The millimeter wave spectrum of the Ar–CHF3 complex is measured. The microwave lines are split into two components due to tunneling between three equivalent minima. Aided by ab initio calculations, the bidimensional potential energy surface of the complex is investigated and the rotational dependence of the tunneling splitting is parameterized using an IAM-like approach. The analysis of the microwave data allows us to determine the parameters involved in this rotational dependence. The value obtained are consistent with a large amplitude motion involving a 2π/3 internal rotation of the CHF3 moiety about its threefold axis of symmetry. Information about the geometry of the intermediate configuration of this large amplitude motions is obtained.

ChemPhysChemVolume 7, Issue 3 p. 565-568 Communication Conformational Landscapes and Free-Jet Rotational Spectrum of Indan-1-ol Biagio Velino Dr., Biagio Velino Dr. Dipartimento di Chimica Fisica e Inorganica dell'Università, Viale Risorgimento 4, 40136 Bologna, ItalySearch for more papers by this authorPaolo Ottaviani Dr., Paolo Ottaviani Dr. Dipartimento di Chimica "G. Ciamician" dell' Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-2099456Search for more papers by this authorWalther Caminati Prof., Walther Caminati Prof. [email protected] Dipartimento di Chimica "G. Ciamician" dell' Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-2099456Search for more papers by this authorAnna Giardini Prof., Anna Giardini Prof. Dipartimento di Chimica, Università di Roma "La Sapienza", P.le Aldo Moro 5, CNR-IMIP, Via S. Loja, 85050 Tito, Roma, ItalySearch for more papers by this authorAlessandra Paladini Dr., Alessandra Paladini Dr. Dipartimento di Chimica, Università di Roma "La Sapienza", P.le Aldo Moro 5, CNR-IMIP, Via S. Loja, 85050 Tito, Roma, ItalySearch for more papers by this author Biagio Velino Dr., Biagio Velino Dr. Dipartimento di Chimica Fisica e Inorganica dell'Università, Viale Risorgimento 4, 40136 Bologna, ItalySearch for more papers by this authorPaolo Ottaviani Dr., Paolo Ottaviani Dr. Dipartimento di Chimica "G. Ciamician" dell' Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-2099456Search for more papers by this authorWalther Caminati Prof., Walther Caminati Prof. [email protected] Dipartimento di Chimica "G. Ciamician" dell' Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-2099456Search for more papers by this authorAnna Giardini Prof., Anna Giardini Prof. Dipartimento di Chimica, Università di Roma "La Sapienza", P.le Aldo Moro 5, CNR-IMIP, Via S. Loja, 85050 Tito, Roma, ItalySearch for more papers by this authorAlessandra Paladini Dr., Alessandra Paladini Dr. Dipartimento di Chimica, Università di Roma "La Sapienza", P.le Aldo Moro 5, CNR-IMIP, Via S. Loja, 85050 Tito, Roma, ItalySearch for more papers by this author First published: 03 March 2006 https://doi.org/10.1002/cphc.200500385Citations: 19Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Graphical Abstract Nonbonding interactions: The most stable configuration of indanole as determined by rotational spectroscopy in supersonic expansions results in the hydroxyl group in the equatorial position, with the hydroxyl hydrogen pointing towards the cyclopentenyl ring (see figure). Five other rotamers, generated by the hydroxyl group rotation and by the five-membered ring puckering, relax to this one upon supersonic expansion. Supporting Information Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2267/2006/z500385_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. References 1D. Consalvo, A. Van der Avoird, S. Piccirillo, M. Coreno, A. Giardini Guidoni, A. Mele, M. Snels, J. Chem. Phys. 1993, 99, 8398–8406. 10.1063/1.465615 CASWeb of Science®Google Scholar 2W. H. Pirkle, T. C. Pochapsky, Chem. Rev. 1989, 89, 327–338 10.1021/cr00092a006 Web of Science®Google Scholar 3E. Eliel, S. H. Wilen, N. L. Menden, Stereochemistry of Organic Compounds, Wiley-Interscience, New York, 1994 Google Scholar 4A. Latini, D. Toja, S. Piccirillo, A. Giardini Guidoni, M. Speranza, Angew. Chem. 1999, 111, 838–840; 10.1002/(SICI)1521-3757(19990315)111:6<838::AID-ANGE838>3.0.CO;2-O Google ScholarAngew. Chem. Int. Ed. 1999, 38, 815–817. 10.1002/(SICI)1521-3773(19990315)38:6<815::AID-ANIE815>3.0.CO;2-Z CASWeb of Science®Google Scholar 5D. Scuderi, A. Paladini, M. Satta, D. Catone, S. Piccirillo, M. Speranza, A. Giardini Guidoni, Phys. Chem. Chem. Phys. 2002, 4, 4999–5003. 10.1039/B204909K CASWeb of Science®Google Scholar 6Gaussian 03 Revision B.04, M. J. Frisch, G. W. Trucks, Gaussian Inc., Pittsburgh PA, 2003. Google Scholar 7W. Caminati, Phys. Chem. Chem. Phys. 2004, 6, 2806–2809. 10.1039/b315707e CASWeb of Science®Google Scholar 8R. Sanchez, W. Caminati, J. C. López, J. L. Alonso, Chem. Phys. Lett. 2005, 414, 226–229. 10.1016/j.cplett.2005.08.071 CASWeb of Science®Google Scholar 9J. K. G. Watson in Vibrational Spectra and Structure, Vol. 6 (Ed.: ), Elsevier, New York/Amsterdam, 1977, pp. 1–89. Google Scholar 10J. Kraitchman, Am. J. Phys. 1953, 21, 17–25. 10.1119/1.1933338 CASWeb of Science®Google Scholar 11R. S. Ruoff, T. D. Klots, T. Emilson, H. S. Gutowsky, J. Chem. Phys. 1990, 93, 3142–3150. 10.1063/1.458848 CASWeb of Science®Google Scholar 12S. Melandri, W. Caminati, L. B. Favero, A. Millemaggi, P. G. Favero, J. Mol. Struct. 1995, 352/353, 253–258. 10.1016/0022-2860(94)08516-K CASWeb of Science®Google Scholar 13S. Melandri, G. Maccaferri, A. Maris, A. Millemaggi, W. Caminati, P. G. Favero, Chem. Phys. Lett. 1996, 261, 267–271. 10.1016/0009-2614(96)00977-3 CASWeb of Science®Google Scholar Citing Literature Volume7, Issue3March 13, 2006Pages 565-568 ReferencesRelatedInformation

