Synthesis and experimental study of through-space hydrogen-fluorine and carbon-fluorine spin-spin coupling in 4,5-substituted 1-acetyl-8-fluoronaphthalenes

The synthesis and NMR study (1H, 13C, and 19F) of a complete series of 4,5-substituted 1-acetyl-8-fluoronaphthalenes are reported. This data revealed a 6J(H,F) and a 5J(C,F) through space coupling between the fluorine and the methyl on the acetyl group (1H and 13C). The magnitude of this coupling constant changes depending on the nature of the substituent at C-4, the internuclear distance, and the solvent.     

Through-space spin-spin coupling in van der Waals dimers and CH/pi interacting systems. An ab initio and DFT study

The through-space J(HH) and J(CH) spin-spin coupling constants of model van der Waals dimers (involving methane, ethylene, and benzene), and of selected compounds showing the CH/pi interaction, have been investigated by means of DFT and ab initio calculations. In the range of intermolecular separations for which the interaction is stabilizing, weak couplings (0.1-0.3 Hz) are predicted for J(CH), while the corresponding J(HH) couplings are much smaller. The relative contributions (Fermi-contact, spin-orbit, and spin-dipole) are strongly dependent on the geometry of the dimers and on the distance; the non-negligible values of J(CH) for pi systems stem largely from an incomplete cancellation of spin-orbit terms. The results obtained for the larger molecules, that is, acetonitrile@calix[4]arene 5, the imine 6, and the aryl ester 7 are consistent with those on the model dimers. For 7, the occurrence of a through-space mechanism for the transmission of coupling is established by examining trends in the magnitude of couplings as a function of the number of intervening covalent bonds.     

Preparation of 4-aryl-1,2,3,4-tetrahydro-3,3-dimethylisoquinolines and 1,2,3,4-tetrahydro-3,3-dimethyl-4-phenylbenz[h]isoquinolines

Synthetic procedures to prepare a number of 4-aryl-1,2,3,4-tetrahydro-3,3-dimethylisoquinolines and their benzo-homogues 3 through a series of intermediates are described. The condensation of α-(1-amino-1-methylethyl)arylmethanols 5 with arylaldehydes 6 gave imino derivatives 7 which on reduction with borohydride gave secondary amines 8 . The treatment of 8 with mineral acids gave the target compounds 3 . Biological activities of 3 are briefly discussed.     

The effects of substituents on the 5J long-range spin-spin coupling constants in substituted benzaldehydes

Proton magnetic resonance spectra of several mono- and disubstituted benzaldehydes were studied using CW, INDOR and double resonance techniques. It was verified that substitution in the para position has no effect on the long-range coupling of the aldehydic proton with the ring protons five bonds away. Substitution in the ortho and meta positions (with the exception of 2,4-dinitrobenzaldehyde) follows closely the additivity rule effects of the substituents.     

"Through-space" nuclear spin-spin J(PP) coupling in tetraphosphine ferrocenyl derivatives: a (31)P NMR and X-ray structure correlation study for coordination complexes

Herein, we report on (31)P(31)P solution-phase "through-space" nuclear spin-spin coupling constants (J(PP)) from a novel family of organometallic tetraphosphine nickel and palladium complexes. These J(PP) constants were accurately determined through NMR iterative simulation based on the second-order spectra obtained for the compounds. The corresponding solid-state X-ray structures of the complexes were determined, and the "through-space" P.P distances are reported. Due to the blocked conformation of the species in solution, a qualitative and semiquantitative experimental correlation is obtained, which links the geometric parameters and the intensity of the corresponding P.P coupling constant. The lone-pair overlap theory developed for (19)F(19)F and (15)N(19)F "through-space" couplings in organic compounds [J. Am. Chem. Soc. 1973, 95, 7747-7752; 2000, 122, 4108-4116] appears to be a reliable foundation on which to account for our results. Based on the reported observations, the lone-pair overlap model is extended to "through-space" (31)P(31)P coupling, and the model is broadened to encompass metal orbital contributions for coordination complexes. Some of the predictions and consequences of the proposed theory are discussed.     

