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Research

Summary

My interests deal with solving mechanistic and structural problems in organic chemistry using modern quantum mechanical methodology. Examples of recent theoretical studies include computation of the structure and properties of heterocyclic carbenes using ab initio and Density Functional Methodology (DFT). We have computed thermochemical properties and magnetic resonance ring current effects to probe the aromaticity of cyclic carbenes that contain 6-pi electrons. There is evidence for significant aromatic stabilization if at least two nitrogen atoms are part of the pi system in the ring. When oxygen or sulfur is part of the cycle the stabilization is greatly reduced. Studies of bridging by halogens in 2-halo cations have revealed systematic dependency on halogen vs charge density.

Aromaticity

In a similar way, we are also looking at a wide variety of 6-membered ring systems in an attempt to systematize our understanding of the concept of "aromaticity." Since there is no universal measure of aromaticity several criteria have been examined including thermochemical comparisons (isodesmic comparisons) and magnetic resonance comparisons in an effort to find correlations between the diverse methods.

Tetrahedrene

Other major interests include computational studies of highly strained small molecules. We are trying to find the limits of strain in alkenes for example. One question we are addressing is how much a double bond can be strained and remain intact. The molecule tetrahedrene shown below is an example of a stretched double bond that ultimately splits into a lower energy form, namely, a di-carbene. This unique structure has a novel electronic orbital manifold that we are analyzing by molecular orbital methods. The highest energy molecular orbital shown below illustrates the carbenic nature of the molecule and the fact that the two centers are non-interacting. The next highest MO is by contrast highly delocalized. Our calculations indicate that tetrahedrene has the highest known degree of strain energy.

We are currently screening other systems for stable di-carbene and tri-carbene formation and are considering experimental approaches to these systems. In addition, other isomers of C₄H₂ are under investigation computationally. These include the highly strained small ring compounds: cyclobut-1-en-3-yne, bicyclo[1.1.0]buta-1,3-diene and cyclopropenylmethylene.

Collaborative Studies

Collaborative studies include computational studies of fragmentation reactions of oxychlorocarbenes, structures of halonium ions, the mechanism of alkyl azide/thioacetate reactions, properties and reactions of radical cations and properties of natural and un-natural base pairs. Lastly, we have been applying natural bond orbital methodology to analyze conformational preferences of various ions and molecules.

Another project involves computationoal analysis of †he structure and reactivity of ion pairs in the gas phase.

Awards & Honors

Goodman, L.; Sauers, R. R. “Diffuse Functions in Natural Bond Orbital Analysis”, J. Comp. Chem. 2006, 1, 1185-1192.

Zuev, P. S.; Sheridan, R. S.; Sauers, R. R.; Moss, R. A.; Chu, G. "Conformational Product Control in the Low-Temperature Photochemistry of Cyclopropylcarbenes," Org. Lett., 2006, 4963 - 4966.

Roth, H. D.; Herbertz, T.; Sauers, R. R.; Weng, H. "Intramoledcular Nucleophilic Capture of Radical Cations by Tethered Hydroxy Functions," Tetrahedron, 2006, 6471-6489.

Kolakowski, R. V.; Shangguan, N.; Wang, Z. Sauers, R. R.; Williams, L. J. "Mechanism of Thio Acid/Azide Amidation," J. Amer. Chem. Soc. 2006, 128, 5695-5702.

Moss, R. A.; Tian, J.; Sauers, R. R.; Sheridan, R. S.; Bhakta, A.; Zuev, P. S. "Kinetic Studies of the Cyclization of Singlet Vinylchlorocarbenes," Org. Letters 2005, 7, 4645-4648.

Goodman, L.; Sauers, R. R. "1-Fluoropropane. Torsional Potential Surface," J. Chem. Theory and Comp. 2005, 1185-1192.

Chu, G.; Moss, R. A.; Sauers, R. R. "Dichlorodiazirine: A Nitrogenous Precursor for Dichlorocarbene," J. Amer. Chem. Soc. 2005. 14206-14207.

Moss, R. A.; Fu, X.; Sauers, R. R.; Wipf, P. "Endo Entry to the Nortricyclyl-Norbornenyl Cation System: Stereochemistry in the Fragmentation of endo-5-Norbornenyl-2-oxychlorocarbene," J. Org. Chem. 2005, 70, 8554-8460.