Angewandte Chemie International EditionVolume 45, Issue 15 p. 2438-2442 Communication Relative Strengths of the OH⋅⋅⋅Cl and OH⋅⋅⋅F Hydrogen Bonds† Walther Caminati Prof., Walther Caminati Prof. walther.caminati@unibo.it Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this authorSonia Melandri Dr., Sonia Melandri Dr. Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this authorAssimo Maris Dr., Assimo Maris Dr. Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this authorPaolo Ottaviani Dr., Paolo Ottaviani Dr. Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this author Walther Caminati Prof., Walther Caminati Prof. walther.caminati@unibo.it Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this authorSonia Melandri Dr., Sonia Melandri Dr. Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this authorAssimo Maris Dr., Assimo Maris Dr. Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this authorPaolo Ottaviani Dr., Paolo Ottaviani Dr. Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, 40126 Bologna, Italy, Fax: (+39) 051-209-9456Search for more papers by this author First published: 24 March 2006 https://doi.org/10.1002/anie.200504486Citations: 71 † We thank the Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR, PRIN 2004) and the University of Bologna (ex 60 % and funds for special topics) for financial support. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Which bond goes where? The observed conformer of H2O⋅⋅⋅ClFCH2 displays one OH⋅⋅⋅Cl and two weak CH⋅⋅⋅O hydrogen-bonding interactions. The dissociation energy of this conformer is estimated to be 8.5 kJ mol−1 from the centrifugal distortion effects. Citing Literature Supporting Information Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z504486_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume45, Issue15April 3, 2006Pages 2438-2442 RelatedInformation

