1H-,13C- und19F-NMR-Untersuchungen zur Struktur der intramolekularen Wasserstoffbindung in dencis-Enolen von 2-Trifluoracetylcycloalkanonen (original) (raw)
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Monatshefte f�r Chemie Chemical Monthly, 1991
The 1H, 13C and 19FNMR spectra of some 2-trifluoroacetylcycloalkanones comprising five-, six-, seven-, and eight-membered ring systems have been studied. These systems have been shown by 19FNMR spectroscopy to be over 90% enolized. The effects of ring size on the 1H, 13C and 19F chemical shifts and 13C-19F coupling constants are discussed. The direction of enolization in these systems was investigated by 1H, ~3C and 19F NMR spectroscopy and evidences were presented in favour of a dominant exocyclic enol form in the five-and an endocyclic enol form in the six-, seven-and eight-membered ring systems.
The journal of physical chemistry. B, 2007
Theoretical studies are performed on enflurane (CHFCl-CF(2)-O-CHF(2)) to investigate the conformational properties and vibrational spectra. Calculations are carried out at the B3LYP/6-31G(d) level along with a natural bond orbital (NBO) analysis. Experimental infrared spectra are investigated in carbon tetrachloride solution at room temperature and in argon matrix at 12 K. In agreement with previously reported data (Pfeiffer, A.; Mack, H.-G.; Oberhammer, H. J. Am. Chem. Soc. 1998, 120, 6384), it is shown that the four most stable conformers possess a trans configuration of the C-C-O-C skeleton and a gauche orientation of the CHF(2) group (with respect to the central C-O bond). These conformations are favored by electrostatic interaction between the H atom of the CHF(2) group and the F atoms of the central CF(2) group. Hyperconjugation effects from the O lone pairs to the antibonding orbitals of the neighboring C-H and C-F bonds also contribute to the stability of the four conformers...
The Journal of Organic Chemistry, 2008
Low-temperature NMR spectra show that the title compound exists as a pair of conformational enantiomers, generated by the restricted rotation about the C9-Pr i bond, the corresponding interconversion barrier being 6.9 kcal mol -1 . This interpretation is supported by theoretical (MM and DFT) calculations and by the experimental determination of the analogous barriers occurring in the related MeCdO and Bu t CdO derivatives.
Journal of Molecular Structure, 1993
The Raman spectrum (4000-200 cm −1) of liquid and infrared spectra (4000-400 cm −1) of gaseous and liquid 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane, c-OSi(CH 3) 2 CH 2 CH 2 Si(CH 3) 2 , have been recorded. Ab initio and density functional theory (DFT) calculations with several different basis sets including diffuse functions have been carried out to predict the conformational stabilities with comparisons to disiloxane (H 3 SiOSiH 3)and 2,5-disila-1-oxacyclopentane (c-OSiH 2 CH 2 CH 2 SiH 2). These calculations predict the twisted C 2 conformer as the most stable form of the ring compounds, with the planar C 2v conformer a transition state and the envelope C s conformer not a stable form. These predicted stabilities are supported by the vibrational data. Additionally, force constants, infrared intensities, Raman activities, depolarization ratios and scaled vibrational wavenumbers have been determined from MP2(full)/6-31G(d) calculations for all three molecules and compared with experimental values when available. Predicted r 0 structural parameters have been obtained for dimethyl ether, methyl silyl ether and disiloxane, which are compared with the experimentally determined values. On the basis of these data, estimated r 0 parameters are provided for both five-membered rings with the expectation that these values are as accurate as could be measured experimentally in the gas phase. The results are discussed and compared with corresponding quantities for some similar molecules.
Characterization of monofluorinated polycyclic aromatic compounds by1H,13C and19F NMR spectroscopy
Magnetic Resonance in Chemistry, 2005
Monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) have attracted much attention in analytical, environmental, toxicological and mechanistic studies because of their physico-chemical properties, which are closely similar to those of the parent PAHs. Because of this, full NMR characterization has become of interest. Complete 1 H, 13 C and 19 F NMR chemical shifts, and also 1 J(H,C), n J(C,F), n J(H,F) and n J(H,H) coupling constants, have been assigned for the F-PAHs 1-fluoronaphthalene, 2-fluorofluorene, 5fluoroacenaphthylene, 2-fluorophenanthrene, 3-fluorophenanthrene, 3-fluorofluoranthene, 1-fluoropyrene, 1fluorochrysene, 2-fluorochrysene, 3-fluorochrysene and 9-fluorobenzo[k]fluoranthene. To allow comparison with the corresponding parent PAHs, the 1 H and 13 C chemical shifts of acenaphthylene, phenanthrene, fluoranthene, pyrene and benzo[k]fluoranthene were determined. Chemical shift increments and the effects on the coupling constants from the fluorine substitution are discussed.
The Journal of organic chemistry, 2015
The synthesis of a series of α-trifluoromethylcyclohexanols and analogous trimethylsilyl ethers by addition of the Ruppert-Prakash reagent to substituted cyclohexanones is presented. A method for the assignment of configuration of such compounds, of related α-trifluoromethylcyclohexylamines and of quaternary trifluoromethyl-substituted carbons is described based on the determination of the (3)J(CH) coupling constant between the fluorine-decoupled (13)CF3 resonance and the vicinal hydrogens. This method is dubbed fluorine-decoupled carbon spectroscopy and abbreviated FDCS. The method is also applied to the configurational assignment of substances bearing mono-, di-, and perfluoroalkyl rather than trifluoromethyl groups. The configuration of all substances was verified by either (19)F-(1)H heteronuclear Overhauser spectroscopy (HOESY) or X-ray crystallography. The relative merits of FDCS and HOESY are compared and contrasted. (2)J(CH), (3)J(CH), and (4)J(CH) coupling constants to (19)...