Galen Sedo Kenneth Leopold Group University of Minnesota A Microwave and ab initio Study of (CH 3 ) 3 CCN--SO 3

The SO 3 -NX Lewis Acid-Base Series † † S. W. Hunt, and K. R. Leopold, J. Phys. Chem. A 2001, 105, van der Waals Chemically Bound 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

The SO 3 -NX Lewis Acid-Base Series † † S. W. Hunt, and K. R. Leopold, J. Phys. Chem. A 2001, 105, van der Waals Chemically Bound Sum of N & S van der Waals radii N-S Covalent Bond

Sum of N & S van der Waals radii N-S Covalent Bond The SO 3 -NX Lewis Acid-Base Series † † S. W. Hunt, and K. R. Leopold, J. Phys. Chem. A 2001, 105, van der Waals Chemically Bound

The SO 3 -NX Lewis Acid-Base Series † van der Waals Chemically Bound Tert-butyl cyanide’s lone pair has a proton affinity of kcal/mol A simple fit of the Lewis base proton affinity vs. physical property predicts: R(N-S) = 2.31 ET = 0.21e -

The SO 3 -NX Lewis Acid-Base Series † van der Waals Chemically Bound † L. J. Nugent, D. E. Mann, and D. R. Lide, J. Chem. Phys. 1961, 36(4),

Pulse Line with Polymerized SO 3 Series 9 Pulsed Solenoid Valve Needle Adaptor Glass Bubble With Liquid Tert-butyl Cyanide Pulsed Nozzle FTMW Experimental Setup 1.Pulse Line 18 psig Argon Carrier Gas passed over Polymerized SO 3. 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

(CH 3 ) 3 CCN projection: |m| = 0, 1, 2 SO 3 projection: |K-m| = 0, 3 84 line over three transitions J = 3 → 4 J = 4 → 5 J = 5 → 6 † G. T. Fraser, F. J. Lovas, R. D. Suenram, D. D. Nelson, and W. Klemperer J. Chem. Phys. 1986, 84(11),

Nitrogen – Sulfur Dative Bond Length

(CH 3 ) 3 CCN Excursion Angle (  ): Assume similar bending force constants for the “intermediate” complexes Monomer Excursion & Distortion Angles SO 3 Excursion Angle (  ): Estimated to be between zero and the value in weakly bound Ar-SO 3 (15.6 o ) SO 3 Distortion Angle (  ): Estimated to be the MP2/aug-cc-pvtz angle (2.8 o ) ± 50% (1.4 o ) [HCN-SO 3 (1.8 o )] [HCCCN-SO 3 (1.7 o )] [CH 3 CN-SO 3 (2.0 o )]

Nitrogen – Sulfur Dative Bond Length

Sum of N & S van der Waals radii N-S Covalent Bond Nitrogen – Sulfur Dative Bond Length

N 2 -SO 3 R NS = 2.937(4) Å (CH 3 ) 3 CCN-SO 3 R NS = 2.375(35) Å (CH 3 ) 3 N-SO 3 R NS = 1.912(20) Å } } Å (~55%) Å (~45%) Sum of N & S van der Waals radii N-S Covalent Bond

Electron Transfer a Townes and Dailey analysis † a s 2 → s character of hybrid orbital   → electron population on Nitrogen atom eqQ N → eqQ of atomic Nitrogen 2p z electron † Townes, C. H.; Dailey, B. P. J. Chem. Phys. 1949, 17, 782.

Electron Transfer a Townes and Dailey analysis † N 2 -SO 3 ET = 0.04 e - (CH 3 ) 3 CCN-SO 3 ET = 0.18 e - (CH 3 ) 3 N-SO 3 ET = 0.57 e - } } 0.14 e - (~26%) 0.39 e - (~74%)

MP2/aug-cc-pvtz (CH 3 ) 3 CCN-SO 3 ab initio Calculations N 2 -SO 3 E binding = 3.24 kcal/mol (CH 3 ) 3 CCN-SO 3 E binding = kcal/mol (CH 3 ) 3 N-SO 3 E binding = kca/mol } } 7.77 kcal/mol (~21%) kcal/mol (~79%)

Conclusions 1.The (CH 3 ) 3 CCN-SO 3 spectrum was found using the N-S bond Length predicted from the SO 3 -NX series. 2.The (CH 3 ) 3 CCN-SO 3 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. R NS = 2.375(35) Å ET = 0.18 e - E binding = kcal/mol 3.The (CH 3 ) 3 CCN-SO 3 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  = 1.4  = 0  = 15.6  = 0  = 6.75  = 4.2 R NS = 2.386(40) R NS = 2.375(35)