The solid state 13C-NMR and 19F-NMR spectra of some graphite fluorides

The solid state ¹³C nuclear magnetic resonance spectra of fluorinated graphites show two resonances, one of which is assigned to aromatic carbon and the other to aliphatic carbon. The resonances are very broad with the high-field resonance centered at about 35 ppm below tetramethylsilane (TMS) and a low-field resonance centered at about 160 ppm below tetramethylsilane. The high-field resonance is typical of an sp³-like carbon and the low-field resonance is assigned to sp²-like carbons. It is found that the aromatic resonance in graphite decreases with an increase in fluorination of the graphite fluorides examined in this study. The ¹⁹F nuclear magnetic resonance spectra of C₄F and CF₁ each show one resonance. The fluorine resonance in C₄F is 180 ppm above CFCI₃ whereas the fluorine resonance in CF₁ is 55 ppm above CFCI₃. These peaks are in the range for fluorine bonded to aromatic and aliphatic carbons, respectively.     

29Si and 13C NMR spectra of chloro- and fluoro-substituted linear permethylpolysilanes

²⁹Si and ¹³C NMR spectra are reported for the three halopolysilane series Me(SiMe₂)_nCl, Cl(SiMe₂)_nCl and F(SiMe₂)_nF, where n = 2 to 6. Except for the dihalodisilanes (XSiMe₂)₂, data for all of the compounds fit linear relationships based on substituent constants for chlorine or fluorine atoms in the α, β and γ positions. The effects of halogen substitution on ²⁹Si and ¹³C chemical shifts are rapidly attenuated along the polysilane chain, becoming negligible four atoms away from the halogen. The NMR data provide no evidence for long-range electronic transmission from chlorine or fluorine in halopermethylpolysilanes of the type suggested by other workers [1].     

The 13C-NMR spectrum and stereochemistry of heteronemin

The ¹³C-NMR spectrum of heteronemin (1), a new sesterterpene from marine origin is reported. Assignment of most of the signals was accomplished by a combination of off-resonance decoupling, PRFT measurement, comparison with suitable known model compounds and LIS measurements. An all trand-anti-trans configuration is suggested from 1 according to the ¹³C-NMR data.     

Selective 1H-13C correlation by low power single frequency off-resonance decoupling assisted by exhaustive simulation techniques

Selectivity in the ¹H-¹³C correlation for assignments of ¹³C spectra is enhanced by recording single frequency off-resonance ¹³C NMR spectra with low decoupling field strength (? 2J_o), distortion of signal patterns is avoided by submitting the spin system to a previous noise broad band decoupling. Correlation is obtained by comparison of observed and simulated 2-D spectra (π ¹³C vs decoupler frequency) joined to fitting of the curve J_R = f (decoupler frequency) with the equation of Freeman and Anderson.₁     

1H,2H,19F and 31P NMR and ESR investigations of aryl-t-butyl nitroxides

Aspects of translocation of spin to fluorine and phosphorus are discussed. (2p–3d)_π overlap in phosphorus is insignificant. Spin polarization and (2p–3p)_π overlap are opposing spin transfer mechanisms for phosphorus. The³¹P NMR spectrum of the nitroxide from 7a shows some features which are not fully understood. Some gain in resolution of the NMR spectra can be achieved by deuteration, but it is considerably lower than predicted.     

13C-19F couplings and 19F NMR shifts of cycloalkyl,bicycloalkyl and steroid monofluoro compounds1

The stereospecifity of ¹³C-¹⁹F couplings is investigated with 20 alicyclic compounds. One bond couplings, ranging from 168 to 214 Hz, can be represented as a function of the corresponding ¹³C-H coupling constants. For comparison ¹³C-¹H couplings are determined for norboraane and adamantane and indicate considerable s character at the bridgehead C-H bond of the latter compound. One bond and geminal couplings (ranging from 18 to 24 Hz) are found to depend not significantly on the steric environment. With vicinal couplings a strong dependence is established on torsional angles, which is fitted to a Karplus function. Typical values for CCCF trans arrangements are around 10 Hz, for gauche angles less than 1.5 Hz. Vicinal couplings are substantially altered by electronegative substituents and by hybridization changes of participating carbon atoms. The ³J values observed with cycloalkylfluorides are interpreted on the basis of model geometries for the corresponding hydrocarbons. The influence of solvent and temperature changes is restricted to one bond couplings. ¹⁹F shifts in cyclohexane derivatives are constantly at higher field for axial fluorine (by ~20 ppm), but otherwise there is no significant relation to the orientation of neighbouring bonds, nor to ¹³C shifts of the Cα-F carbon atoms or to the corresponding one bond couplings.     