The rotational spectrum of 1-benzofuran has been investigated by three different rotational spectroscopy techniques: (i) millimeterwave absorption free jet spectroscopy, useful for a fast assignment of the spectrum; (ii) molecular beam Fourier transform microwave spectroscopy, sensitive to detect less abundant isotopic species in natural abundance; (iii) waveguide conventional microwave spectroscopy, useful for the study of intramolecular dynamics, through the rotational spectra of the vibrational satellites of low energy modes. Besides the rotational spectrum of the ground state of the normal species, the spectra of 9 singly substituted C-13 and O-18 isotopomers in natural abundance, and of 6 vibrational satellites, have been measured. Precise structural parameters for the molecule, as well as information on the potential energy surface of the low energy vibrations, have been obtained. The dipole moment components have been determined to be mu(a) = 0.216 (2) and mu(b) = 0.720 (3) D, respectively.

The rotational spectrum of coumaran has been investigated by free-jet absorption millimeter-wave spectroscopy. All transitions are split into two component lines due to the low barrier to ring puckering of the five-membered ring. The ground state splitting (ΔE01=93682.02(2)MHz, 3.124895(1)cm−1) is much larger than the value inferred from the infrared spectrum [0.7cm−1, E. Bondoc, T. Klots, J. Laane, J. Phys. Chem. A 104 (2000) 275]. Such a discrepancy affects the estimate of the anomeric effect, as discussed in the text.

The molecular beam Fourier transform microwave spectrum of 1,4-dioxane-trifluoromethane has been assigned and measured. The two subunits form a cage stabilized by one C-H...O and two C-H...F weak hydrogen bonds. The C-H...O link involves the axial lone pair of one of the two equivalent ring oxygens, while the two C-H...F bridges connect trifluoromethane to the two axial hydrogens in positions 3 and 5. The dissociation energy has been estimated from the D(J) centrifugal distortion parameter to be approximately 6.8 kJ/mol.

The molecular beam Fourier transform microwave spectrum of cyclobutanone-trifluoromethane has been assigned and measured. The carbon atom of trifluoromethane lies in the plane of the heavy atoms of cyclobutanone. The complex is stabilized by one C-H...O=C and two C-H...F-C weak hydrogen bonds. The C-H...O=C interaction, involving one carbonylic oxygen, is studied for the first time in detail with rotationally resolved spectroscopy. The two C-H...F-C weak hydrogen bonds involve two fluorine atoms of trifluoromethane and two hydrogens of the same methylenic group in the alpha position.

The rotational spectrum of the molecular complex difluorodimethylsilane–argon has been investigated by pulsed jet absorption millimeter wave and pulsed supersonic jet Fourier transform microwave spectroscopy. The absolute energy minimum corresponds to a conformation with the argon atom lying in the F–Si–F plane of symmetry of difluorodimethylsilane. This is confirmed by the analysis of the observed splitting due to the internal rotation of two equivalent methyl groups. The V3 barrier to the internal rotation of the two methyl groups has been determined to be 4.857(5) kJ/mol. The distance of Ar from the center of mass of difluorodimethylsilane is 4.07 Å, with Ar–Si line forming an angle of 60.6° with the C–Si–C bisector. The zero point dissociation energy is estimated, from the centrifugal distortion constant DJ, to be 2.75 kJ/mol.

The 1:1 molecular complex between oxetane and water has been investigated by using free-jet millimeter-wave spectroscopy. The rotational spectra of five isotopomers (with H(2)O, D(2)O, DOH, HOD and H(2) (18)O) have been assigned. Partial r(0) and r(s) structures of the complex have been derived. The water moiety lies in the plane of symmetry of oxetane, with the "free" hydrogen E with respect to the ring. The oxetane ring appears to be slightly nonplanar, with the C(beta) carbon tilted on the opposite side of the water unity. The three atoms involved in the hydrogen bond adopt a linear arrangement with an O(ring).H distance of about 1.86 A, and the angle between the COC bisector and the O(ring).H bond being congruent with 106 degrees. Additionally, quantum-chemical calculations for the complex were performed and were found to be in agreement with the experimental results.

The rotational spectrum of the dimethyl ether-hydrogen fluoride complex was assigned by millimetre-wave free-jet absorption spectroscopy. Fine details of the spectrum were resolved by FT microwave molecular-beam spectroscopy. The HF group acts as a proton donor and tunnels at a rate of 44178.2(7) MHz between the two oxygen lone pairs, which corresponds to an inversion barrier of 0.17 (1) kcal mol-1. The barrier to internal rotation of the two methyl groups is about 25% lower relative to the isolated ether.

