Temperature dependence of the chemical shifts of commonly employed proton n.m.r. reference compounds

The temperature dependence of the chemical shifts of ten commonly employed ¹H n.m.r. reference compounds of interest to both organic and biological workers was determined using the temperature independent standard ethane at low density. The water soluble standards sodium 2,2-dimethyl-2-silapentane-5-sulfonate and sodium 3-trimethylsilylpropionate-d₆ exhibited very small chemical shift changes over the range of 20–65 °C. Outside of this temperature interval the chemical shift is distinctly nonlinear, but still is sufficiently small to be neglected for many n.m.r. studies. In contrast, the temperature dependence of seven neat organic liquid reference standards was observed to be linear over a significant temperature range with slopes varying between 0.0009 and 0.0023 ppm °C^?1. Only tetramethylammonium chloride (in ²H₂O) exhibited a small but pronounced nonlinear temperature dependence over the full range investigated.     

Perfluororganozink-verbindungen: darstellung und eigenschaften von (Rf)2Zn-komplexen (Rf = CF3, C2F5, C3F7, C6F5) [1]

A new method for the preparation of bis(perfluoroorgano) zinc compounds is described: CF₃I and C₆F₅I react with dialkylzinc in the presence of a Lewis base quantitatively to give (CF₃)₂Zn and (C₆F₅)₂Zn complexes, while the analogous reactions with C₂F₅I and iC₃F₇I do not yield the pure compounds. ¹H, ¹⁹F n.m.r, i.r. and Raman spectra are presented.     

The structure of 1,2-dithioles studied by 13C n.m.r. spectroscopy

The charge separation between the dithiole ring and oxygen in 3-(1′,2′-dithiole-3′-ylidene)-6-methyl-2,3-dihydropyran-2,4-diones and 3-(1′,2′-dithiole-3′-ylidene)-2,3-dihydrobenzo[b] pyran-2,4-diones has been determined by ¹³C and ¹⁹F n.m.r. spectroscopy. By both methods it is found that these compounds are relatively polar. A correlation is established between the ¹³C chemical shift of some carbon atoms and the S2p binding energies measured by e.s.c.a. in the 1,2-dithiole derivatives. This correlation shows that these ¹³C shifts depend on the positive charge taken by the 1,2-dithiole ring and can then constitute a convenient evaluation of this charge.     

Bonding information in tungsten(VI) compounds from directly bonded fluorine and fluorophenoxy subtituents

The series of compounds (FC₆H₄O)_nWF_6-n, where n = 1-6 and F is meta or para to oxygen, has been prepared and all fluorine nmr chemical shifts determined. The W-$\text{F}$, para-$\text{F}$, and meta-$\text{F}$ resonances all shift upfield as a function of n with approximate relative sensitivities of 1, 1/20, and 1/30, respectively. All chemical shifts are also found to be sensitive to molecular stereochemistry, with subtituents trans to oxygen shifted to higher field than those trans to fluorine. ¹⁹F data is also reported for the complete series (C₆H₅O)_nWF_6-n     

A survey of wave function effects on theoretical calculation of gas phase F NMR chemical shifts using factorial design

The wave functions for calculating gas phase ¹⁹F chemical shifts were optimally selected using the factorial design as a multivariate technique. The effects of electron correlation, triple-ξ valance shell, diffuse function, and polarization function on calculated ¹⁹F chemical shifts were discussed. It is shown that of the four factors, electron correlation and the polarization functions affect the results significantly. B3LYP/6-31 + G(df,p) wave functions have been proposed as the best and the most efficient level of theory for calculating ¹⁹F chemical shifts. An additional series of fluoro compounds were used as a test set and their predicted ¹⁹F chemical shifts values confirmed the validity of the approaches.     

Primary Studies on Variation in Position of Trifluoromethyl Groups in Several Aromatic Group‐14 Derivatives by 19F‐NMR Spectroscopy

Variation in the position of CF₃ groups in several aromatic Group‐14 compounds was studied by ¹⁹F‐NMR spectroscopy. In these compounds R_nECl_4?n (n=1 or 2; E=Si, Ge, or Sn; R=2,4,6‐(CF₃)₃C₆H₂ (=Ar), 2,6‐(CF₃)₂C₆H₃ (=Ar′), or 2,4‐(CF₃)₂C₆H₃ (=Ar″)), Ar, Ar′, and Ar″ are all bulky, strongly electron‐withdrawing ligands. The ¹⁹F‐NMR studies of the variation in position of the CF₃ substituents in these compounds as revealed by chemical shifts could be correlated with the electronegativities of the central elements E, and with intramolecular E–F interactions derived from single‐crystal X‐ray diffraction data. These interactions are considered to play an important role in the stabilization of these compounds.     

