1. Accurate Equilibrium Structures of Piperidine and Cyclohexane JEAN DEMAISON, Laboratoire de Physique de Lasers, Atomes et Molécules, Université de Lille 1, 59655 Villeneuve d’Ascq Cedex, France NORMAN C. CRAIG, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074 USA PETER GRONER, Department of Chemistry, University of Missouri – Kansas City, Kansas City, MO 64110 USA PATRICIA ÉCIJA and EMILIO J. COCINERO, Departamento de Química Física, Facultad de Ciencia y Tecnología, Universidad del País Vasco (UPV-EHU), Ap. 644, E- 48080 Bilbao, Spain ALBERTO LESARRI, Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain HEINZ DIETER RUDOLPH, Department of Chemistry, University of Ulm, D-89069 Ulm, Germany

2. Piperidine C s symmetry 25 parameters Cyclohexane D 3d symmetry 6 parameters

3. MW Transitions for Isotopologues of Piperidine Species Transitions LiteratureNewTotal normal79 a,b 1392 2- 13 C 1 32 c 32 3- 13 C 1 13 c 1023 4- 13 C 1 11 c 718 15 N 4 4 ND 7 b.d 7 a Parkin, J. E.; Buckley, P. J.; Costain, C. C. J. Mol. Spectrosc. 1981, 89, 465-483. b Ehrlichmann, H.; Grabow, J.-U.; Dreizler, H.; Heineking, N.; Andolfatto, M. Z. Naturforsch. A 1989, 44, 841-847. c Spoerel, U.; Stahl, W. Chem. Phys. 1998, 239, 97-108. d Using frequencies deperturbed for quadrupole coupling. 24 rotational constants fit to transitions with initial centrifugal distortion constants computed with the MP2/cc-pVTZ model.

4. MW Transitions for Piperidine

5. MW Transitions for Isotopologues of Cyclohexane SpeciesTransitions Literature a 1,1-d 2 41 1- 13 C 1 -1,1-d 2 24 1-d 1 -eq 39 1-d 1 -ax 7 1,1,2,2,3,3-d 6 131 a Dommen, J.; Brupbacher, Th.; Grassi, G.; Bauder, A.. J. Amer. Chem. Soc. 1990, 112, 953-957. One rotational constant (A 0 = B 0 ) found for the d 0 and d 12 species by rotational Raman spectroscopy. b One rotational constant found for the d 0 species by Raman coherence spectroscopy. c b Peters, R. A.; Walker, W. J.; Weber, A. J. Raman Spectrosc. 1973, 1, 159-176. C Brügger, G.; Frey, H.-M.; Steinegger, P.; Kowalewski P.; Leutwyler, S. J. Phys. Chem. A 2011, 115, 12380-12389.

6. Equilibrium Rotational Constants From GS rot. consts. with adjustments for vib-rot interaction (MP2/cc- pVTZ) and a small electronic contribution [B3LYP/6-311+G(3df,2pd)] Predicate Structures Piperidine and Cyclohexane r e = r{CCSD(T)/cc-pVTZ(FC) + MP2/[cc-pVQZ(FC) – cc-pVTZ(FC) + cc-pwCVQZ(AE) – cc-pwCVQZ(FC)} Cyclohexane – in close agreement r e = r{CCSD(T)/cc-pwCVTZ(AE) + MP2/[cc-pwVQZ(AE) – cc-pVTZ(AE)]} Mixed Estimation Concurrent fit to equilibrium rotational constants and predicate structural parameters, each set with appropriate uncertainties.

7. Structure Fitting Detects Faulty MW Assignments through poor fit of some rotational constants Pip-3- 13 C 1 Pip-4- 13 C 1 lines for 3 13 - 2 12 lines for 3 03 – 2 02 ca 17023 MHz (lit.) ca 17020 MHz (lit.) P b = Σ m i b i 2 P b (pred) = 97.152 u Å 2 P b (obs) = 97.174 u Å 2

8. Comparative Bond Lengths/Å PiperidineCyclohexane N-H1.012 N-C21.459 C2-Hx1.102 C2-Hq1.090 C2-C31.521 C3-Hx1.092 C3-Hq1.091 C3-C41.526 C4-Hx1.0941.096 C4-Hq1.091

9. Conclusions Improved MW observations for isotopologues of piperidine. Equilibrium structures for piperidine and cyclohexane (0.001 Å, 0.2°). Structure fitting detects faulty MW assignments. Impact of nitrogen atom substitution on the bond parameters in cyclohexane.

10. Acknowledgments Ohio Supercomputer Center. Oberlin College. Spanish MICINN and MINECO (CTQ2011-22923, CTQ2012-39132). Basque Government (IT520-10) and UPV/EHU (UFI 11/23). Research facilities from the SGI/IZO-SGIker.