The ground-state rotational spectra of three isotopomers C4H4S...(HBr)-Br-79, C4H4S...(HBr)-Br-81 and C4H4S...(DBr)-Br-79 of a weakly bound complex formed by thiophene and hydrogen bromide have been observed in the gas phase by means of a pulsed-jet, Fourier-transform instrument. Each spectrum was analysed and fitted to give rotational constants A(0), B-0 and C-0, centrifugal distortion constants Delta(J), Delta(JK), Delta(K), delta(J) and delta(JK) and the components chi(aa), chi(bb) - chi(cc) and chi(ab) of the bromine nuclear quadrupole coupling tensor. A detailed analysis of the spectroscopic constants established that the geometry of the complex is of the face-on type. The Br atom of HBr is located close to the perpendicular drawn through the centre of mass of the thiophene ring and the H atom of HBr lies between the Br atom and the ring. The angle alpha(az) made by the HBr internuclear axis z with the a- axis has the two possible values +/- 9.83degrees. The preferred structure is that generated when the positive value of the angle is chosen and has the HBr sub-unit pointing in the direction of the S atom of thiophene. The determined geometrical parameters are r(S...H) = 2.728(3) Angstrom, phi = 116.0(2)degrees and theta = 7.08(4)degrees, where phi is the angle made by the S...H internuclear line with the local C-2 axis of thiophene and theta is the angular deviation of the S...H-Br nuclei from collinearity.

The rotational spectrum of 2,2′-biphenol has been investigated by millimeter wave absorption free jet spectroscopy. The two sides of the phenyl rings with attached the hydroxyl group form a dihedral angle of 112.7°. Each hydroxyl group is nearly co-planar to the ring to which it belongs, and points towards the π system of the adjacent ring.

In dimethylether–HCl, the HCl group is tunnelling between the two lone pairs of the ether oxygen at a rate of 8182(7) MHz, through a barrier of 69 cm−1, as deduced from the free jet millimetre wave absorption spectrum.

We have investigated the Raman profiles of the nu(C[Triple Bond]N) and nu(C=O) vibrational modes of the nematic liquid crystal ME6N (4-cyanophenyl-4(')-hexylbenzoate) in the isotropic phase at different temperatures and used them as probes of the dynamics and structural organization of this liquid. The vibrational time correlation functions of the nu(C[Triple Bond]N) mode, rather adequately interpreted within the assumption of exponential modulation function (the Kubo-Rothschild theory), indicate that the system experiences an intermediate dynamical regime that gets only slightly faster with increasing temperature. However, this theory fails in predicting the non-exponential behavior that the time correlation functions manifest in the long time range (t>3 ps). For this reason we have additionally approached the interpretation of vibrational correlation functions in terms of the theory formulated by Rothschild and co-workers for locally structured liquids. The application of this theory reveals that the molecular dynamics in this liquid crystal in the isotropic phase is that deriving from a distribution of differently sized clusters, which narrows as the temperature increases. Even at the highest temperature reached in this study (87 degrees C above the nematic-isotropic transition), the liquid has not yet achieved the structure of the simple liquid and the dynamics has not reached the limit of the single channel process. The vibrational and orientational relaxations occur in very different time scales. The temperature independence of the orientational dynamics in the whole range from 55 degrees C to 135 degrees C has been referred to the nonhydrodynamic behavior of the system, arising when local pseudonematic structures persist for times longer than the orientational relaxation. The occurrence of the process of resonant vibrational energy transfer between the C=O groups of adjacent molecules has been revealed in the isotropic phase by a slightly positive Raman noncoincidence effect in the band associated with the nu(C=O) mode. A qualitative interpretation is tentatively given in terms of partial cancellation of contributions deriving from structures having opposite orientations of their C=O groups.