Chemical shifts of F19 NMR in spectra of trifluorovinyl compounds

The regularities of the changes of the chemical shift in the F¹⁹ NMR of trifluorovinyl compounds are discussed in this paper. It has been shown that the conditions , where _F ⁰ is the shift of F¹⁹ in tetrafluorethylene (X=F) are satisfied for the chemical shifts of fluorine in compounds. An increase in the electronegativity of X leads to a decrease in the ionic nature of the C-F₃ bond and to a shift toward weak fields. The effect of X on the and shifts is not linked in a specific way to the electronegativity of the X group and is probably determined by the effect of the electric fields on the shielding of the F¹⁹ nucleus. Increments were calculated from the data obtained on the shifts in trifluorovinyl compounds. The method of increments was used for the assignment of the lines in 1, 2-difluoro olefins. This method for the assignment is confirmed by known data. Several cases for the application of the increment method are proposed. The results of spectral measurements of the F¹⁹ NMR in some trifluorovinyl compounds are given in the experimental part.     

A raman,infra-red and n.m.r. spectroscopic study of the pentafluorotellurate(IV) ion

The Raman, and infra-red spectra of Na⁺, K⁺, Rb⁺, Cs⁺, NH₄⁺, C₅H₅NH⁺ and $\text{n}$-Bu₄N⁺ salts of the TeF₅^- ion are reported. They are assigned C_s symmetry. ¹⁹F n.m.r. spectra of the $\text{n}$-Bu₄N⁺ salt show J(F_ax-F_eq)50.4Hz, J(¹⁹F_eq-¹²⁵Te)1375.7Hz, J(¹⁹F_ax-¹²⁵Te)2883.3Hz and J(¹⁹F_eq-¹²³Te)1143.8Hz. No n.m.r. evidence was found for TeF₆^2-.     

NMR studies on some monothio-β-diketonate complexes and the corresponding β-diketones containing a perfluoropropyl group

The ¹³C and ¹⁹F NMR spectra of nine metal complexes containing a monothio- β-diketone ligand with a perfluoropropyl group have been recorded in chloroform-d. The chelates are of the type (MRCSCHCOC₃F₇)_n where M is nickel, palladium and cobalt and n is 2 (Ni, Pd) and 3 (Co). The R- substituent is 2′-thienyl (C₄H₃S), phenyl (C₆H₅) or 2′-naphthyl (C₁₀H₇). Correlations between the chemical shifts of the complexes' and ligands' respective carbon and fluorine resonances are presented. The data shows a metal dependence on the diketonate carbon ring resonances when the R- substituent is kept constant. Correlations in the chemical shift data of the β-diketone carbon rosonances are also present. ¹⁹F noise decoupled ¹³C NMR spectral data, ¹³C{¹⁹}, assisted in assigning the perfluoropropyl carbon resonances.     

The reactions of 1-hydroxy-halogenopropanes with fluorinating agents

1-Hydroxy-2-bromopropane and the corresponding 2-iodo compounds react readily with (1,1,2-trifluoro-2-chloroethyl) diethylamine to give the rearranged 1-halogeno-2-fluoro derivatives, whereas 1-hydroxy-2-chloropropane under the same conditions affords the direct substitution product, 1-fluoro-2-chloropropane. 1-Hydroxy-2-bromopropane reacts readily with anhydrous HF to give exclusively the rearranged fluoro compound. The ¹⁹F n.m.r. data of these compounds are reported and the mechanism of the rearrangement discussed.     

Cyclisierung neuer Trimethylsilylalkylaminohalogensilane

Cyclisation of New Trimethylsilylalkylaminohalosilanes Compounds of the composition RSiCl₂NR′SiMe₃ (R = Cl, CH₃, C₂H₅, C₆H₅; R′ = CH₃, C₂H₅, C(CH₃)₃) are obtained by the reaction of silicon halides with the lithium salts of silylamines. Under suitable experimental conditions the reaction leads to the formation of the corresponding Si? N four- and six-membered ring systems (RSiHalNR′)_n (Hal = F, Cl; n = 2 or 3) under elimination of trimethylhalosilane. The i.r., mass, ³⁵Cl-n.q.r., ¹H and ¹⁹F-n.m.r. spectra of these compounds are reported.     

