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

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


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


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 ?

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

NMR

•19F-NMR•α-peak and β-peak behavior•Measures amount

of electron shielding

NMRMore shieldingLess shielding

NMRMore 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

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

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Transcript of Homo-halogen Bonding in 2-iodo-perfluoroalkane Darin J. Ulness Department of Chemistry Concordia...