1,720,976 research outputs found
Monomer Raman-Spectra of Mono- and Diols in the 3700 to 3560 Wavenumber Range
No full textProvided are the Raman-jet spectra in the region of 3700 to 3560 cm-1 for the following systems: 0-Cl1 (3-chloropropane-1,2-diol), 0-Br1 (3-bromopropane-1,2-diol), 1-phenyl-cis-cyclohexane-1,2-diol (c6-6Ph), ttBuMeOH (tri-tert-butyl-methanol), 1-Cl (1-chloropropan-2-ol), 2-Cl (2-chloropropan-1-ol), 1-Br (1-bromopropan-2-ol) and 2-Br (2-bromopropan-1-ol)
Dimer Raman-Spectra of Diols and tri-tert-Butylmethanol
No full textProvided are the Raman-jet spectra in the fundamental OH-stretching frequency region (ca. 3700 to 3250 cm-1) for the following systems: ethane-1,2-diol (0-0), propane-1,2-diol (0-M), butane-2,3-diol (M-M), 2-methyl-propane-1,2-diol (0-MM), pinacol (MM-MM), 3-butene-1,2-diol (0-V), trans-cyclopentane-1,2-diol (t5-5), trans-cyclohexane-1,2-diol (t6-6), trans-cycloheptane-1,2-diol (t7-7) and tri-tert-butylmethanol (ttBuMeOH).
Besides dimers, higher oligomers may also be present. In some instances both racemic and enantiopure spectra have been recorded.</p
xyz Structure Files of Diols
No full textWe provide the xyz structure files at the B3LYP-D3(BJ,abc)/ma-def2-TZVP level of computation for the following diols: ethane-1,2-diol (0-0), propane-1,2-diol (0-M), rac-butane-2,3-diol (rM-M), 2-methyl-propane-1,2-diol (0-MM), 2-methyl-butane-2,3-diol (M-MM), pinacol (MM-MM), 3-butene-1,2-diol (0-V), 1-phenyl-ethane-1,2-diol (0-Ph), trans-cyclobutane-1,2-diol (t4-4), trans-cyclopentane-1,2-diol (t5-5), trans-cyclohexane-1,2-diol (t6-6), trans-cycloheptane-1,2-diol (t7-7), cis-cyclohexane-1,2-diol (c6-6), 1-(1-hydroxy-1-methylethyl)-cyclopentanol (CP-MM) and [1,1'-bicyclopentyl]-1,1'-diol (CP-CP)
Predicted and experimental rotational constants as well as predicted xyz structure files of bromo- and chloropropanols
No full textWe provide predicted and experimental rotational constants as well as predicted xyz structure files of bromo- and chloropropanols. The experimental rotational fits can be found in the corresponding fits folder and always end with _form.out. A file labeled 1_35Cl_g_primeG_form.out, for example, corresponds to the g'G conformer of 1-chloropropan-2-ol for the 35Cl isotope with all other isotopes being present in their naturally most abundant forms.
The nomenclature used here is related to that of a previous study (T. Goldstein, M. Snow, B. Howard, “Intramolecular hydrogen bonding in chiral alcohols: The microwave spectrum of the chloropropanols”, J. Mol. Spectrosc. 2006, 236, 1–10, DOI: 10.1016/j.jms.2005.11.010) in the following way: 2-gG'/g-ga, 2-g'G/g'-gg for 2-X-propan-1-ols and 1-gG'/m-ga, 1-g'G/h-gg for 1-X-propan-2-ols (X = Cl, Br)
The xyz-files provided have been computed at the DF-CCSD(T)-F12a/VDZ-F12 level of theory. DF implies the use of density fitting. For bromine atoms, the VDZ-PP-F12 basis set was used instead.
A comparison of experimental rotational, quartic distortion and nuclear quadrupole coupling constants to computed ones can be found in Microwave_Br_Overview.xlsx and Microwave_Cl_Overview.xlsx. The distortion constants have been computed using Vibrational Perturbation Theory of Second Order (VPT2). B0_Overview.xlsx provides a comparison of computed equilibrium (Be), vibrational averaged rotational (B0), and vibrational averaged rotational constants including rotational distortion effects (B0 + dist). The B0 values have also been obtained with VPT2.</p
Raw microwave cavity data for bromo- and chloropropanols
No full textWe provide the raw cavity spectra recorded with the QCUMBER microwave spectrometer of the Obenchain group in Göttingen. The measurements include spectra for bromopropanol (mixture of 1-bromopropan-2-ol and 2-bromopropan-1-ol) and chloropropanol (mixture of 1-chloropropan-2-ol and 2-chloropropan-1-ol).
The filenames follow the convention: Leading digits of the center frequency_Decimal Place of the center frequency_Number of averagesavgs.dat. For example, 10621_780_322avgs.dat corresponds to a center frequency of 10621.780 MHz with a total of 322 spectra being averaged.