NMR Studies of the Structures of Cyclic Phosphorus Compounds

Abstract

[RNPOCl]₃ (R = Ph, p-Tol, p-MeOC₆H₄) has been shown by ³¹P n.m.r. to consist mainly of the 2α, 4α, 6β(C₂) isomer (AB₂ spin system), along with small amounts of the symmetric (C₃) isomer (2α, 4α, 6α). The ³¹P shifts are almost independent of the nature of the group R. Confirmation of the ring structure requires the determination of J_BB which is achieved by second-order analysis of ¹³C or ¹H spectra. Similar techniques have been applied to the phosphorus-oxygen ring system [PhPO₂]₃. We have discovered a relationship between the orientation of N-phenyl substituents on cyclophosphazane ring systems and the ¹³C n.m.r. shifts of the ring carbons. In cyclodiphosphazanes the phenyl rings are coplanar with the P-N ring, whereas in cyclotriphosphazanes the phenyl rings are perpendicular to the P-N-P plane; the ¹³C shifts of the ortho and para carbons are quite different in these two situations, and we have used these shifts to obtain structural information on a number of cyclophosphazanes. Rotation of the ring about the C-N bond has also been studied by low-temperature n.m.r.     

Vinylierung und 91Zr-NMR-Spektren von Substituierten Zirconocendichloriden

Vinylation and ⁹¹Zr N.M.R. Spectra of substituted Zirconocene Dichlorides Substituted zirconocene dichlorides react with vinyl lithium with formation of zirconacyclopent-2-enes, Cp₂ZrCH = CHCH₂CH₂, or zirconocene butadiene complexes, Cp₂Zr(C₄H₆). The compounds obtained were characterized by their ¹H and ¹³C n.m.r. spectra. The ⁹¹Zr n.m.r. chemical shifts of substituted zirconocene dichlorides correlate with the bond angles Cp′? Zr? Cp′ and Cl? Zr? Cl respectively. They can be used to estimate the reaction behaviour of zirconocene dichlorides.     

The bonding situation in 1,3,2‐diazaphospholene derivatives as studied by solid‐state NMR spectroscopy

The ³¹P chemical shift (CS) tensors of the 1,3,2‐diazaphospholenium cation 1 and the P‐chloro‐1,3,2‐diazaphospholenes 2 and 3 and the ³¹P and ¹⁹F CS tensors of the P‐fluoro‐1,3,2‐diazaphospholene 4 were characterized by solid‐state ³¹P and ¹⁹F NMR studies and quantum chemical model calculations. The computed orientation of the principal axes system of the ³¹P and ¹⁹F CS tensors in the P‐fluoro compound was found to be in good agreement with experimentally derived values obtained from evaluation of P–F dipolar interactions. A comparison of the trends in the chemical shifts of 1 – 4 with further available literature data confirms that the unique high shielding of δ₁₁ in the cation 1 can be related to the effective π‐conjugation in the five‐membered heterocycle, and that a further systematic decrease in δ₁₁ for the P‐halogen derivatives 2 – 4 is attributable to the increased perturbation of the π‐electron distribution by interaction with the halide donor. Copyright © 2002 John Wiley & Sons, Ltd.     

Salze von Halogenophosphorsäuren. XV. Sulfan-α,ω-diyl-bis(fluorodithiophosphate), Reaktionsprodukte des Fluoridabbaus schwefelreicher Phosphorsulfide

Salts of Halogenophosphoric Acids. XV. Sulfane-α,ω-diyl-bis(fluorodithiophosphates). Products of the Fluoride Degradation of Sulfur-rich Phosphorus Sulfides By the reaction of sulfur-rich phosphorus sulfides ?P₄S_10+m”? (m = 0,5 to 6) with fluorides MF (M = Na, K, NH₄) in acetonitrile or 1,2-dimethoxy-ethane mixtures of sulfane-α,ω-diyl-bis(fluorodithiophosphates) [(PFS₂)₂S_n]^2? (n = 1 to 8) are formed. The average chain length n of the sulfane derivatives depends on the S:P ratio of the starting phosphorus sulfides. The compounds are identified by ¹⁹F and ³¹P n.m.r. spectroscopy.     

