Natural substances Gasphase structures of linalool and coumarin

Natural substances Gas-phase structures of linalool and coumarin studied by microwave spectroscopy Ha Vinh Lam NGUYEN RWTH Aachen University, Germany

Experimental technique Molecular beam Fourier transform microwave (MB-FTMW) spectrometers Frequency ranges: 4 to 26. 5 GHz (big cavity) 26. 5 to 40 GHz (small cavity)

Experimental technique High resolution mode Scan mode

Large Amplitude Motion

Molecular Biology • Structure – odor relationship (interaction between molecules and receptors) • Gas-phase structure studies are important, since the sense of smell starts from gas-phase molecules. • Molecular modelling to predict the smell of a substance from its gas-phase structure.

Linalool – a touch of lavender H. V. L. Nguyen, H. Mouhib, S. Klahm, W. Stahl, I. Kleiner, Phys. Chem. Phys. 15, 10012 -10018 (2013).

Essence de lavendin (Provence, France) Linalool (Sigma Aldrich, Germany) MHz

• First acyclic monoterpene investigated by microwave spectroscopy. • Only the splittings due to internal rotation of methyl group 2 could be resolved. • Globular rather than prolate structure.

Coumarin – woodruff scent • Flavor substance in food industry • Aromatic, planar, dipole moments in a- and bdirections • All nine 13 C isotopologues could be measured in their natural abundances. Assignment in progress. Collaboration with J. -U. Grabow, institute for physical chemistry and electrochemistry,

Coumarin MW spectrum Recorded in Hannover

Fitted structure parameters Parameter Unit Main isotopologue Calc. a A GHz 2. 83036962(22) 2. 8195 B GHz 0. 88558201(13) 0. 8800 C GHz 0. 67479588(12) 0. 6707 ΔJ k. Hz 0. 0148(14) ΔJK k. Hz 0. 0231(38) J k. Hz 0. 00362(14) N σ 20 k. Hz 1. 2 • Assignment of all nine 13 C isotopologues have to be carried out at the same time.

Conclusion • A combination of microwave spectroscopy and quantum chemical calculation is an excellent tool for study the structures and dynamics of odorant molecules and natural substances in the gas-phase. • The structure of the major component of lavender oil, linalool, and coumarin was investigated. In linalool, the Internal rotation of a methyl group could be resolved and fitted. • Information obtained from internal rotation is important for an unambiguous conformer identification.

Thank you for your attention! • Jens-Uwe Grabow • Isabelle Kleiner