73 rd Annual International Symposium on Molecular Spectroscopy

73 rd Annual International Symposium on Molecular Spectroscopy CP-FTMW Spectroscopy of the Low Energy Conformers of Two Chiral Alcohols: Myrtenol and Nopol Galen Sedo – The University of Virginia’s College at Wise Frank E. Marshall & Garry S. Grubbs II – Missouri University of Science and Technology TC 09 June 19 th, 2018 1

73 rd Annual International Symposium on Molecular Spectroscopy Rotational Spectroscopy of Chiral Bicyclic Monoterpenes α-pinene 1 verbenone 2 myrtenol 3 1 E. M. Neeman et al. , J. Chem. Phys. 147 (2017) 214305 2 F. E. Marshall et al. , J. Mol. Spectrosc. 342 (2017) 109 3 M. Chrayteh et al. , J. Mol. Spectrosc. 336 (2017) 22 Camphene, camphor, fenchone, norbornene, etc. TC 09 June 19 th, 2018 2

73 rd Annual International Symposium on Molecular Spectroscopy Rotational Spectroscopy of Chiral Bicyclic Monoterpenols (1 R) - (–) - Myrtenol (1 R) - (–) - Nopol Abstract: New microwave spectra of two chiral bicyclic monoterpenols have been observed using CP-FTMW spectroscopy in the 6 -18 GHz region of the electromagnetic spectrum. These spectra have given insight into the low energy conformers of the two molecules, with at least one conformer of nopol and myrtenol having been observed. Rotational constants of the assigned structures will be reported and discussed in comparison to theory. TC 09 June 19 th, 2018 3

73 rd Annual International Symposium on Molecular Spectroscopy • Previous CP-FTMW work has not observed any evidence of low energy conformers associated with the dimethyl bicyclic monoterpene body E. M. Neeman et al. , J. Chem. Phys. 147, 214305 (2017) F. E. Marshall et al. , J. Mol. Spectrosc. 342, 109 -115 (2017) M. Chrayteh et al. , J. Mol. Spectrosc. 336, 22 -28 (2017) TC 09 June 19 th, 2018 4

73 rd Annual International Symposium on Molecular Spectroscopy • Previous CP-FTMW work has not observed any evidence of low energy conformers associated with the dimethyl bicyclic monoterpene body (1 R) - (–) - Myrtenol • Inclusion of a primary alcohol group to the monoterpene introduces a new area of possible conformational diversity TC 09 June 19 th, 2018 5

73 rd Annual International Symposium on Molecular Spectroscopy TC 09 June 19 th, 2018 6

73 rd Annual International Symposium on Molecular Spectroscopy (1 R) - (–) - Myrtenol Comp 1 Comp 3 Comp 2 TC 09 June 19 th, 2018 7

73 rd Annual International Symposium on Molecular Spectroscopy Grubbs’ Group CP-FTMW Low Noise, High Fidelity Instrument • 23 GHz, 100 GS/s oscilloscope • 40 W solid state amplifier • 50 GS/s digitization rate, 20 GHz bandwidth AWG 2 -18 GHz Spectral Range • 6 GHz linear frequency sweeps (6 -12 GHz & 12 -18 GHz) • 4 μs chirp length • 20 μs FID detection TC 09 F. E. Marshall et al. , J. Mol. Spectrosc. 328, 59 (2016) June 19 th, 2018 8

73 rd Annual International Symposium on Molecular Spectroscopy TC 09 June 19 th, 2018 9

73 rd Annual International Symposium on Molecular Spectroscopy Experimentally a-type transitions dominated in all cases. TC 09 June 19 th, 2018 10

73 rd Annual International Symposium on Molecular Spectroscopy Experimentally a-type transitions dominated in all cases. TC 09 June 19 th, 2018 11

73 rd Annual International Symposium on Molecular Spectroscopy All calculations agree that this is the lowest energy conformer. Experimental intensities and the number of transitions observed would tend to agree. TC 09 June 19 th, 2018 12

73 rd Annual International Symposium on Molecular Spectroscopy MP 2 and B 3 LYP-D 3 BJ predict this to be the middle energy conformer. Experimental intensities and the number of transitions observed would tend to agree. TC 09 June 19 th, 2018 13

73 rd Annual International Symposium on Molecular Spectroscopy MP 2 and B 3 LYP-D 3 BJ predict this to be the highest energy conformer. Experimental intensities and the number of transitions observed would tend to agree. TC 09 June 19 th, 2018 14

73 rd Annual International Symposium on Molecular Spectroscopy Myrtenol Conclusions: • 3 conformers of have been assigned. • The relative energies of the conformers can not be determined from the experiment. • However, intensities and the number of observed transitions would suggest orientation: • towards the methyl groups is favorable • coplanar with the double bond is least favorable • MP 2 calculations and B 3 LYP calculations when corrected for D 3 dispersion with Becke-Johnson damping agree with this energetic progression of the conformers. TC 09 June 19 th, 2018 15

73 rd Annual International Symposium on Molecular Spectroscopy • Previous CP-FTMW work has not observed any evidence of low energy conformers associated with the dimethyl bicyclic monoterpene body (1 R) - (–) - Nopol • Inclusion of a alkyl chain and a primary alcohol group to the monoterpene introduces two new areas of possible conformational diversity TC 09 June 19 th, 2018 16

73 rd Annual International Symposium on Molecular Spectroscopy • Previous CP-FTMW work has not observed any evidence of low energy conformers associated with the dimethyl bicyclic monoterpene body (1 R) - (–) - Nopol TC 09 June 19 th, 2018 17

73 rd Annual International Symposium on Molecular Spectroscopy TC 09 June 19 th, 2018 18

73 rd Annual International Symposium on Molecular Spectroscopy B 3 LYP-D 3 BJ|def 2 -TZVP Optimized Geometries TC 09 June 19 th, 2018 19

73 rd Annual International Symposium on Molecular Spectroscopy TC 09 June 19 th, 2018 20

73 rd Annual International Symposium on Molecular Spectroscopy TC 09 June 19 th, 2018 21

73 rd Annual International Symposium on Molecular Spectroscopy Three conformers showed slight agreement with experimental constants, but only one had the expected agreement with the second moments. B 3 LYP-D 3 BJ|def 2 -TZVP TC 09 June 19 th, 2018 22

73 rd Annual International Symposium on Molecular Spectroscopy Three conformers showed slight agreement with experimental constants, but only one had the expected agreement with the second moments. B 3 LYP-D 3 BJ|def 2 -TZVP TC 09 June 19 th, 2018 23

73 rd Annual International Symposium on Molecular Spectroscopy Nopol Conclusions: • 2 conformers have been assigned. • Comparable intensities were observed for the two spectra. • The second moments allowed both conformers to be unambiguously assigned to two of the predicted structures. • Evidence seems to suggest that placement of the alpha carbon takes precedence. TC 09 June 19 th, 2018 24

73 rd Annual International Symposium on Molecular Spectroscopy Questions? Galen Sedo – The University of Virginia’s College at Wise Frank E. Marshall & Garry S. Grubbs II – Missouri University of Science and Technology TC 09 June 19 th, 2018 25

a b Comp 1 Comp 2 a Comp 3 b a b