19F and 1H NMR and ESR investigations of aryl-t-butyl nitroxides and nitronylnitroxides

¹H and ¹⁹F NMR and ESR spectra of several nitroxides have been recorded. The ¹⁹F couplings are sensitive to steric factors and this shows why the simple linear relationship a_F = O_eff^F· ?_C^π is not adequate. The π and σ spin delocalization mechanisms are demonstrated. The spin transmission via oxygen and sulphur is affected by geometry (efficiency of pπ-nπ overlap), pπ-dπ overlap only plays a role in positively charged S atoms (sulphones). The absolute sign of the proton coupling in an alkyl chain depends upon chain length and substituents. The syntheses of several stable nitroxides are described.     

Myosin-catalyzed ATP hydrolysis elucidated by 31P NMR kinetic studies and 1H PFG-diffusion measurements

We conducted ³¹P NMR kinetic studies and ¹H-diffusion measurements on myosin-catalyzed hydrolysis of adenosine triphosphate (ATP) under varied conditions. The data elucidate well the overall hydrolysis rate and various factors that significantly impact the reaction. We found that the enzymatic hydrolysis of ATP to adenosine diphosphate (ADP) was followed by ADP hydrolysis, and different nucleotides such as ADP and guanosine triphosphate acted as competitors of ATP. Increasing ATP or Mg²⁺ concentration resulted in decreased hydrolysis rate, and such effect can be related to the decrease of ATP diffusion constants. Below 50 °C, the hydrolysis was accelerated by increasing temperature following the Arrhenius’ law, but the hydrolysis rate was significantly lowered at higher temperature (~60 °C), due to the thermal–denaturation of myosin. The optimal pH range was around pH 6–8. These results are important for characterization of myosin-catalyzed ATP hydrolysis, and the method is also applicable to other enzymatic nucleotide reactions.     

31P, 19F and 1H NMR spectroscopic study of the reaction of bis(trifluoromethyl)phosphine and solid KOH. Synthesis of the phosphaalkene CF3PCF2

The formation and subsequent reaction of the phosphaalkene CF₃PCF₂ obtained via dehydrofluorination of (CF₃)₂PH with KOH pellets at room temperature has been studied by multinuclear NMR spectroscopy.     

Effects of external electric fields on 1H, 19F,and 14N NMR spectra of 2, 4, 6-trifluoronitrobenzene

When a polar liquid is subjected to an electric field, the dipoles obtain a small average orientation. At sufficiently high field strengths direct spin—spin dipolar and quadrUpolar electric field interactions may modify the NMR spetrum.NMR electric field experiments are reported for the proton, fluorine, and nitrogen NMR spectra of neat 2, 4, 6-trifluoronitrobenzene. The observed alignment values are smaller than those predicted on the basis of Onsager's theory.The ¹⁴N quadrupole coupling constant as been deduced from a comparison of the qUadrupolar and dipolar electric field effects.An upper limit of the absolute value of the anisotropy of the para-¹⁹F chemical shift has been inferred from the absence of a detectable displacement of the resonance on application of an electric field.     

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.     

15N and 31P NMR spectroscopy of triclorophosphazopolyfluoroaryls.

¹⁵N and ³¹P NMR spectra of trichlorophosphazopolyfluoroaryls obtained by the interaction between polyfluoroanilines and PCI₅ in benzene (Kirsanov reaction) have been investigated. The interconversions of monomeric and dimeric forms of trichlorophosphazopolyfluoroaryls by ³¹P NMR are also shown.     

基于竞争配位的Ca2+特异性响应1H/19F磁共振成像分子探针

合成了一种含~(19)F的Mn~(2+)配合物3,12-二(2-氧代-2-((2,2,2-三氟乙基)氨基)乙基)-6,9-二氧杂-3,12-二氮杂十四烷酸锰(Ⅱ)(Mn(Ⅱ)-L,1),可实现对Ca~(2+)特异响应的~1H/~(19)F磁共振成像分析。~(19)F核在近距离的顺磁性Mn~(2+)影响下产生了顺磁弛豫增强作用,使~(19)F的横向弛豫时间T_2急剧缩短而磁共振信号锐减。当有Ca~(2+)存在时,与配体L的竞争配位使得~(19)F远离Mn~(2+)离子,从而~(19)F磁共振信号得到恢复。同时,由于Mn~(2+)离子从配合态变为游离态,水配位数增加使得其对~1H的纵向弛豫时间T_1弛豫性能增加,从而~1H磁共振成像信号也增强。相关实验的结果证实了该配合物是一种能对Ca~(2+)特异性响应的~1H/~(19)F磁共振成像探针。     

