Galen Sedo Kenneth Leopold Group University of Minnesota [email protected] A Microwave and ab initio...

Galen Sedo

Kenneth Leopold GroupUniversity of Minnesota

[email protected]

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




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


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


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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


Ele

ctro

n T

rans

fer [

e- ]

12 3 4

5

67


1.50

2.00

2.50

3.00

110.0 130.0 150.0 170.0 190.0 210.0 230.0


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




1

3

2

7

6

4 5



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



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)]


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


1.500

2.000

2.500

3.000

110.0 130.0 150.0 170.0 190.0 210.0 230.0


N-S

Bon

d L

engt

h [Å

] Sum of N & S van der Waals radii

N-S Covalent Bond


Å35375.2

sincos1sincos1 2)(212)(

212

212

212 333333

NS

Scm

NcmCMNS

CCNCHcc

CCNCHbb

SOcc

SObbcms

complexbb

R

RRRR

IIIIRMI


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%)


1.500

2.000

2.500

3.000

110.0 130.0 150.0 170.0 190.0 210.0 230.0


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.


0.00

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110.0 130.0 150.0 170.0 190.0 210.0 230.0


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†


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0.30

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0.50

0.60

0.70

110.0 130.0 150.0 170.0 190.0 210.0 230.0


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


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)

http://www.umn.edu/

http://www.nsf.gov/home/news.html

= 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

Galen Sedo Kenneth Leopold Group University of Minnesota [email protected] A Microwave and ab initio...

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Transcript of Galen Sedo Kenneth Leopold Group University of Minnesota [email protected] A Microwave and ab initio...