A pulsed molecular beam Fourier transform microwave spectrometer operating in the frequency range 2 - 26.5 GHz was used to measure the spectrum of phenetole (ethyl phenyl ether or ethoxybenzene, C₆H₅OC₂H₅). The conformational landscape is completely determined by the orientations of the phenyl ring and the ethyl group. A two-dimensional potential energy surface was calculated at the MP2/6-311++G(d,p) level of theory. Two conformers were found: The trans conformer has a C_s symmetry, and the gauche conformer has the ethyl group tilted out of the phenyl plane by about 70^°. Totally 186 rotational transitions were assigned to the more stable planar trans conformer, and fitted using a semi-rigid rotor model to measurement accuracy of 2 kHz. Highly accurate rotational and centrifugal distortion constants were determined. Several method and basis set combinations were applied to check for convergence and to compare with the experimentally deduced molecular parameters. The inertial defect of the observed conformer ∆_c = (I_c - I_a - I_b) = -6.718 uŲ confirms that the heavy atom skeleton is planar with two pairs of hydrogen atoms out of plane. All lines in the spectrum could be assigned to the trans conformer, which confirms that the gauche conformer cannot be observed under our measurement conditions. In agreement with the rather high torsional barrier of the methyl group (V₃ = 1168 cm⁻¹) calculated by quantum chemical methods, all assigned lines appeared sharp and no signs of splittings were observed for the methyl internal rotation.

l0pt Figure The pure rotational spectrum of a Claisen rearrangement precursor, allyl phenyl ether (APE), has been measured on a chirped pulse Fourier transform microwave (CP-FTMW) spectrometer in the 8-14 GHz region. Rotational and centrifugal distortion constants for multiple conformations have been determined for the first time and will be discussed. This is the first study of a phenyl-containing ether where multiple conformers were experimentally observed all within their ground vibrational states. Quantum chemical calculations have been performed to isolate low energy geometries of APE and are implemented to aid in spectral assignment. Other structural parameters such as planar moments and inertial defects for the APE conformers are presented and compared to similar molecules for discussion.

The planarity of five-membered rings is derived from a competition between ring-angle strain and stability of the torsional angles. The planar form maximizes the already stressed, smaller-than-normal, C-C bond angles, while puckering reduces the unfavorable eclipsed interactions. The structure, dynamics, and planarity of three anhydrides, succinic, methylsuccinic, and methylene (itaconic) anhydride, were studied and compared using chirped-pulse Fourier transform microwave spectroscopy.

The ground states of 2-fluorophenol (2-FPh) and 3-fluorophenol (3-FPh) were studied using Fourier transform microwave (FTMW) techniques to record their rotational spectra in the range of 6 to 26 GHz. Two planar conformers of similar energy were observed for 3-FPh (cis, trans) while only the lowest energy conformer (cis) of 2-FPh was observed due to the stabilizing effect of an intramolecular interaction between fluorine and OH. Rotational constants derived from spectra of the ¹³C analogs, observed in natural abundance, were used to calculate the substitution (r_s) and effective ground state (r₀) parameters for cis-2-FPh and trans-3-FPh in order to study the effect of fluorination at sites along the benzene backbone. Geometry optimization at the MP2/6-311++G(2d,2p) level was used obtain the equilibrium (r_e) structures for comparison. Furthermore, natural bond order (NBO) calculations provided supporting information of a OH•••F interaction in cis-2-FPh.

Structural signatures for exo-anomeric effect have been extracted from the archetypal methyl-β-D-xyloside using broadband Fourier transform microwave spectroscopy combined with laser ablation. Spectrum analysis allows the determination of a set of rotational constants, which has been unequivocally attributed to conformer cc-β-⁴C₁ g-, corresponding to the global minimum of the potential energy surface, where the aglycon residue (CH₃) orientation contributes towards maximization of the exo-anomeric effect. Further analysis allowed the determination of the r_s structure, based on the detection of eleven isotopologues - derived from the presence of six ¹³C and five ¹⁸O atoms - observed in their natural abundances. The observed glycosidic C₁-O₁ bond length decrease (1.38 Å) can be interpreted in terms of the exo-anomeric effect. As such, the exo-anomeric effect presents itself as one of the main driving forces controlling the shape of many biologically important oligosaccharides.