The rotational spectrum of the molecular complex dimethylsilane-argon was investigated by free-jet absorption millimeter-wave and molecular-beam Fourier transform spectroscopy. The absolute energy minimum corresponds to a conformation in which the argon atom lies in the plane of symmetry of dimethylsilane, perpendicular to the C-Si-C plane. The distance of Ar atom is tilted 14 degrees away from the Si atom. The zero-point dissociation energy was estimated from the centrifugal distortion constant D(J) to be 2.2 kJ mol(-1). Small splitting, due to tunneling of the Ar atom and internal rotation of the two methyl groups, was observed, measured, and used to determine the potential energy surface for these motions.

The molecular beam Fourier transform microwave spectra of two isotopomers of the 1:1 complex between indole and water have been measured. The water molecule has been reliably located in the complex from these experimental data. The complex has a Cs symmetry with an N–H⋯O hydrogen bond and the plane of the H2O molecule perpendicular to the indole plane. The two-dimensional potential energy surface of the internal rotation and inversion of water in the complex, evaluated with B3LYP/6-31G** or MP2/6-31G** quantum chemical calculations, suggests the tunneling motion of water to take place with the contribute of both motions. The experimental evidence combined with flexible model calculations, indicate, however, that the tunneling motion is mainly an internal rotation of water around its C2 symmetry axis.

The ground-state rotational spectrum of the dimethyl ether dimer, (DME)(2), has been studied by molecular beam Fourier transform microwave and free jet millimeter wave absorption spectroscopies. The molecular beam Fourier transform microwave spectra of the (DME-d(6))(2), (DME-(13)C)(2), (DME-d(6))...(DME), (DME-(13)C)...(DME), and (DME)...(DME-(13)C) isotopomers have also been assigned. The rotational parameters have been interpreted in terms of a C(s) geometry with the two monomers bound by three weak C-H...O hydrogen bonds, each with an average interaction energy of about 1.9 kJ/mol. The experimental data combined with high-level ab initio calculations show this kind of interaction to be improper, blue-shifted hydrogen bonding, with an average shortening of the C-H bonds involved in the hydrogen bonding of 0.0014 A. The length of the C-H...O hydrogen bonds, r(O...H), is in the range 2.52-2.59 A.

The concentration dependence of the Raman noncoincidence effect (NCE) of the C-O and O-H stretching bands of methanol is investigated in methanol/CCl4 mixtures in the range of 1.0 greater than or equal to x(m greater than or equal to) 0.1, where x(m) is the mole fraction of methanol, by performing Raman spectroscopic measurements and molecular dynamics (MD) simulations. Band asymmetry observed for both bands is carefully taken into account. The experimental and simulation results are in satisfactory agreement with each other. For the C-O stretching band, it is observed that the magnitude of the negative NCE gets larger upon dilution in CCl4 down to x(m) similar to 0.2, contrary to the expectation of becoming smaller from simple guess that the NCE arises from intermolecular vibrational resonant interactions between methanol molecules, which, on average, get separated from each other upon dilution. For the O-H stretching band, the magnitude of the positive NCE remains almost the same upon dilution down to x(m) similar to 0.3. These apparently peculiar experimental results are reasonably explained by the MD simulations on the basis of the transition dipole coupling (TDC) mechanism of intermolecular resonant vibrational interactions and the simulated hydrogen-bonded liquid structures. In the case of the C-O stretching band, the negative NCE arises mainly from positive vibrational coupling between hydrogen-bonded pairs of molecules, which is partially canceled by negative vibrational coupling between molecules in different hydrogen-bonded chains. In the case of the O-H stretching band, the positive NCE arises predominantly from negative vibrational coupling within hydrogen-bonded chains. As a result, a locally anisotropic change in the liquid structure that occurs upon dilution, in which, around each molecule, intermolecular distances do not change very much along hydrogen-bond directions but do change significantly in other directions, gives rise to the apparently peculiar behavior of the NCE described above.

The free-jet millimeter-wave spectrum of the complex 2-pyridone⋯water has been measured. The water is strongly linked to the partner group through a double hydrogen bond. We could not observe the spectrum of 2-hydroxypyridine⋯water (2-hydroxypyridine is more abundant than 2-pyridone in the tautomeric mixture). This failure is explained by density functional and ab initio calculations on the relative stability of the two 1:1 complexes with water. Estimates of the dissociation energy have been obtained both from the centrifugal distortion effects and from quantum chemical calculations.