苯对N,N-二甲基甲酰胺化合物1H NMR的影响研究

本文研究了N,N-二甲基甲酰胺(DMF)在四氯化碳和苯混合溶剂中的¹H NMR。观察到N,N-二甲基甲酰胺(DMF)分子中两个甲基和混合溶剂中苯的共振吸收峰的化学位移随苯的摩尔分数增加而逐渐移向高场,而且两个甲基共振吸收峰向高场移动的程度不同,α甲基较β甲基为甚。DMF分子中两个甲基和混合溶剂中苯的化学位移可以用线性方程表示(δ=A+Bx),这里x是混合溶剂中苯的摩尔分数。相关系数R接近于-1。     

Chemical shift referencing in MAS solid state NMR

Solid state 13C magic angle spinning (MAS) NMR spectra are typically referenced externally using a probe which does not incorporate a field frequency lock. Solution NMR shifts on the other hand are more often determined with respect to an internal reference and using a deuterium based field frequency lock. Further differences arise in solution NMR of proteins and nucleic acids where both 13C and 1H shifts are referenced by recording the frequency of the 1H resonance of DSS (sodium salt of 2,2-dimethyl-2-silapentane-5-sulphonic acid) instead of TMS (tetramethylsilane). In this note we investigate the difficulties in relating shifts measured relative to TMS and DSS by these various approaches in solution and solids NMR, and calibrate adamantane as an external 13C standard for solids NMR. We find that external chemical shift referencing of magic angle spinning spectra is typically quite reproducible and accurate, with better than +/-0.03 ppm accuracy being straight forward to achieve. Solid state and liquid phase NMR shifts obtained by magic angle spinning with external referencing agree with those measured using typical solution NMR hardware with the sample tube aligned with the applied field as long as magnetic susceptibility corrections and solvent shifts are taken into account. The DSS and TMS reference scales for 13C and 1H are related accurately using MAS NMR. Large solvent shifts for the 13C resonance in TMS in either deuterochloroform or methanol are observed, being +0.71 ppm and -0.74 ppm from external TMS, respectively. The ratio of the 13C resonance frequencies for the two carbons in solid adamantane to the 1H resonance of TMS is reported.     

Validity and Accuracy of Resonance Shift Prediction Formulas for Microcantilevers: A Review and Comparative Study

This article provides a review of methods of predicting mass-induced resonance shifts in microcantilevers. It combines a review of factors that influence resonance frequency shifts, such as material properties, size effects, and support compliance with a comparative study of accuracy of predicting resonance shifts due to mass adsorption. The applicability and accuracy of widely used formulas to correlate mass addition with resonance shift are assessed through comprehensive comparison with experimental measurements and numerical methods. The methods include both distributed parameter and lumped parameter formulations. The applications include distributed added masses, tip masses, and added mass at arbitrary locations along a cantilever span.     

2,2-二(甲硫基)乙烯基苯基酮1H NMR溶剂效应的研究

在四氯化碳介质中考察了苯对标题化合物的核磁共振谱的溶剂效应.观察到标题化合物分子中的两个甲硫基和混合溶剂中的苯的共振吸收峰随着苯的摩尔分数增加而逐渐移向高场,而且两个甲硫基向高场移动程度不同,ASIS值也随苯的摩尔分数增加而增加,得到了所有化学位移值和ASIS值与苯的摩尔分数呈线性关系,尝试用溶剂化作用解释了标题化合物的ASIS效应.     

1,1-二甲硫基-[1]-烯基丙二酸二甲酯与苯相互作用的1H NMR研究

本文在四氯化碳介质中考察了苯对1,1-二甲硫基-[1]-烯基丙二酸二甲酯的溶剂效应,观察到标题化合物分子内的甲基和溶剂苯的化学位移随着苯的摩尔分数增加而逐渐移向高场,溶剂苯的共振吸收峰是一个尖锐的单峰,同时发现了标题化合物分子中甲基和溶剂苯的化学位移值与混合溶剂苯的摩尔分数呈线性关系.     

