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Galen Sedo
Kenneth Leopold GroupUniversity of Minnesota
A Microwave and ab initio Study of (CH3)3CCN--SO3
The SO3-NX Lewis Acid-Base Series†
† S. W. Hunt, and K. R. Leopold, J. Phys. Chem. A 2001, 105, 5498-5506.
van der WaalsChemically Bound
1
3
2
7
6
4 5
A series of seven Lewis Acid-Base complexes have previously been observed.
The strength of the Acid-Base interaction was observed to progress through the series.
• N-S Bond Length
• Electron Transfer away from the Nitrogen atom
The strength of the Acid-Base interaction through the series is related to the gas phase basicity.
• Nitrogen’s Lone Pair Proton Affinity
Proton Affinity vs. Electron Transfer
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
Ele
ctro
n T
rans
fer [
e- ]
12 3 4
5
67
The SO3-NX Lewis Acid-Base Series†
† S. W. Hunt, and K. R. Leopold, J. Phys. Chem. A 2001, 105, 5498-5506.
van der WaalsChemically Bound
1
3
2
7
6
4 5
Proton Affinity vs. N-S Bond Length
1.50
2.00
2.50
3.00
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
N-S
Bon
d L
engt
h [Å
]
3
1
2
765
4
Sum of N & S van der Waals radii
N-S Covalent Bond
Proton Affinity vs. Electron Transfer
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
Ele
ctro
n T
rans
fer [
e- ]
12 3 4
5
67
Proton Affinity vs. N-S Bond Length
1.50
2.00
2.50
3.00
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
N-S
Bon
d L
engt
h [Å
]
3
1
2
765
4
Sum of N & S van der Waals radii
N-S Covalent Bond
The SO3-NX Lewis Acid-Base Series†
† S. W. Hunt, and K. R. Leopold, J. Phys. Chem. A 2001, 105, 5498-5506.
van der WaalsChemically Bound
1
3
2
7
6
4 5
The SO3-NX Lewis Acid-Base Series†
van der WaalsChemically Bound
1
3
2
7
6
4 5
• Tert-butyl cyanide’s lone pair has a proton affinity of 193.8 kcal/mol
• A simple fit of the Lewis base proton affinity vs. physical property predicts:
R(N-S) = 2.31 ET = 0.21e-
N
H3C
H3CH3C
S
O
OO
MHz
IIRMI
RRRR
J
CCNCHbb
SObbCMs
complexbb
Scm
NcmNSCM
373543
)(2
†
333
The SO3-NX Lewis Acid-Base Series†
van der WaalsChemically Bound
1
3
2
7
6
4 5
N
H3C
H3CH3C
S
O
OO
NcmR NSR
CMR
†L. J. Nugent, D. E. Mann, and D. R. Lide, J. Chem. Phys. 1961, 36(4), 965-971.
Pulse Line withPolymerized SO3
Series 9PulsedSolenoidValve
Needle Adaptor
Glass BubbleWith Liquid
Tert-butyl Cyanide
Pulsed Nozzle FTMWExperimental Setup
1. Pulse Line• 18 psig Argon Carrier Gas passed
over Polymerized SO3.
2. Continuous Flow Needle Injection• Single Stainless Steel Needle
Outer Diameter = 0.028"
Inner Diameter = 0.016"
Length = 0.205"
• Mass Flow Regulator prior to a Glass Bubble containing Liquid Tert-butyl Cyanide
Flow Rate = 2.5 sccm Argon
Line Assignments and Fitting
J = 3 → 4
3578.750 3578.950 3579.150 3579.350 3579.550 3579.750 3579.950 3580.150
Frequency [MHz]
Line Assignments and Fitting
†
3
2222
14
12
quadJ
JKmJKmJmJK
EDJ
KmHKmDmDKDBJ
(CH3)3CCN projection: |m| = 0, 1, 2
SO3 projection: |K-m| = 0, 3
84 line over three transitions J = 3 → 4J = 4 → 5J = 5 → 6
|K| |m| m K F" F' F obs
a calc
a obs-calc
a
0 0 0 4 4 0 3578.859 3578.868 -0.0092 3 1 3579.910 3579.917 -0.0073 4 1 3579.983 3579.989 -0.0064 5 1 3580.015 3580.015 0.0003 3 0 3581.421 3581.430 -0.009
1 2 -2 3 4 1 3579.161 3579.163 -0.0022 3 1 3579.250 3579.253 -0.0034 5 1 3579.293 3579.297 -0.004
