BROADBAND MICROWAVE SPECTROSCOPY AS A TOOL TO STUDY DISPERSION INTERACTIONS IN CAMPHOR-ALCOHOL SYSTEMS MARIYAM FATIMA, CRISTÓBAL PÉREZ, MELANIE SCHNELL, Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany

Non-Covalent Interactions Water Amino Acid Guanine Cytosine

Molecule of Interest : Camphor-Alcohol System Z. Kisiel et al., Phys. Chem. Chem. Phys. 5(2003), 820 Side view: Camphor Camphor Methanol Ethanol

Camphor-Water System 2 isomers for camphor-water were observed using rotational spectroscopy 3 1 2 3 possibilities where water can form a complex with camphor. Isomer 1 Isomer 2 Camphor-(H2O) C.Pérez et al., J. Phys. Chem. Lett., 7 (1) (2016), 154–160

Chirped Pulse Microwave Spectroscopy in Hamburg Sample introduction 2-8 GHz 20 kHz linewidth Microwave Horn Antenna (Receiver) Supersonic Expansions Microwave Horn Antenna (Emitter) Backing pressure of neon: 3.2 bar Temperature for camphor: 100 ° C

PART 1: CAMPHOR-METHANOL

Camphor-Methanol: Ab initio Results ∆E = 0 kJ/mol ∆E ≈ 1 kJ/mol Level of theory: B3LYP-D3/aug-cc-pvtz

Camphor-Methanol: Experimental Spectrum Isomer 1

Camphor-Methanol: Rotational Constants Isomer 1 ∆E=0 kJ/mol B3LYP-D3 Dipole Moment (D) A (MHz) 1337.09 3.3 B (MHz) 441.38 0.4 C (MHz) 429.50 -0.1 Isomer 2 B3LYP-D3 Dipole Moment (D) A (MHz) 1341.61 -4.0 B (MHz) 450.59 1.0 C (MHz) 434.39 0.2 ∆E=1 kJ/mol

Camphor-Methanol: Splitting Patterns

Internal Rotation in Methanol Internal rotation barrier height E Internal rotation barrier = 3.2 kJ/mol A A E E A

Internal Axis Method x Internal rotation axis z y XIAM Program: uses internal axis method predict and fits the rotational spectrum of an asymmetric molecule having internal rotors Internal rotation barrier = 2.4534(21) kJ/mol   H.Hartwig et al., Z. Naturforsch 51a (1996), 923-932

Camphor-Methanol: Results 606←505 66 a-type transitions assigned 606←505 E 624←523 606←505 A 625←524 A A E Isomer 1

Camphor-Methanol: Results Internal rotation barrier = 2.4534(21) kJ/mol Isomer 1

PART 2: CAMPHOR-ETHANOL

Camphor-Ethanol 3 conformations of ethanol Gauche ∆E=0.5 kJ/mol Trans Z. Kisiel et al., Phys. Chem. Chem. Phys. 5(2003), 820 Hearn et al., J. Chem. Phys. 123 (2005), 134324

Camphor-Ethanol: Ab initio Results Level of theory: B3LYP-D3/aug-cc-pvtz ∆E≈ 0.6 kJ/mol ∆E≈ 0.7 kJ/mol Isomer 3 Isomer 2 ∆E=0 kJ/mol Isomer 1

Camphor-Ethanol: Experimental Spectrum Ethanol dimer 1, Ethanol dimer 2, Ethanol dimer 3 Isomer 1, Isomer 2, Isomer 3, Isomer 4

Camphor-Ethanol: Experimental Spectrum Isomer 1, Isomer 2, Isomer 3, Isomer 4

Camphor-Ethanol: Results Isomer 1

Camphor-Ethanol: Results Isomer 2

Camphor-Alcohol: Summary Camphor-methanol Camphor-ethanol Isomer 1 Isomer 1 Isomer 2 Only gauche conformation of ethanol was found. No internal rotation in camphor-ethanol. 3 1 2 ROLE OF DISPERSION INTERACTION???

Camphor-Ethanol (Isomer 1) Camphor-Ethanol (Isomer 2) Symmetry Adapted Perturbation Theory Eint = EAB - EA - EB Energy Decompositions (kJ/mol ) from a SAPT(0)/jun-cc-pVDZ (Water)2 Camphor-Water Camphor-Methanol (Isomer 1) Camphor-Ethanol (Isomer 1) Camphor-Ethanol (Isomer 2) ∆Eelst -8.90 -49.2 -49.4 -46.79 -46.6 ∆Eind -2.40 -14.6 -13.3 -13.2 ∆Edisp -1.35 -11.6 -19.6 -20.4 ∆Eexch 8.17 43.6 43.7 47.4 48.7 ∆Etot -4.47 -31.8 -31.9 -32.4 -31.6

Conclusion and Outlook The extent of hydrogen bonding is decreasing while the dispersion interaction is increasing. To identify complexes of camphor ethanol. Further work on camphor-propanol complexes will be done to see the effect of dispersion interactions.

Acknowledgements

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