Broadband Microwave Spectroscopy to Study the Structure of Odorant Molecules and of Complexes in the Gas Phase Sabrina Zinn, Chris Medcraft, Thomas Betz, Melanie Schnell Max Planck Institute for the Structure and Dynamics of Matter at the Center for Free-Electron Laser Science, Hamburg/Germany The Hamburg Centre for Ultrafast Imaging, Hamburg/Germany

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter experimental setup 2 chirp 2.0 – 8.5 GHz supersonic expansion horn antennas resolution 20 kHzup to 50 µs FID 4-aminobenzonitrile (Brown et al., Rev. Sci. Instrum. 79, (2008))

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter 3 trans-cinnamaldehyde (2E)-3-phenylprop-2-enal motivation odorant molecule conjugated π-electron system expansion of former microwave study (Steinmetz et al., J. Am. Chem. Soc. 96, 685 (1974))

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter spectrum and fit GHz

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter 5 spectrum and fit

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter trans-cinnamaldehyde constants 6 parameterexperimental calculation B3LYP* calculation MP2* Steinmetz et al** A [MHz] (2) B [MHz] (2) C [MHz] (2) B+C [MHz] (4) (1) D K [kHz]1.6(2)1.2 D JK [kHz]0.07(2)0.08 D J [kHz]0.006(1)0.008 J max 17 assigned lines93 error [kHz]6.5 * G(2d,2p) **(Steinmetz et al., J. Am. Chem. Soc. 96, 685 (1974))

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter structure determination 30 rotational constants 7 r s substitution structure r 0 effective ground state structure r m mass dependent structure (using PROSPE /Z. Kisiel; atom positions, bond length and bond angles

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter inertial defect 8 for perfectly planar molecules for trans-cinnamaldehyde ° °

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter structure determination 30 rotational constants 9 r s substitution structure r 0 effective ground state structure r m mass dependent structure (using PROSPE /Z. Kisiel; atom positions, bond length and bond angles

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter **MP2/ G(2d,2p) (15) 1.387(7) 1.413(28) 1.451(20) 1.342(26) 1.461(14) 1.409(18) 1.402(7) 1.409(22) C-C 1.53 Å C=C 1.34 Å structure determination calculated** r m -structure bond lengths in Å

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter (26) 1.461(14) **MP2/ G(2d,2p) 121.3°(59) 119.7° ° (4) 1.468(4) 1.340(7) 1.478(6) 119.7°(3) 121.5°(6) s-trans-acrolein* s-trans-trans-cinnamaldehyde s-cis-trans-cinnamaldehyde s-cis-acrolein* *Blom et al., J. Am.Chem. Soc., 106, 7427 (1984) structure determination calculated** experimental bond lengths in Å

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter summary  two conformers of trans-cinnamaldehyde were found  precise structure determination of the low energy conformer  electronic configuration in the side chain is independent of the aromatic ring  electronic repulsion causes the energy difference of the two conformers 12

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter weakly bound complexes 13 Glucose Tryptophan Glycolaldehyde Dimer Diphenylether Methanol

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter glycolaldehyde dimer 14 motivation smallest sugar monomer was found in space interaction between open chain carbohydrates

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter 15 glycolaldehyde dimer (Altnöder et al., Chemistry Open, 1, 269 (2012)) φ/° D el / kJ mol -1

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter 16 parameterexperimental calculation MP2* calculation B3LYP-D3** A [MHz] (1) B [MHz] (8) C [MHz] (8) parent C1 C2 O1 O2 glycolaldehyde dimer C1 C2 O1 O2 * aug-cc-pVTZ ** def2-TZVP measurement simulation

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter 17 Experiment = 2.869(3) Å MP2* = Å B3LYP-D3** = Å  detailed analysis of the structure will follow glycolaldehyde dimer O-O distances: * aug-cc-pVTZ ** def2-TZVP

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter Methanol Diphenylether diphenylether-methanol complex 18 parameterexperimental calculation B2PLYP-D3* A [MHz] (25) B [MHz] (4) C [MHz] (3) *def2-TZVP monomer complex

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter summary & outlook  microwave spectroscopy is an ideal tool to study the structure of molecules and complexes  robust technique with a high sensitivity  different methods to determine the structure  further analysis of the new data of the weakly bound complexes Glucose Tryptophan

Structure Determination of trans-Cinnamaldehyde and of Weakly Bound Complexes Max Planck Institute for the Structure and Dynamics of Matter Acknowledgement  Funding:  Max Planck Research Group: Structure and Dynamics of Cold and Controlled Molecules  Thank you for your attention! 20 David Schmitz