1 1 1 4 4 0 3579.040 3579.034 0.0063 4 1 3579.879 3579.875 0.0042 3 1 3579.969 3579.965 0.0044 5 1 3580.005 3580.008 -0.0033 3 0 3581.106 3581.099 0.007
2 1 -2 3 4 1 3579.101 3579.097 0.0044 4 0 3579.101 3579.097 0.0044 5 1 3579.557 3579.556 0.0012 3 1 3579.680 3579.674 0.0063 3 0 3579.680 3579.674 0.006
2 2 4 3 4 1 3579.583 3579.583 0.0004 4 0 3579.583 3579.583 0.0004 5 1 3580.041 3580.041 0.0002 3 1 3580.160 3580.159 0.0013 3 0 3580.160 3580.159 0.001
3 0 0 3 4 1 3578.776 3578.776 0.0004 5 1 3579.772 3579.776 -0.0042 3 1 3580.160 3580.163 -0.003
(CH3)3CCN-SO3 Line Assignments for J = 3 → 4
a Values are in MHz
B 447.50018(25)
DJ 0.0000481(41)DJK 0.006338(19)
DJm 0.014098(48)
DJKm -0.016078(37)
HJKm -0.0005417(89)
eqQ -3.3626(39)b All values are in MHz
(CH3)3CCN-SO3 Constantsb
B 447.50018(25)
DJ 0.0000481(41)DJK 0.006338(19)
DJm 0.014098(48)
DJKm -0.016078(37)
HJKm -0.0005417(89)
eqQ -3.3626(39)b All values are in MHz
(CH3)3CCN-SO3 Constantsb
† G. T. Fraser, F. J. Lovas, R. D. Suenram, D. D. Nelson, and W. Klemperer J. Chem. Phys. 1986, 84(11), 5983-5988.
J = 3 → 4
3578.750 3578.950 3579.150 3579.350 3579.550 3579.750 3579.950 3580.150
Frequency [MHz]
2)(212)(
212
212
212 sincos1sincos1 333333 CCNCH
ccCCNCH
bbSOcc
SObbcms
complexbb IIIIRMI
Å430.2
333 )(2
NS
Scm
NcmCMNS
CCNCHbb
SObbCMs
complexbb
R
RRRR
IIRMI
N
CH3
H3C
H3CS
O
O
O90 +
C3 axis
MolecularAxis
C3 axis
N
H3C
H3CH3C
S
O
OONSRN
cmR
CMR
Nitrogen – Sulfur Dative Bond Length
(CH3)3CCN Excursion Angle (): Assume similar bending force constants for the “intermediate” complexes
4
1)(
)(33
33
basebb
CCNCHbb
base
CCNCH
I
I
[deg] max [deg]
HCN-SO3 8.3 ± 4.6 11.108 4.1 6.4
HCCCN-SO3 4.7 ± 2.6 111.095 4.1 6.4CH3CN-SO3 6 ± 3 54.939 4.4 6.7
4.2 6.5
(CH3)3CCN Excursion Angle ()
Complex(CH3)3CCN-SO3 [deg] Ibb
base [MHz]
Average
Monomer Excursion & Distortion Angles
N
CH3
H3C
H3CS
O
O
O90 +
C3 axis
MolecularAxis
C3 axis
SO3 Excursion Angle (): Estimated to be between zero and the value in weakly bound Ar-SO3 (15.6o)
SO3 Distortion Angle (): Estimated to be the MP2/aug-cc-pvtz angle (2.8o) ± 50% (1.4o)[HCN-SO3 (1.8o)] [HCCCN-SO3 (1.7o)] [CH3CN-SO3 (2.0o)]
Nitrogen – Sulfur Dative Bond Length
N
CH3
H3C
H3CO
OO
MolecularAxis S
ScmNS RR
NcmR
CMR
Å35375.2
sincos1sincos1 2)(212)(
212
212
212 333333
NS
Scm
NcmCMNS
CCNCHcc
CCNCHbb
SOcc
SObbcms
complexbb
R
RRRR
IIIIRMI
Proton Affinity vs. N-S Bond Length
1.500
2.000
2.500
3.000
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
N-S
Bon
d L
engt
h [Å
] Sum of N & S van der Waals radii
N-S Covalent Bond
Nitrogen – Sulfur Dative Bond Length
Å35375.2
sincos1sincos1 2)(212)(
212
212
212 333333
NS
Scm
NcmCMNS
CCNCHcc
CCNCHbb
SOcc
SObbcms
complexbb
R
RRRR
IIIIRMI
Nitrogen – Sulfur Dative Bond Length
N2-SO3 RNS= 2.937(4) Å
(CH3)3CCN-SO3 RNS= 2.375(35) Å
(CH3)3N-SO3 RNS= 1.912(20) Å
}}
0.559 Å (~55%)
0.463 Å (~45%)
Proton Affinity vs. N-S Bond Length
1.500
2.000
2.500
3.000
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
N-S
Bon
d L
engt
h [Å
] Sum of N & S van der Waals radii
N-S Covalent Bond
Electron Transfera Townes and Dailey analysis†
NsCCNCHcomplex eqQaeqQeqQ 12 22)( 33
as2 → s character of hybrid orbital
→ electron population on Nitrogen atom
eqQN → eqQ of atomic Nitrogen 2pz electron
† Townes, C. H.; Dailey, B. P. J. Chem. Phys. 1949, 17, 782.