1H和19F NMR研究镍系催化丁二烯聚合中醇类对BF3·Oet2的增溶作用

The solubility of BF₃OEt₂ in hydrogenated gasoline was improved greatly by means of premixing BF₃OEt₂ with C₃H₁₇OH in nickel catalyst system, so that the effeciency of fluorine in the system was increased markedly. It is confirmed that there was a intermolecular hydrogen bond between alcohol and BF₃OEt₂ molecules by using ¹H NMR, which was a vital factor to lead the solubilization of BF₃OEt₂ in hydrogenated gasoline. Otherwise, the caculation formula of the chemical shift ofproton in hydroxy, ¹H = xipi,was suggested in hydrogen bond system.     

Trioxaphosphocanes-1,3,6,2, etude par R.M.N. (13C, 1H, 31P et stereochimie

The stereochemistry of several 2-R-1,3,6,2-trioxaphosphocanes (R = Cl, OCH₃, CH₃, N(CH₃)₃ has been investigated by ¹H, ¹³C and ³¹P n m r spectroscopy.     

19F NMR chemical shifts of n-F-alkyl compounds

The examination of ¹⁹F chemical shifts for ca. 650 F-alkylated compounds of general formula CF₃(CF₂)_nCF₂X led to the following conclusions: the CF₂ groups α to X are very sensitive to the nature of X, and are spread over a range of 85 ppm. The effect of the length of the F-alkyl chain decreases rapidly, so that δCF₂(α) can already be considered as characteristic of X for n = 1 or 2 for most practical purposes. Solvent effects (in 9 different solvents having ε = 1.8 to 52.1) were found to be rather small except for the F-alkyl iodides. A chart which indicates the domain in which the CF₂(α) resonance signal is to be expected is given for 42 different series of F-alkylated compounds; it is expected to provide the synthetic chemist with a useful tool for the identification and characterization of such compounds.     

Influence of the phosphine ligands in the 1H and 31P NMR behaviour of [(η3-allyl)Py(phophine)Cl] complexes

The ¹H and ³¹P NMR spectra of (η³-allyl)Pt(PR₃)Cl] (PR₃ = PMe₃, PCy₃, P-t-Bu₃, P-n-Bu₃, PPh₃, PPh₂Me, PPhMe₂ and P(p-Tol)₃) complexes in chloroform have been studied. The results suggest that there is bonding interaction between the phosphine and the allyl group via central metal atom.     

31P MAS NMR固体核磁共振研究稀土改性Y分子筛的酸性

以三甲基磷氧（TMPO）和三丁基磷氧（TBPO）为探针分子,用³¹P魔角旋转核磁共振（³¹P MAS NMR）法对稀土改性Y型分子筛的酸性进行了定性和定量分析. 结果表明,以TMPO为探针分子的³¹P MAS NMR谱分别在δ = 78,70,65,62,58,55和53处存在与酸中心相关的吸收峰,其中δ = 78和70处吸收峰与分子筛内部和外部酸性有关,δ = 65,62,58和53处吸收峰归属于TMPO在分子筛内部Brönsted酸中心上的贡献,δ = 55处吸收峰归属于TMPO在分子筛内部Lewis酸中心上的贡献. 随着稀土含量的增加,中等强度Brönsted酸中心（δ = 62和58）数量显著增加,而强Brönsted酸中心（δ = 65）和较弱Lewis酸中心（δ = 55）数量显著降低. 结合分子筛骨架铝和非骨架铝对分子筛酸性的影响进一步探讨了稀土改型Y分子筛的酸性.     

