proton sponges: a rigid organic scaffold to reveal the quantum structure of the intramolecular...
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Proton Sponges: A Rigid Organic Scaffold to Reveal the Quantum Structure of the
Intramolecular Proton Bond
Andrew F. DeBlase, Michael T. Scerba, Thomas Lectka, and Mark A. Johnson
June 22, 2012
A BH
1 8
Background• Tom Lectka (organic): Isolate exotic charged H-bonds
N FH3C
H3C H
Scerba et. al. J. Org. Chem. 2011
- e.g. Charged H-bond to F
• Our work: Shared proton often a distinct feature in cold ions
Roscioli et. al. Science 2007Ar-predissociation of cryogenic ions
1000 1500 2000 2500 3000 3500 Photon Energy (cm-1)
O H+
OCH2CH3
CH2CH3
CH3CH2
CH3CH2
Stoyanov and Reed J. Phys. Chem. A 2006Room temperature FTIR
Background• Tom Lectka (organic): Isolate exotic charged H-bonds
N FH3C
H3C H
Scerba et. al. J. Org. Chem. 2011
- e.g. Charged H-bond to F
• Our work: Shared proton often a distinct feature in cold ions
“I think this is the beginning of a beautiful friendship.”
Background• Tom Lectka (organic): Isolate exotic charged H-bonds
N FH3C
H3C H
Scerba et. al. J. Org. Chem. 2011
- e.g. Charged H-bond to F
• Our work: Shared proton often a distinct feature in cold ions
“I think this is the beginning of a beautiful friendship.”
• Can you make an H-bond to the ether oxygen of an ester?
N OH3CH3C
HO
Why Is This Unusual?
COR1
O
R2
H
COR1
O
R2
HThe carbonyl O has a much higher proton affinity!
Why Is This Unusual?
COR1
O
R2
H
COR1
O
R2
H
COR1
O
R2
H
COR1
O
R2
H
R1 C O HOR2+
The carbonyl O has a much higher proton affinity!
Very Fast
Bohme Int. J. Mass Spectrom. 2000
N OH3CH3C
HO
Blue shift?COR1
O
R2
R1 C OCOR1
O
R2
H
νCO
Experimental Setup
Ion optics
ElectrosprayNeedle
RF Only Quadrupoles
Octopoles
Pressure (Torr)
3D Quadrupole Ion Trap with Temperature Control to 8 K
TOF to IR Spectrometer
New Cryogenic Ion Source
3×10-7 1×10-5 1.5×10-2 1.5 760
HeatedCapillary
90° Ion Bender
Wiley-McLarenExtraction Region
N OH3CH3C
HO
N OH3CH3C
DO
+ D2
+ D2
13C
290 292 294 296 298 300
m/z
The Experiment
*
+ D2
13C
290 292 294 296 298 300
m/z
N OH3CH3C
DO
The Experiment
hν
OPO/OPA LaserVisionMid Infrared Laser
Apply mass gate to ion of interest
+ D2
13C
N OH3CH3C
DO
Time of Flight
Monitor photofragmentas a function of laser energy
The Experiment
N OH3CH3C
HO
O O
H
Photon Energy (cm-1)
νNH
1000 1200 1400 1600 1800 2800 3000 3200 3400
H3C CH3
OH
Pre
dis
soci
atio
n Y
ield
, C
alc
ula
ted
In
ten
sity
Blue Shifted Carbonyl: Evidence for a Strong Intramolecular H-Bond
Scerba et. al. J. Phys. Chem. A. 2012.
νCO
33781580
O O
1720
νOH= 3313νCO= 1500-1700
1792
B3LYP/6-311++G**(unscaled)
B3LYP/6-311++G**(CH scaled by 0.961,NH scaled by 0.945)
Douberly, et. al. PCCP 2008
Course, et. al. JOC 1981
Wow!!!
N OH3CH3C
HO
Photon Energy (cm-1)
νNH
1000 1200 1400 1600 1800 2800 3000 3200 3400
Pre
dis
soci
atio
n Y
ield
, C
alc
ula
ted
In
ten
sity
Blue Shifted Carbonyl: Evidence for a Strong Intramolecular H-Bond
Scerba et. al. J. Phys. Chem. A. 2012.
νCO
1792
B3LYP/6-311++G**(unscaled)
B3LYP/6-311++G**(CH scaled by 0.961,NH scaled by 0.945)
N OH3C
H3CH
O
+ N OH3C
H3CH
O
++
Is the complexity from the reaction coordinate?
N OH3C
H3CH
O
Ph
Pre
dis
soci
atio
n Y
ield
, C
alc
ula
ted
In
ten
sity
Photon Energy (cm-1)2800 3000 3200 3400 3600 3800
Calculated:B3LYP/6-311++G**Scaled by 0.966
Tuning the Shared Proton Frequency2750-3200
· D2
N OH3C
H3C H H
3614
3637
· D2
Pre
dis
soci
atio
n Y
ield
, C
alc
ula
ted
In
ten
sity
N OH3C
H3CH H
N OH3C
H3CH H
D
D
Photon Energy (cm-1)1500 2000 2500 3000 3500
Calculated:MP2/6-311++G**Scaled: OH = 0.945,CH/NH = 0.957, below 2000 cm-1 = 0.972
Alcohol Isotopologues
2750-3200
3614
3637
N OH3C
H3CD H
Case 1:
ND OH
N OH3C
H3CH D
Case 2:
NHOD
Photon Energy (cm-1)
Pre
dis
soci
atio
n Y
ield
, C
alc
ula
ted
In
ten
sity
N OH3C
H3CH H
N OH3C
H3CH H
D
D
N OH3C
H3CD H
N OH3C
H3CD D
1500 2000 2500 3000 3500
Calculated:MP2/6-311++G**Scaled: OH = 0.945,CH/NH = 0.957, below 2000 cm-1 = 0.972
Alcohol Isotopologues
2750-3200
2264
2268
3614
2672
3637
2687
Photon Energy (cm-1)
Pre
dis
soci
atio
n Y
ield
, C
alc
ula
ted
In
ten
sity
N OH3C
H3CH H
N OH3C
H3CH H
D
D
N OH3C
H3CD H
N OH3C
H3CD D
~ X 4 Laser Power
1500 2000 2500 3000 3500
Alcohol Isotopologues
N OH3C
H3CH
O
Ph
1200 1600 2000 2400 2800 3200
Photon Energy (cm-1)
Pre
diss
ocia
tion
Yie
ld,
Cal
cula
ted
Inte
nsity
N OH3C
H3CD
O
Ph
Ester Isotopologues
Woof, woof!!
2267
2750-2960
2960-3200
1793
1795
Conclusions/Future Work
• Revealed signature carbonyl of Oether H-bond interaction
• NH stretching region complicated through couplings to other oscillators and possibly dark states
- Can we tune through these by making Δ PA even smaller?
• Can the shared proton launch a chemical reaction?
NH3C
H3C H SiPh3O
Acknowledgements• Labmates: Past and Current• Mark: New science, new hobbies!• Tom Lectka’s group at JHU for making the molecules!• Ken Jordan for help with calculations• Anne McCoy for useful conversations about
anharmonicity• Funding: National Science Foundation, Air Force
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