Long-range spin-spin coupling between protons and fluorine nuclei in trifluoroacetylpyrroles

Conclusions Long-range spin-spin coupling between the fluorine and H⁴ nuclei of the pyrrole ring is realized in the¹H and¹⁹F NMR spectra of 2-organyl-5-trifluoroacetylpyrroles and their N-vinyl derivatives. The predominant conformations of the molecules of the studied compounds were established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1122–1124, May, 1979.     

An experimental and theoretical study of spin-spin coupling in chlorosilanes

An experimental and theoretical study of the absolute value of the one-bond spin-spin coupling constant |(1)J(Si,H)| in SiH(n)Cl(4-n) (n = 0-4) dissolved in THF-d(8) is presented. We found |(1)J(Si,H)| to increase with an increasing number of chlorine substituents, and the quantitative changes were found to differ from the values previously reported for the same compounds dissolved in cyclohexane-d(12). We also report on the variations in |(1)J(Si,H)| as a function of temperature, which we found to be linearly temperature dependent for the chlorine-substituted silanes and temperature independent for SiH(4). Furthermore, the temperature dependence of |(1)J(Si,H)| varied between the different chlorosilanes. Solvent-solute interactions were studied by quantum chemical DFT calculations. The variations in chloro-silane bond lengths upon adduct formation and the different adduct interaction energies may explain the temperature dependences of the coupling constants.     

Vibrational spectra of 2-fluoro-5-nitro-, 2-fluoro-4-nitro-, 4-fluoro-2-nitro- and 5-fluoro-2-nitrotoluene

The mid- and far-IR absorption spectra of four substituted toluenes, namely 2-fluoro-5-nitro-, 2-fluoro-4-nitro-, 4-fluoro-2-nitro- and 5-fluoro-2-nitrotoluene were recorded. Vibrational assignments are proposed assuming C_s, symmetry for the molecules.     

NDDO MO calculations: isotropic hyperfine coupling constants and nuclear spin-spin coupling constants

The nonempirical NDDO MO method in its unrestricted form has been used to evaluate isotropic hyperfine coupling constants and nuclear spin-spin coupling constants. Satisfactory agreement with INDO and experimental results is obtained.     

Nuclear spin-spin coupling constants in a coupled-cluster polarization propagator approach

A recently derived coupled-cluster doubles polarization propagator approximation (CCDPPA) for excitation energies and transition moments is extended to the calculation of nuclear spin-spin coupling constants. As expected, in cases where the perturbation is small (e.g. C₂H₂) the difference between results obtained using the present scheme and results obtained using the perturbative second-order polarization propagator approach (SOPPA) is small (1-5%). However, for CH⁺ the difference is found to be more than 40%.     

13C-13C spin-spin coupling constants in 3-carene

Novosibirsk Institute of Organic Chemistry, Siberian Branch, USSR Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, Vol. 6, pp. 853–854, November–December, 1989.     

NMR spin-spin coupling constants in polymethine dyes as polarity indicators

Herein, we explore the use of spin-spin coupling constants (SSCCs) in merocyanine (MCYNE) dyes as indicators of polarity. For this purpose, we use Car-Parrinello hybrid quantum mechanics/molecular mechanics (QM/MM) to determine the structures of MCYNE in solvents of different polarity, followed by computations of the SSCCs by using QM/MM linear-response theory. The molecular geometry of MCYNE switches between neutral, cyanine-like, and zwitterionic depending on the polarity of the solvent. This structural variation is clearly reflected in the proton SSCCs in the polymethine backbone, which are highly sensitive to the dielectric nature of the environment; this mechanism can be used as a "polarity indicator" for different microenvironments. This result is highlighted by computing the SSCCs of the MCYNE probe in the cavity of the beta-lactoglobulin protein. The computed SSCCs clearly indicate a non-polar hydrophobic dielectric nature of this cavity.