Nuclear magnetic 13C?19F double resonance: Fluorine broad band decoupling

The feasibility of broad band fluorine decoupling for ¹³C NMR spectroscopy, employing a new composite pulse sequence, is shown. The application of this sequence allows the decoupling of fluorine nuclei over almost the total range of chemical shifts in fluoroorganic compounds, at magnetic fields of up to 2.3 T, without extensive demands on the decoupler power amplifier. The range of expected chemical shifts of fluorine bonded to carbons is briefly discussed.     

13C- und 199Sn-NMR untersuchungen an alkinylstannanen

Chemical shifts δ(¹³C), δ(¹¹⁹Sn) and coupling constants J(¹¹⁹Sn¹³C) for alkynylstannanes of the type R_4-nSn(CCR′)_n (n = 1–4) are reported. The values of ¹J(¹¹⁹Sn¹³C) and ²J(¹¹⁹SnC¹³C) depend upon the nature of the substituent R′. ¹J(¹¹⁹Sn¹³C) in Sn(CCCH₃)₄ is 1168 Hz, much larger than a value predicted in the literature of ca. 700 Hz. The comparison of δ(¹¹⁹Sn) for (CH₃)₂Sn(CCR′)₂ and 1,1,4,4-tetramethyl-1-stannacyclohexadi-2,5-ene suggests that the δ(¹¹⁹Sn) of alkynylstannanes are determined only to a small extent by the diamagnetic anisotropic effect of the CC-triple bond.     

Investigation of sesquiterpene lactones by13C NMR spectroscopy. III.13C MNR spectra of artemin and its derivatives

The¹³C NMR spectra obtained under conditions of complete and incomplete decoupling from protons of the sesquiterpene lactone artemin (I), its dihydro derivative (II), and its acetyl derivative (III) have been studied. An assignment has been made of the chemical shifts of all the carbon atoms by comparison of the¹³C NMR spectra of (I), (II), and (III) with one another and also by comparison with literature information.V. L. Komarov Institute of Botany, Academy of Sciences of the AzSSR, Baku, Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 576–578, September–October, 1983.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

13C NMR investigations of the ferroelectric phase transition of tris-sarcosine calcium chloride

¹³C NMR spectra were measured for tris-sarcosine calcium chloride (TSCC) crystals in the paraelectric phase (at temperatures of ? 300 and 150 K) and in the ferroelectric phase (at temperatures of 119 K) by double-resonance techniques with proton decoupling. The ferroelastic single crystals were rotated around their three crystallographic axes to derive the tensors of magnetic shielding for the different carboxylic carbon atoms. There is no change of the eigenvalues and eigenvectors of the tensors at the phase transition. The results are consistent with the interpretation of former EPR data.     

15N and 17O NMR spectra of some nitrogen- and oxygen-containing polyfluoroaromatic compounds

The effect of substitution of hydrogen by fluorine on the ¹⁵N and ¹⁷O NMR chemical shifts in N-sulphinylarylamines, azoxy- benzenes, C,N-diarylnitrones and aromatic azomethines has been studied. Changes in nitrogen screening are controlled mainly by the radial factor <r^?3>_2p(N), which depends on the electron density on nitrogen, those in oxygen screening — by the two factors, the excitation energy ΔE^?1 and the radial factor <r^?3>_2p(0), which may operate in the same or opposite directions. The ¹⁵N and ¹⁷O NMR spectra of the above compounds did not show any specific effects of perfluorination.     