r0pt Figure The microwave spectra for seven unique isotopologues of BN-naphthalene (4a,8a-azaboranaphthalene) were measured using a pulsed-beam Fourier transform microwave spectrometer. Spectra were obtained for the normal isotopologues with ¹⁰B, ¹¹B, all unique single ¹³C and the ¹⁵N isotopologue, in natural abundance. The rotational, centrifugal distortion and quadrupole coupling constants determined for the ¹¹B¹⁴N isotopologue are A = 3042.7128(4) MHz, B = 1202.7066(4) MHz, C = 862.2201(4) MHz, D_J = 0.06(1) kHz, 1.5 eQq_aa (¹⁴N) = 2.578(6) MHz, 0.25(eQq_bb- eQq_cc) (¹⁴N) = -0.119(2) MHz, 1.5 eQq_aa (¹¹B) = -3.922(8) MHz, and 0.25(eQq_bb- eQq_cc) (¹¹B) = -0.907(2) MHz. The experimental inertial defect is ∆ = -0.159 amu Ų, which is consistent with a planar structure. The B-N bond length is 1.47 Å, indicating π-bonding character. The results are compared with similar results for B-N bonding in 1,2-dihydro-1,2-azaborine and BN-cyclohexene.

The emission of volatile organic compounds, from plants has strong revelance for plant physiology, plant ecology and atmospheric chemistry.R. Baraldi, F. Rapparini, O. Facini, D. Spano and P. Duce, Journal of Mediterranean Ecology, Vol.6, No.1, (2005).amphene (C₁₀H₁₆) is a bicyclic monoterpene which is emitted in the atmosphere by biogenic sources.A. Bracho-Nunez, N. M. Knothe, S. Welter, M. Staudt, W. R. Costa, M. A. R. Liberato, M. T. F. Piedade, and J. Kesselmeier Biogeosciences, 10, 5855-5873, (2013).Minna Kivimäenpää, Narantsetseg Magsarjav, Rajendra Ghimire, Juha-Matti Markkanen, Juha Heijari, Martti Vuorinen and Jarmo K. Holopainen, Atmospheric Environment, 60, 477-485, (2012). The structure of the unique stable conformer was optimized using density functional theory and ab initio calculations. The rotational spectrum of camphene was recorded in a supersonic jet expansion with a Fourier transform microwave spectrometer over the range 2-20 GHz. Signals from the parent species and from the ten ¹³C isotopomers were observed in natural abundance. The rotational and centrifugal distortion parameters were fitted to a Watson’s Hamiltonian in the A-reduction. A magnetic hyperfine structure associated with the pairs of hydrogen nuclei in the methylene groups was observed and modeled.
The rotational constants coupled to the equilibrium structure calculations were used to determine the r₀ and the r_m⁽¹⁾ gas-phase geometries of the carbon skeleton. The present work provides the first spectroscopic characterization of camphene in the gas phase and these results are also relevant for ozonolysis kinetics study through Criegee intermediates.R.C. de M. Oliveira and G. F. Bauerfeldt, J. Phys. Chem. A, 119 2802-2812 (2015).

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R. Baraldi, F. Rapparini, O. Facini, D. Spano and P. Duce, Journal of Mediterranean Ecology, Vol.6, No.1, (2005).C A. Bracho-Nunez, N. M. Knothe, S. Welter, M. Staudt, W. R. Costa, M. A. R. Liberato, M. T. F. Piedade, and J. Kesselmeier Biogeosciences, 10, 5855-5873, (2013).

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R.C. de M. Oliveira and G. F. Bauerfeldt, J. Phys. Chem. A, 119 2802-2812 (2015).