The protonation constants and 31P NMR of tetra-, penta-, hexa- and heptapolyphospates

The first and second protonation constants of linear polyphosphates at 25°C and ionic strength 0.1 have been evaluated: log K₁ = 8.91, log K₁₂ = 6.13 for P₂O₇^4?(P₂); log K₁ = 8.88, log K₁₂ = 5.86 for P₃O₁₀^5?(P₃); log K₁ = 8.40, log K₁₂ = 6.58 for P₄O₁₃^6?(P₄); log K₁ = 8.15, log K₁₂ = 7.03 for P₅O₁₆^7?(P₅); log K₁ = 8.12, log K₁₂ = 7.16 for P₆O₁₉^8?(P₆); log K₁ = 8.07, log K₁₂ = 7.18 for P₇O₂₂^9?(P₇). The variations of these values with the polyphosphate chain length have been discussed. A simple identification for polyphosphate species utilizing ¹³P NMR signal ratio of middle to end P has been proposed. By applying a micro ion-exchange technique, a rapid concentration of each polyphosphate and the subsequent preparation of the magnesium salt have been accomplished.     

19F shielding anisotropies of 2,4,6-trifluoronitrobenzene from nematic phase NMR

The customary assumption in nematic phase NMR of axial symmetry of the chemical shift tensor along the chemical bond has been shown to be unwarranted for the fluorine shielding tensor in 2,4,6-trifluoronitrobenzene.     

Stereochemical studies of 2-hydroxychromanones by 1H NMR spectroscopy

2-Hydroxychromanones (2a–2f) were synthesized by ring closing of 2-hydroxyacetophenones (1a, b) and 2-hyroxypropiophenones (1c–1f). In the case of 2-hydroxy-3-methyl-chromanones (2c–2f) a mixture of cis and trans isomers was obtained. The trans isomers are conformalionally homogeneous, the cis isomers exist in a conformational equilibrium. At room temperature the isomers are transformed into each other via opening of the heteroring. This process becomes faster in alkaline medium and the β-diketo form 4 can also be observed.     

Study of reversible proton transfer from 2,2,2-trifluoronitroethane to amines by dynamic1H and19F NMR

The interaction between the weak CH-acid CF₃CH₂NO₂ and aliphatic amines has been studied by NMR in CDCl₃ and CFCl₃ solutions. It is shown that no measurable amounts of H-bonded complexes are formed. However, reversible proton transfer with the formation of ion pairs takes place. The kinetic parameters of this process have been determined.

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CH- CF₃CH₂NO₂ CDCl₃ CFCl₃. , , . .

     

NMR (1H, 13C, 29Si) study of some allylhalogenosilanes

¹H, ¹³C and ²⁹Si NMR spectra of the allylchlorosilanes (CH₂CH-CH₂-)_xSiCl_4?x and of triallylbromosilane have been analysed. Results are discussed in terms of inductive and steric effects and of contributions of diamagnetic anisotropy. There is no conclusive evidence for (p-d)π conjugation.     

Trends in 19F-19F and 29Si-19F coupling constants in organosilicon derivatives containing SiF2 and Si2F4 units

Consideration of ¹⁹F-¹⁹F and ²⁹Si-¹⁹F coupling constants in a series of organosilicon derivatives containing SiF₂ and Si₂F₄ units reveals a number of trends which are useful for structural and stereochemical assignments. For example the vicinal ¹⁹F-¹⁹F coupling constants in a number of CSiF₂SiF₂C- derivatives (including straight chain compounds, disilacyclobutanes and disilacyclohexanes) show an apparent linear dependence on dihedral angle, varying in magnitude from near zero for small values of φ up to ca. 19 Hz for φ ～ 180°. This is particularly useful for stereochemical assignments [1,2]. In addition ²⁹Si-¹⁹F coupling constants appear to fall in quite distinct ranges (¹J_SiF > 300 Hz, 29 Hz < ²J_SiF < 55 Hz, ³J_SiF < 10 Hz). This is quite useful for structural assignments [1,6]. Reaction of SiF₂ with 1,3-cyclohexadiene gives two new silicon fluorine compounds: a disilabicyclo[2,2,2]octene and an HSi₂F₅-substituted cyclohexadiene.