Fourier 13C NMR and PMR including 13C satellites of oriented cyanopropyne

Fourier ¹³C and proton NMR spectra of cyanopropyne partially oriented by a nematic phase have been recorded and interpreted. It is shown that more accurate measurements are obtained much more rapidly by observing ¹³C satellites by Fourier PMR than by direct observation of the ¹³C spectrum. The geometry has been extracted from direct couplings; a small but systematic discrepancy with microwave spectroscopy is observed for the carboncarbon bond lengths.     

13C-NMR studies of polyfluorinated hydrocarbons,carboxylic acid derivatives,alcohols and ethers

δ¹³C values and coupling constants (¹J(¹³C¹H), ¹J(¹³C¹³C), ⁿJ(¹⁹F¹³C) are reported for 19 polyfluorinated organic compounds. It is shown that the shielding of carbon depends upon the number of fluorine atoms in α -position. If the R_F-group is linked to a π -system hyperconjugative $\text{and}$ η-π interaction accounts for the δ¹³C data. The values ¹J(¹³C¹H) and ¹J(¹³C¹³C) are in qualitative agreement with changes of the s-character of the respective bonds.     

13C13C spin spin coupling constants in azulenes

[4-¹³C]- Azulene and [4-¹³C]-4-methylazulene have been synthesized. The ¹³C¹³C spin coupling constants have been measured and interpreted in terms of πMO theory.     

Treatment of Be+ ( 1 s? 1)2S Auger resonance with different decouplings of the dilated electron propagator

The diagonal 2ph-TDA and quasiparticle decouplings of the dilated electron propagator (based on an underlying bi-variational SCF) are utilized to calculate energy and width of the Be⁺(1_s ⁻¹)²S Auger resonance for the first time. Comparison with experimental and other theoretical results reveals that the renormalized infinite order diagonal 2ph-TDA decoupling seems to offer a less balanced approach to the treatment of resonances than the second-order decoupling. The diagonal quasiparticle approximation to the self energy is seen to offer an effective and economic alternative to the non-diagonal propagator calculations.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

Vibrational energy transfer between 12C16O and 13C16O

The rate of the energy exchange process ¹²C¹⁶O (v= 1)+ ¹³C¹⁶O (v= 0) ? ¹²C¹⁶O (v= 0) +¹³C¹⁶O (v= 1) + 47.2 cm^?1 has been measured by laser-induced fluorescence, k₂ = (7.2 ± 0.3) × 10⁴ s^?1 Torr^?1 at 293 K. This result is in reasonable agreement with that predicted by theories based on long-range dipole-dipole interactions     

Determination of fluorine in geological materials by fast neutron activation based on the 19F(n,2n)18F reaction

The determination of fluorine in geological materials by fast neutron activation analysis based on the ¹⁹F(n, 2n)¹⁸F reaction is described. Fast neutrons are produced by irradiation of a thick beryllium target with 14.5 MeV deuerons. A rotating smple holder allows simultaneous irradiation of samples and standards. Fluorine-18 is separated by steam distillation of hexafluorosilicic acid or by extraction with triphenylatimony(V) dichloride and the annihilation radiation is measured with γ—γ coincidence equipment. The nuclear interference of recoil protons that induce the ¹⁸O(p,n)¹⁸F reaction is evaluated by means of synthetic samples: for a rock containing 43.4% of oxygen and 0.5% of hydrogen, the interference corresponds to 4.4 μg g^?1 fluorine. The method was applied to USGS and NIMROC reference rocks: for concentrations between 6000 and 50 μg g^?1, the relative standard deviation ranged from 2 to 10%.     

14N and 13C NMR of tautomeric systems of hydroxy-pyridines

¹⁴N NMR is shown to be an efficient method of investigation of the tautomeric equilibria in hydroxy-and related substituted pyridines. Large relative ¹⁴N chemical shifts within tautomeric pairs estimated from N-Me and O-Me derivatives make possible quantitative determinations of the equilibria. Qualitative conclusions may be drawn from ¹⁴N line widths as well as from ¹³C and proton chemical shifts.