1. SEMIEXPERIMENTAL EQUILIBRIUM STRUCTURES FOR THE EQUATORIAL CONFORMERS OF N- METHYLPIPERIDONE AND TROPINONE BY THE MIXED ESTIMATION METHOD JEAN DEMAISON, Laboratoire de Physique des Lasers, Atomes et Molécules, Université de Lille I, 59655 Villeneuve d'Ascq Cedex, France NORMAN C. CRAIG, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074 EMILIO J. COCINERO, Departamento de Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Ap. 644, E-48080 Bilbao, Spain JENS-UWE GRABOW, Institut für Physikalische Chemie and Elektrochemie, Lehrgebiet A, Gottfried-Wilhelm-Leibniz Universität, Callinstrasse 3A, D-30167 Hannover, Germany ALBERTO LESARRI, Departamento de Química Física y Química Inorgínica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain H. D. RUDOLPH, Department of Chemistry, University of Ulm, D-89069 Ulm, Germany

2. Preliminary Mixed estimate structure for cis,trans-1,4-difluorobutadiene a 17 parameters; rot. consts. for each 13 C and 2 H species from MW a Demaison, J. F.; Craig, N. C. J. Phys. Chem. A 2011, 115, 8049-8054.

3. N-methylpiperidone tropinone

4. N-Methylpiperidone (19 atoms) plane of symmetry 28 parameters: 11 bond lengths, 17 bond angles Tropinone (23 atoms) plane of symmetry 34 parameters: 14 bond lengths, 20 bond angles

5. Ground state rotational constants from microwave spectroscopy with natural abundance for all the different heavy atom substitutions. 1,2 Converted to equilibrium rotational constants by vibration-rotation constants (alphas) computed with the quadratic and cubic force constants from a B3LYP/cc- pVTZ model. At most 1% adjustments. Peter Groner did these calculations with his VIBROT program. 1 N-Methylpiperidone. Evangelisti, L.; Lesarri, A.; Jahn, M. K.; Cocinero, E. J.; Caminati, W.; Grabow, J.-U. J. Phys. Chem. A 2011, 115, 9545-9551. 2 Tropinone. Cocinero, E.J.; Lesarri, A.; Écija, P.; Grabow, J.-U.; Fernández, J. A.; Castaño Phys. Chem. Chem. Phys. 2010, 12, 6076-6083.

8. Mixed estimation method for semiexperimental structures a Predicate values for bond lengths and bond angles derived from QC calculations (MP2/cc- pVTZ model) after applying a correction for the C=O bond. The correction came from comparing predictions with equilibrium values for various small molecules. Concurrent fit of predicate values with appropriate uncertainties and of equilibrium rotational constants with appropriate (tighter) uncertainties. A stepwise process. a A similar method was first applied in electron diffraction. L. S. Bartell, D. J. Romanesko, T. C. Wong, in: Chemical Society Specialist Periodical Report No. 20: Molecular Structure by Diffraction Methods, Sims, G. A.; Sutton, L. E., Eds., The Chemical Society London, 1975, Vol. 3, pp. 72- 79.

9. Uncertainties Predicates CH bond lengths: ±0.002 Å Heavy atom bond lengths: ±0.003 Å Bond angles: ±0.3° Torsion angles: ±0.5° Equilibrium rotational consts.: ±0.02 MHz too small but gives relatively greater weight

13. N-methylpiperidone tropinone

14. Conclusions Rotational constants are available from MW spectroscopy for heavy atom substitutions in natural abundance. An equilibrium structure for the heavy atom backbone obtained by the Kraitchman substitution method is usually flawed. The mixed estimation method, in which calculated internal coordinates (  ) and “observed” equilibrium rotational constants (  ) are fit concurrently, yields good semiexperimental equilibrium structures. This method has been illustrated with N- methylpiperidone and tropinone. Good agreement with the structure predicted by the MP2/cc-pVTZ model with a few exceptions.

15. Acknowledgements Peter Groner, University of Missouri- Kansas City Oberlin College, Department of Chemistry and Biochemistry National Science Foundation for support of the Beowulf computer cluster at Oberlin College