs
X=0.2Neat X=0.2Neat X=0.2Neat
X=0.2Neat X=0.2Neat X=0.2Neat
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
C3H7I (2-iodo)
90 -90
C3F7I (1-iodo)
41 -95
C3F7I (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
Compound Boiling Point (°C)
Melting Point
C3H7I (1-iodo)
102 -101
C3H7I (2-iodo)
90 -90
C3F7I (1-iodo)
41 -95
C3F7I (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
Compound Boiling Point (°C)
Melting Point
C3H7I (1-iodo)
102 -101
C3H7I (2-iodo)
90 -90
C3F7I (1-iodo)
41 -95
C3F7I (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
Compound Boiling Point (°C)
Melting Point
C3H7I (1-iodo)
102 -101
C3H7I (2-iodo)
90 -90
C3F7I (1-iodo)
41 -95
C3F7I (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
Compound Boiling Point (°C)
Melting Point
C3H7I (1-iodo)
102 -101
C3H7I (2-iodo)
90 -90
C3F7I (1-iodo)
41 -95
C3F7I (2-iodo)
40 -58
NMR
•19F-NMR•α-peak and β-peak behavior•Measures amount
of electron shielding
NMRMore shieldingLess shielding
NMRMore shieldingLess shielding
NMRMore shieldingLess shielding Halogen bonding
More shieldingLess shielding Halogen bonding
More shieldingLess shielding Halogen bonding
Conclusion
Homo-halogen bonding
Boiling and melting points
KineticsIodine production
ratesGeminate pair
recombination
NMRShift in α-peakShielding levels based
on temperature
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
Pyridine and H2H
0
0.5
1
1.5
2
2.5
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Neat
Infrared Spectroscopy
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