1,1-二甲硫基—[1]—烯基丙二酸二甲酯与苯相互作用的~1H NMR研究

本文在四氯化碳介质中考察了苯对1,1-二甲硫基-[1]-烯基丙二酸二甲酯的溶剂效应,观察到标题化合物分子内的甲基和溶剂苯的化学位移随着苯的摩尔分数增加而逐渐移向高场,溶剂苯的共振吸收峰是一个尖锐的单峰,同时发现了标题化合物分子中甲基和溶剂苯的化学位移值与混合溶剂苯的摩尔分数呈线性关系.     

Improvements and New Evaluation of NIM4 Caesium Fountain Clock at NIM in 2005-2006

The NIM4 caesium fountain clock has been operating stably and sub-continually since August 2003. We present our improvements on NIM4 in 2005-06 and the most recent evaluation for its frequency shifts with an uncertainty of 5 × 10^-15. A 203-day comparison between NIM4 and GPS time shows an agreement of 2 × 10^-14. Finally the construction of the NIM5 transportable caesium fountain clock is briefly reported.     

Further conventions for NMR shielding and chemical shifts IUPAC recommendations 2008

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the ¹H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS).

This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating ¹³C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.     

GIAO/DFT calculations of relative conformer energies and 1H NMR shifts of unsaturated alcohols in benzene

Density functional theory calculations were performed on alkenols and alkynols at the PBE1PBE/6‐311 + G(d,p) level with the inclusion of solvent (benzene) effects by the integral‐equation‐formalism polarizable continuum model (IEFPCM). For the smaller molecules, conformers in which the OH group is in the vicinity of the double or triple bond are preferred, but this preference falls as the alkyl chain is lengthened. The solvent effect on the relative Gibbs energies of different conformers is irregular, and in only two cases, 3‐buten‐1‐ol and 3‐butyn‐1‐ol, is there marked levelling. Gauge‐including atomic orbital calculations, based on the PBE1PBE/6‐311 + G(d,p) geometries but using a larger basis set, cc‐pVTZ, give nuclear magnetic resonance shifts for all the protons in each conformer. Overall shifts are calculated by weighing these according to the conformer population. Calculated values are well correlated with experimental data from high‐dilution spectra in the same solvent, ranging from about 0.4 to 5.8 ppm, with a slope of 1.09 ± 0.01. Calculations on some alcohols with hetero‐atom substituents confirm that these also prefer gauche (synclinal) conformers in the gas phase, with a less marked preference in benzene. The nuclear magnetic resonance shifts, however, are calculated to be on average over 0.8 ppm higher than observed. Copyright © 2011 John Wiley & Sons, Ltd.     

On the possibility of new resonances in multiphoton processes

The principle of a generalized resonance mechanism is proposed.. It is deduced from new resonances which are expected to be observed in any multiphoton process. The example of four-photon ionization of atomic caesium is considered.     

Medium effects on the fluorine chemical shifts of non-polar molecules in liquids

The gas-to-infinite dilution fluorine chemical shifts of CF₄, SiF₄, SF₆, C₆F₆, p-fluorotoluene and p-difluorobenzene have been measured for a series of non-polar solvents. Downfield displacements ranging from 3–16 p.p.m. have been observed. Comparisons with proton solvent shifts make it evident that the London dispersion forces are the principal agent in causing the shifts. However, unlike proton resonance where the local diamagnetic shielding is mostly affected, it is probably through the local paramagnetic shielding that solvents alter fluorine chemical shifts.     

High pressure behaviour of liquid caesium

This paper deals with the anomalous behaviour of liquid caesium at high pressures. A model for the phenomenon of electron collapse in the liquid phase, based on the anomalous density variation of liquid caesium with pressure has been proposed. The process of 6s→5d electron collapse is pictured as the formation of a virtual bound state and the tunnelling process accounts for the 6s⇌5d dynamic conversion. The same model together with the Friedel sum rule has been used to explain the resistivity variation of liquid caesium with pressure. The resistivity minimum observed in most of the liquid alkali metals in the low pressure region has been explained. The agreement with the experimental curve is good in the low pressure region whereas a large discrepancy exists at higher pressures. This may be due to the breakdown of the Ziman’s resistivity formula under conditions of resonance scattering.     