We have previously conducted rotational studies of several tropanes, E. J. Cocinero, A. Lesarri, P. Écija, J.-U. Grabow, J. A. Fernández, F. Castaño, Phys. Chem. Chem. Phys. 2010, 49, 4503^, P. Écija, E. J. Cocinero, A. Lesarri, F.  J.  Basterretxea, J. A. Fernández, F. Castaño, Chem. Phys. Chem. 2013, 14, 1830^, P. Écija, M.  Vallejo-Lopez, I.  Uriarte, F.  J.  Basterretxea, A. Lesarri, J. A. Fernández, E. J. Cocinero, submitted 2016ince this bicyclic structural motif forms the core of different alkaloids of pharmaceutical interest. Now we report on the conformational properties and molecular structure of pseudo-pelletierine (9-methyl-9-azabicyclo[3.3.1]nonan-3-one), probed in a jet expansion with Fourier-transform microwave spectroscopy. Pseudo-pelletierine is an azabicycle with two fused six-membered rings, where the N-methyl group can produce inverting axial o equatorial conformations. The two conformations were detected in the rotational spectrum, recorded in the region 6-18 GHz. Unlike tropinone and N-methylpiperidone, where the most stable conformer is equatorial, the axial species was found dominant for pseudo-pelletierine. All monosubstituted isotopic species (¹³C, ¹⁵N and ¹⁸O) were identified for the axial conformer, leading to an accurate determination of the effective and substitution structures. An estimation of conformational populations was derived from relative intensities. The experimental results will be compared with ab initio (MP2) and DFT (M06-2X, B3LYP) calculations.

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E. J. Cocinero, A. Lesarri, P. Écija, J.-U. Grabow, J. A. Fernández, F. Castaño, Phys. Chem. Chem. Phys. 2010, 49, 4503\end P. Écija, E. J. Cocinero, A. Lesarri, F.  J.  Basterretxea, J. A. Fernández, F. Castaño, Chem. Phys. Chem. 2013, 14, 1830 P. Écija, M.  Vallejo-Lopez, I.  Uriarte, F.  J.  Basterretxea, A. Lesarri, J. A. Fernández, E. J. Cocinero, submitted 2016s

New measurements of microwave lines (A and E) of propene and its three ¹³C₁ isotopologues have been made in the 10-22 GHz region with FT accuracy. The revised lines for propene along with many hundreds from the literature were fitted with the ERHAM program for internal rotors to give improved rotational constants. The new constants for propene are A₀ = 46280.2904(16), B₀ = 9305.24260(30), and C₀ = 8134.22685(28) MHz. Lines for the 3-¹³C₁ species were observed in a pure sample; lines for the 1-¹³C₁ and 2-¹³C₁ species were observed in natural abundance. In fitting the limited sets of lines for the ¹³C₁ species, many of the centrifugal distortion constants and most of the tunneling parameters were transferred from the fit of propene itself with 27 parameters. Improved rotational constants for the ¹³C₁ species are reported.

Propene-3-d₁ has two conformers: a single sy conformer with the CD bond eclipsing the C=C bond; two equivalent asy conformers with the CD bond out of the symmetry plane of the sy conformer. In the MW spectrum the sy conformer has single transitions of a semi-rigid rotor. The asy conformer has (+) and (-) transitions as a consequence of tunneling. A MW investigation with FT accuracy and sensitivity was done in the 10-22 GHz region, where the light propene molecule has relatively few transitions strong enough to be observed. The lines were split by deuterium quadrupolar coupling. Rotational constants for the sy species are: A₀ = 40582.1(2), B₀ = 9067.04(1), and C₀ = 7766.02(1) MHz. We have observed the (+) and (-) transitions for the asy conformer in the same spectral region. Rotational constants fit to the averages of these lines are: A₀ = 43403.8(1), B₀ = 8659.00(2), and C₀ = 7718.24(2) MHz. In fitting for both conformers, the cw lines observed by Lide and Christensen for J = 1 to 2; K_a = 0, 1 transitions were used to strengthen the data sets.D. R. Lide, Jr and D. Christensen, J. Chem. Phys. 35, 1374-1378 (1961).hese new rotational constants will be used in determining a semiexperimental equilibrium structure for propene.

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D. R. Lide, Jr and D. Christensen, J. Chem. Phys. 35, 1374-1378 (1961).T

The preferred conformation of cis-1,3-butadiene (CH₂=CH−CH=CH₂) has been of long-standing importance in organic chemistry because of its role in Diels-Alder transition states. The molecule could adopt a planar s-cis conformation, in favor of conjugations in the carbon chain, or a non-planar gauche conformation, as a result of steric interactions between the terminal H atoms. To resolve this ambiguity, we have now measured the pure rotational spectrum of this isomer in the microwave region, unambiguously establishing a significant inertial defect, and therefore a gauche conformation. Experimental measurements of gauche-1,3-butadiene and several of its isotopologues using cavity Fourier-transform microwave (FTMW) spectroscopy in a supersonic expansion and chirped-pulse FTMW spectroscopy in a 4 K buffer gas cell will be summarized, as will new quantum chemical calculations.