Tieftemperatur-flüssigphase-fluorierung von (C6F5)2Te: Bildung von (C6F5)2TeF2, (C6F5)2TeF4 und (C6F11)2TeF4 [1]

(C₆F₅)₂Te reacts with elemental fluorine step by step to form the tellurium fluorides (C₆F₅)₂TeF₂, (C₆F₅)₂TeF₄ and (C₆F₁₁)₂TeF₄, which can be isolated in pure states. The intermediates (C₆F_11?2n)₂TeF₄ (n = 1,2) are detected spectroscopically. (C₆F₅)₂TeF₂ is also formed from the reaction of (C₆F₅)₂Te with XeF₂. The preparations, properties and ¹⁹F n.m.r. spectra of these new compounds are discussed, the mass and vibrational spectra are described.     

New unsymmetrical difluoroaromatic compounds and estimation of their reactivities in nucleophilic substitution

A series of previously unknown unsymmetrical difluoroaromatic compounds, viz., p-fluorobenzoylphenyl(p-fluorophenyl)-substituted imidazoles, pyrazines, and quinoxalines, were synthesized according to multistep procedures with the use of chloral as the key compound. The reactivities of the resulting difluoroaromatic compounds were estimated based on ¹⁹F and ¹³C NMR spectral data and the results of quantum-chemical calculations. The calculated charge densities on the C_ipso atoms correlate linearly with the experimental chemical shifts in the ¹⁹F and ¹³C NMR spectra. Difluoroaromatic compounds, which are characterized by _F > –110 and _C > 163 and by the charge density on the C_ipso atom higher than 0.08 e, are sufficiently activated to be used for the preparation of high-molecular-weight polyethers.     

Temperature effects on 13C n.m.r. chemical shifts of normal alkanes and some line r and branched 1-alkenes

¹³C n.m.r. chemical shifts of a number of 1,1-disubstituted ethylenes are presented. Moreover, effects of changing temperatures on the ¹³C n.m.r. chemical shifts of some of these compounds as well as of three normal alkanes are given. These variations in chemical shifts are attributed to varying amounts of sterically induced shifts in the different conformational equilibria. In addition to the well-known 1,4 interaction between two alkyl groups shielding effects on the carbon atoms of the connecting bonds are also proposed. No definite explanation of this effect is presented at this time. It is further shown that no simple correlations exist between ¹³C n.m.r. chemical shifts and calculated total charge densities at this level. Instead, the experimental results in 1-alkenes are rationalized by assuming a linear dependence of the ¹³C n.m.r. chemical shifts of C-1 and C-2 via rehybridizations on changes in bond angles for small skeletal deformations caused by steric interactions. These changes in geometries, as well as conformational energies in three 1-alkenes, were calculated by means of VFF calculations. Finally. upfield shifts for both C-2 and C-4 are proposed for those conformations of 1-alkenes in which the C-3? C-4 group interacts with the p_z-orbital of C-2.     

Darstellung fluorsilylsubstituierter Hydrazine

Preparation of Fluorosilylsubstituted Hydrazines Fluorosilanes of the type RSiF₃ and RR′SiF₂ (R = CH₃, s-C₄H₉, t-C₄H₉, C₆H₅; R′= CH₃, t-C₄H₉) react with lithium salts of N, N′-trimethylsilyl-phenyl-hydrazine and N, N′-bis- (trimethylsilyl)-hydrazine in a molar ratio 1:1 under formation of fluorosilylsubstituted hydrazines and LiF. The i.r., mass, ¹H and ¹⁹F n.m.r. spectra of the above mentioned compounds are reported.     

19F Chemical shift tensor in fluorobenzene compounds

Fluorine-19 NMR multiple-pulse experiments have been applied to a series of meta-, para- and ortho-substituted fluorobenzene compounds in the solid state. The principal elements of the ¹⁹F chemical shift tensor (σ₁₁, σ₂₂, σ< ₃₃) were determined and the orientation of the tensor axes was inferrred from secondary information like molecular motion, related compounds and liquid crystal studies. Comparison with anisotropies obtained from molecules dissolved in liquid crystals in the nematic phase is discussed where data are available. Using the Gicrke-Flygarc approach we were able to exctract the spin-rotation interaction tensor elements C_??, C_tcy;tcy; and C_zz of ¹⁹F in sever; fluorobenzene compounds.