All data from the cavity experiment was collected using the FTMW++ program of Jens-Uwe Grabow. The program can be downloaded and installed freely on a Windows PC without any instrumentation. For a copy of the program you can contact the authors or contact Jens Grabow [email protected]. See Melanie Schnell, Deike Banser, Jens-Uwe Grabow; "Coaxially aligned electrodes for Stark-effect applied in resonators using a supersonic jet Fourier transform microwave spectrometer" Rev. Sci. Instrum. 2004; 75 (6): 2111–2115. DOI: 10.1063/1.1755439 for details on the program. </p
Monomer Raman-Jet Spectra of Diols in the 3700 to 3560 Wavenumber Range
No full textWe provide the Raman-jet spectra in the region of 3700 to 3560 cm-1 for the following diols: ethane-1,2-diol (0-0), propane-1,2-diol (0-M), rac-butane-2,3-diol (rM-M), 2-methyl-propane-1,2-diol (0-MM), 2-methyl-butane-2,3-diol (M-MM), pinacol (MM-MM), 3-butene-1,2-diol (0-V), 1-phenyl-ethane-1,2-diol (0-Ph), trans-cyclobutane-1,2-diol (t4-4), trans-cyclopentane-1,2-diol (t5-5), trans-cyclohexane-1,2-diol (t6-6), trans-cycloheptane-1,2-diol (t7-7), cis-cyclohexane-1,2-diol (c6-6), 1-(1-hydroxy-1-methylethyl)-cyclopentanol (CP-MM) and [1,1'-bicyclopentyl]-1,1'-diol (CP-CP)
Subtle hydrogen bonds: benchmarking with OH stretching fundamentals of vicinal diols in the gas phase
No full textThe theoretical description of spectral signatures for weakly bound hydrogen contacts between alcohol groups is challenging and remains poorly characterised. By combining Raman jet spectroscopy with appropriately scaled harmonic DFT predictions and relaxation path analyses for 16 vicinal diols (ethylene glycol (ethane-1,2-diol), propane-1,2-diol, 3,3,3-trifluoro-propane-1,2-diol, rac-butane-2,3-diol, 2-methyl-propane-1,2-diol, 2-methyl-butane-2,3-diol, pinacol (2,3-dimethyl-butane-2,3-diol), 3-butene-1,2-diol, 1-phenyl-ethane-1,2-diol, trans-cyclobutane-1,2-diol, trans-cyclopentane-1,2-diol, trans-cyclohexane-1,2-diol, trans-cycloheptane-1,2-diol, cis-cyclohexane-1,2-diol, 1-(1-hydroxy-1-methylethyl)-cyclopentanol and [1,1′-bicyclopentyl]-1,1′-diol), 69 conformational assignments become possible in a two-tier approach with a 5 diol training and an 11 diol test set. The latter reveals systematic deviations for ring strain and secondary π interactions, but otherwise a remarkably robust correction and correlation model based on hybrid DFT with a minimally augmented triple-zeta basis set is obtained, whereas GGA functionals perform significantly worse. Raw experimental data in the 3560–3700 cm−1 wavenumber range as well as computed geometries of all conformations invite further vibrational and structural benchmarking at the onset of hydrogen bonding. Beyond this diol-probed threshold, the accurate prediction of hydrogen bond induced shifts of different magnitudes remains one of the challenges for DFT functionals
Dispersion forces in chirality recognition – a density functional and wave function theory study of diols
No full textWe analyse how dispersion interactions impact chirality recognition, both in the structure and energy of diol clusters.In the discussion of chirality recognition, steric considerations and strongly directed interactions such as hydrogen bonds are primarily discussed. However, given the sheer size of biomolecules, it is expected that dispersion forces could also play a determining role for aggregate formation and associated chirality recognition. With the example of diol molecules, we explore different factors in the formation of homo- and hetero-dimers as well as their relative stability. By comparing density functional results with the analysis of local correlation methods, we infer the impact of dispersion not only on the energies but also on the structures of such chiral aggregates. A local orbital based scheme is used to calculate wave function dispersion-free gradients and compare to uncorrected density functional structures
Weak hydrogen bonding to halogens and chirality communication in propanols: Raman and microwave spectroscopy benchmark theory
No full textRaman and rotational spectroscopy allow us to benchmark different properties with theory and indirectly helps understanding chirality recognition. A possible correlation between OH stretching frequencies and the asymmetry parameter η is explored.Constitutional and conformational isomers of bromopropanol are vibrationally and rotationally characterised with parallels drawn to the structural chlorine analogues. A previous microwave spectroscopic study of the chloropropanols is re-examined and all systems are explored by Raman jet spectroscopy. For bromine, the entire nuclear quadrupole coupling tensors are accurately determined and compared to their chlorine counterparts. Tensor asymmetry parameters are determined and linked with the hydrogen bond strength as indicated by the downshift of the OH-stretching frequency. The spectroscopic constants derived from the observed transitions are used as benchmarks for a large variety of electronic structure methods followed by harmonic and anharmonic rovibrational treatments. The CCSD(T) electronic structure calculations provide the best performance, in particular once anharmonic and relativistic corrections are applied or implied. Standard DFT approaches vary substantially with respect to their systematic error cancellation across the investigated species, and cost-effective compromises for the different observables are proposed.Raman and rotational spectroscopy allow us to benchmark different properties with theory and indirectly helps understanding chirality recognition. A possible correlation between OH stretching frequencies and the asymmetry parameter η is explored.Constitutional and conformational isomers of bromopropanol are vibrationally and rotationally characterised with parallels drawn to the structural chlorine analogues. A previous microwave spectroscopic study of the chloropropanols is re-examined and all systems are explored by Raman jet spectroscopy. For bromine, the entire nuclear quadrupole coupling tensors are accurately determined and compared to their chlorine counterparts. Tensor asymmetry parameters are determined and linked with the hydrogen bond strength as indicated by the downshift of the OH-stretching frequency. The spectroscopic constants derived from the observed transitions are used as benchmarks for a large variety of electronic structure methods followed by harmonic and anharmonic rovibrational treatments. The CCSD(T) electronic structure calculations provide the best performance, in particular once anharmonic and relativistic corrections are applied or implied. Standard DFT approaches vary substantially with respect to their systematic error cancellation across the investigated species, and cost-effective compromises for the different observables are proposed.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Hydrogen‐Atom Tunneling in a Homochiral Environment
Full text linkThe role-exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans-1,2-cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation-inversion symmetry breaks down. This intriguing contrast in hydrogen-atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics
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