Proton Affinity vs. Electron Transfer
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
Ele
ctro
n T
rans
fer [
e- ]
eqQ complex [MHz]
eqQ C5H9N [MHz]eqQ Complexation [MHz]
ET [e-]
-4.213
0.851
0.19
(CH3)3CCN-SO3 Quadrupole Coupling & Electron Transfer
-3.363eqQ complex [MHz]
eqQ C5H9N [MHz]eqQ Complexation [MHz]
ET [e-]
‹P2 (cos )› 0.992a 0.981b
eqQ zpccomplex [MHz] -3.390a -3.434b
ET Zero-Point Corrected [e-] 0.18a 0.17b
-4.213
0.851
0.19
(CH3)3CCN-SO3 Quadrupole Coupling & Electron Transfer
-3.363
a = 4.2o b = 6.5o
Electron Transfera Townes and Dailey analysis†
Proton Affinity vs. Electron Transfer
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
Ele
ctro
n T
rans
fer [
e- ]N2-SO3 ET = 0.04 e-
(CH3)3CCN-SO3 ET = 0.18 e-
(CH3)3N-SO3 ET = 0.57 e-
}}
0.14 e- (~26%)
0.39 e- (~74%)
MP2/aug-cc-pvtz
(CH3)3CCN-SO3 ab initio Calculations
RNS [Å] 2.40
SO3 Distortion () [deg] 2.79
Ebinding [kcal/mol] 11.01E
distortion [kcal/mol] -1.01
Calculated MP2/aug-cc-pvtz Values
Proton Affinity vs. Binding Energy
05
1015202530354045
110.0 130.0 150.0 170.0 190.0 210.0 230.0
Proton Affinity [kcal/mol]
Bin
ding
Ene
rgy
[kca
l/m
ol]
N2-SO3 Ebinding = 3.24 kcal/mol
(CH3)3CCN-SO3 Ebinding = 11.01 kcal/mol
(CH3)3N-SO3 Ebinding = 40.04 kca/mol
}}
7.77 kcal/mol (~21%)29.03 kcal/mol (~79%)
Conclusions
1. The (CH3)3CCN-SO3 spectrum was found using the N-S bond Length predicted from the SO3-NX series.
2. The (CH3)3CCN-SO3 N-S bond Length and degree of electron transfer were calculated from the fit spectroscopic constants, and the theoretical binding energy of the complex was calculated.
RNS= 2.375(35) Å ET = 0.18 e- Ebinding= 11.01 kcal/mol
3. The (CH3)3CCN-SO3 complex shows an interaction strength intermediate to the van der Waals and chemically bound limits.
~55% ~26% ~21%
• Dr. Kenneth Leopold
• Carolyn Brauer
• Erik Grumstrup
Acknowledgements
Funding
• National Science Foundation (NSF)
• Petroleum Research Fund (PRF)
• Minnesota Supercomputing Institute (MSI)
= 0, 3, 6, 9, 12, 15.6
= 0, 1.125, 2.25, 3.375, 4.5, 5.625, 6.75
= 1.4, 2.8, 4.2
Law of Cosines
2.350
2.360
2.3702.380
2.390
2.400
2.4102.420
2.430
2.440
0 20 40 60 80 100 120 140
RN
S [Å
]
Vibrationally Averaged
2.330
2.3402.350
2.3602.370
2.3802.390
2.4002.410
2.420
0 20 40 60 80 100 120 140
RN
S [Å
]
= 1.4
= 0
= 15.6
=
0
=
6.75
= 4.2
RNS= 2.386(40)
Scm
NcmCM
NcmCMNS RRRRRR 2
1
cos222
RNS= 2.375(35)
Scm
NcmCMNS RRRR