丙酮肟1H核磁共振溶剂效应的研究

测定了丙酮肟在四氯化碳、氯仿、二氯甲烷、苯和甲苯溶剂中随丙酮肟摩尔浓度变化的¹H NMR谱,观察到在氯代甲烷溶剂中,丙酮肟分子中两个甲基和氯代甲烷的质子共振峰随丙同肟摩尔浓度增加而逐渐移向高场,而羟基共振峰却逐渐移向低场。其两个甲基表现为单峰。在芳烃溶剂中,丙酮肟分子中两个甲基和芳烃质子共振峰随丙酮肟摩尔浓度增加逐渐移向低场,且两个甲基表现为双峰,得到了所有化学位移与丙酮肟摩尔浓度呈线性关系。     

Detection of B-FSK signals using schmidt trigger

Possibility to record B-FSK signals with use of stochastic resonance is studied. A Schmidt trigger is employed as bistable stochastic resonator. A digital model of the detector is proposed and quantitative results are obtained by means of simulations. Dependence of the probability of correctly detected bits on the added noise power and on the low-pass filter cutoff frequency is studied. Also the stability of the detector with respect to channel-introduced phase shifts is revealed.     

Nuclear Magnetic Resonance Studies in Gases

There are several reasons why nuclear magnetic resonance (NMR) studies in gases are important. At low pressures the interactions in the gas phase are essentially governed by two body collisions. It is therefore possible to study the intermolecular forces between two molecules approaching one another during collision from their influence on the chemical shifts of the nuclei of the molecules under considerations. The experimental measurements allow one to learn how the chemical shift is perturbed because of the presence of other molecules. This knowledge can then be transferred to interpret solvent effects in condensed phases and for detection of any solvent-solute interactions in such systems.     

Meerwein酯与苯相互作用的1H NMR研究

测定了Meerwein酯(1,3,5,7,-四羧甲基二环[3,3,1]壬-2,6-二烯-2,6-二醇)在四氯化碳和苯混合溶剂中随苯的摩尔分数变化的¹H NMR谱.观察到分子中两类不同的甲基的化学位移随苯的摩尔分数增加都逐渐移向高场,分子中不同位置上的甲基的化学位移向高场移动程度不同,原处低场的甲基的δ比原处高场甲基的δ要大,两条吸收峰在苯的摩尔数渐增时先是重合后又渐渐分开,所有化学位移可以用线性方程δ=A+BX表示.     

Comments on np elastic scattering, 142–800 MeV

Important new data of McNaughton et al. on np Wolfenstein parameters are added to NN phase-shift analysis. At 800 MeV, there is a dramatic improvement and one can see with confidence which way phase shifts are heading from 500 to 800 MeV. Dispersive effects in ³D₁ and ³G₃ herald the onset of I = 0 inelasticity. Phase shifts account naturally for the energy dependence of Δσ_L and Δσ_T for np scattering and do not support the claim of Beddo et al. for an I = 0 dibaryon resonance near 733 MeV.     

Nucleon-nucleon potentials including πNΔ coupling effects

We show that in the nonrelativistic limit the two-pion exchange contribution to the nucleon-nucleon (NN) interaction can be well approximated by the twice iterated static pion-exchange potentials that couple the NN channel with the NΔ (1236 resonance) and ΔΔ channels. A phenomenological short (ω-meson) range potential is added to the pion-exchange potentials to study the NN phase shifts and the deuteron properties. The S- and P- state phase shifts can be well explained in this model with a very reasonable short-range interaction. The Δ-percentage in the deuteron is found to be ≈ 0.6%. Probably because of the nonrelativistic approximations, the D-state phase shifts at E_lab > 100 MeV are not too well reproduced.     

Experimental investigation of slow light propagation in degenerate two-level system

Slowing a light pulse in a degenerate two-level system is observed with a double-frequency sweeping technique. The effects of coupling beam intensity, cell temperature and frequency detunings of the coupling and probe beams in resonance, on the slowing of light propagation in such a system are investigated. It is found that group velocities depend strongly on polarization combinations. A group velocity $v_{\rm g}$=6760m/s of light pulses in caesium vapour is obtained under the optimal parameters.