Synthetic foldamers are non-natural polymers designed to fold into unique secondary structures that either mimic nature’s preferred secondary structures, or expand their possibilities. Among the most studied synthetic foldamers are β-peptides, which lengthen the distance between amide groups from the single substituted carbon spacer in α-peptides by one additional carbon. We present data on a mixed α/β tri-peptide in which a single β-residue with a conformationally constrained cis-2-aminocyclohexanecarboxylic acid (cis-ACHC) substitution is inserted in an α-peptide backbone to form Ac-Ala-β-ACHC-Ala-NHBn. This αβα structure is known in longer sequences to prefer formation of a 9/11 mixed helix. Under isolated, jet cooled conditions, four unique conformers were observed in the expansion. The dominant conformer is configured in a tetramer cycle with every amide carbonyl and amine group involved in hydrogen bonding, giving rise to a tightly folded C12/C7/C8/C7 structure reminiscent of a β-turn. This talk will describe the conformation specific IR and UV spectroscopy methods used to study this mixed peptide, as well as its experimentally observed conformational preferences.

Rotational spectra for gauche-1,2-dichloroethane (12DCE), gauche-1-chloro-2-fluoroethane (1C2FE) and both anti- and gauche-2,3-dichloropropene (23DCP) have been observed using chirped-pulse Fourier-transform microwave (FTMW) spectroscopy in the 6-18 GHz region. Although the anti conformers for all three species are predicted to be more stable than the gauche forms, they are nonpolar (12DCE) or nearly nonpolar (predicted dipole components for anti-1C2FE: μ_a = 0.11 D, μ_b = 0.02 D and for anti-23DCP: μ_a = 0.25 D, μ_b = 0.02 D); nevertheless, it was also possible to observe and assign the spectrum of anti-23DCP. Assignments of parent spectra and ³⁷Cl and ¹³C substituted isotopologues utilized predictions at the MP2/6-311++G(2d,2p) level and Pickett's SPCAT/SPFIT programs. For the weak anti-23DCP spectra, additional measurements also utilized a resonant-cavity FTMW spectrometer. Full chlorine nuclear quadrupole coupling tensors for gauche-12DCE and both anti- and gauche-23DCP have been diagonalized to allow comparison of coupling constants. Kraitchman's equations were used to determine r_s coordinates of isotopically substituted atoms and r₀ structures were also deduced for gauche conformers of 12DCE and 1C2FE. Structural details and chlorine nuclear quadrupole coupling constants of all three molecules will be compared, and effects of differing halogen substitution and carbon chain length on molecular properties will be evaluated.

Herein we present experimentally determined infra-red spectra of entrance channel complexes of various small alkanes interacting with alkanes. The entrance channel complexes of ethane, propane and n-butane with positively charged aluminum ions were studied in the gas phase. The spectra are compared with theoretical calculations, and the structures of various products are elucidated from the spectra.

Transition metal complexes play an important role in coordination chemistry as well as in the formation of metal-based drugs. In order to obtain accurate results for studying these type of complexes quantum chemical studies are performed and especially density functional theory (DFT) has become a promising choice. This talk represents molecular structures, charge distributions and vibrational analysis of Ni(II), Zn(II), and Cd(II) iodide complexes of p-toluidine and m-toluidine by means of DFT. Stable structures of the ligands and the related complexes have been obtained in the gas phase at B3LYP/def2-TZVP level and calculations predict Ni(II) complexes as distorted polymeric octahedral whereas Zn(II) and Cd(II) complexes as distorted tetrahedral geometries. Charge distribution analysis have been performed by means of Mulliken, NBO and APT methods and physically most meaningful method for our compounds is explained. Vibrational spectra of the title compounds are computed from the optimized geometries and theoretical frequencies are compared with the previously obtained experimental data. Since coordination occurs via nitrogen atoms of the free ligands, N-H stretching bands of the ligands are shifted towards lower wavenumbers in the complexes whereas NH₂ wagging and twisting vibrations are shifted towards higher wavenumbers.