Sauers, R. R.; Van Arnum, S. D. "1,4-Conjugate Additions of Methoxyamine and 1,1-Dimethylhydrazine to Hex-3-yne-2-one: A Facile Synthesis of Functionalized Isoxazole and Pyrazole Precursors," Syn. Comm. 2005, 35, 2003-2035.

Fu, X.; Moss, R. A.; Sauers, R. R.; Wipf, P. "The Fragmentation of exo-5-Norbornenyl-2-oxychlorocarbene: Stereochemistry and Mechanism," Tetrahedron Lett. 2005, 46, 4265-4268.

Chu, G.; Moss, R. A.; Sauers, R. R.; Sheridan, R. S.; Zuev, P. S. "Activation Energies for the 1,2-Carbon Migration of Ring-fused Cyclopropylchlorocarbenes," Org. Letters 2005, 7, 1371-1374.

Moss, R. A.: Chu, G.; Sauers, R. R. "Unprecidented Chemistry of an Aryloxychlorodiazirine: Generation of a Dihalodiazirine and Diazirinone," J. Amer. Chem. Soc. 2005, 127, 2408 - 2409.

Moss, R. A.; Fu, X.;Sauers, R. R. "The Fragmentation of 7-Norbornyloxychlorocarbene: SNi-like Transition States," Can. J. Chem. 2005,.

Liu, X.; Chu, G.; Moss, R. A.; Sauers, R. R.; Warmuth, R. "Fluorophenoxycarbene inside a hemicarcerand: A bottled singlet carbene," Angew. Chem. , 2005, 44, 1994-1997.

Moss, R. A.; Tian, J.; Sauers, R. R. “Solvent Equilibrated Ion Pairs from Chloroformate or Oxachlorocarbene Fragmentations,” Org. Lett. , 2004, 4293-4316.

Sauers, R. R.; Van Arnum, S. D. "Green Chemistry Analytical Method Development: A Revisit on the Use of Potassium Ferrioxalate as a Chemical Actinometer" Green Chem. 2004, 6, 578 - 582.

Goodman, L.; Sauers, R. R. "Ethyl Anion Preferred Conformation," Int. J. Quantum Chem. 2005, 102, 829-837.

Moss, R. A.; Zheng, F.; Fede, J-M.; Johnson, L. A.; Sauers, R. R. “Solvent Equilibrated Ion Pairs from Carbene Fragementation Reactions,” J. Amer. Chem. Soc. 2004, 126, 12421-12431.

Moss, R. A.; Sauers, R. R.; Sheridan, R. S.; Tian, J; and Zuev, P. S. “Ring Expansion of Noradamantylchlorocarbene: Visualization and Heavy Atom Tunneling” J. Amer. Chem. Soc. 2004, 126,10196-10197.

Moss, R. A.; Sauers, R. R.; Zheng, F.; Fu, X.; Bally, T.; Maltsev, A. “Rearrangements Concerted with Fragmentation of Cyclopropylmethoxychlorocarbene and Cyclobutoxychlorocarbene”, J. Am. Chem. Soc. 2004, 126, 8466-8476.

Moss, R. A.; Ma, Y.; Sauers, R. R.; Madni, M. “The Nortricyclyl-Norbornenyl Cation System Accessed by Carbene Fragmentation,” J. Org. Chem. 2004, 69, 3628-3634.

Sauers, R. R.; Van Arnum, S. D. “g-Hydroxy Alkynyl Ketones as Useful Scaffolds for the Preparation of Combinatorial Libraries of Furans, Isoxazoles and Pyrazoles,” J. Comb. Chem. 2004, 6, 350-365.

Haubenstock, H, Sauers, R. R. "Computational Studies of Vinyl-substituted Halonium Ions," Tetrahedron 2004, 60, 1191-1196.

Sauers, R. R.; Van Arnum, S. D. “A Convenient Preparation of 3-Acetyl-5-methylisoxazole,” J. Heterocyclic Chem. 2003, 40, 655-658.

Sauers, R. R.; Van Arnum, S. D. “A Thio-Staudinger Reaction: Thermolysis of a Vinyl Azide in the Presence of t-Butyl Mercaptan,” Phosphorus, Sulfur, and Silicon and the Related Elements 2003, 178, 2169-2181.