Shifts Of Organic Compounds Research Articles

When soils become sediments: Large-scale storage of soils in sandpits and lakes and the impact of reduction kinetics on heavy metals and arsenic release to groundwater

Simulating the storage of aerobic soils under water, the chemical speciation of heavy metals and arsenic was studied over a long-term reduction period. Time-dynamic and redox-discrete measurements in reactors were used to study geochemical changes. Large kinetic differences in the net-complexation quantities of heavy metals with sulfides was observed, and elevated pore water concentrations remained for a prolonged period (>1 year) specifically for As, B, Ba, Co, Mo, and Ni. Arsenic is associated to the iron phases as a co-precipitate or sorbed fraction to Fe-(hydr)oxides, and it is being released into solution as a consequence of the reduction of iron. The composition of dissolved organic matter (DOM) in reducing pore water was monitored, and relative contributions of fulvic, humic and hydrophylic compounds were measured via analytical batch procedures. Quantitative and qualitative shifts in organic compounds occur during reduction; DOM increased up to a factor 10, while fulvic acids become dominant over humic acids which disappear altogether as reduction progresses. Both the hydrophobic and hydrophilic fractions increase and may even become the dominant fraction.Reactive amorphous and crystalline iron phases, as well as dissolved FeII/FeIII speciation, were measured and used as input for the geochemical model to improve predictions for risk assessment to suboxic and anaerobic environments. The release of arsenic is related to readily reducible iron fractions that may be identified by 1 mM CaCl2 extraction procedure. Including DOM concentration shifts and compositional changes during reduction significantly improved model simulations, enabling the prediction of peak concentrations and identification of soils with increased emission risk. Practical methods are suggested to facilitate the practice of environmentally acceptable soil storage under water.

Redshift and Blueshift Due to Interaction between C–H Bond of Methyl Radicals and Highly Electronegative Oxygen

Conventional chemical shifts in organic compounds usually consist of a redshift; however, hybrid-type SiOC films were found to exhibit a redshit and a blueshift. These chemical shifts originate from the interaction between the C–H bond and highly electronegative oxygen. The bonding structures of SiOC films can be divided into two types depending on the observed chemical shifts and consist of a Si–O–C cross-link structure and a Si–O–C cage-link structure. The blue shift in SiOC films is associated with the porosity due to an increase in the number of electron-rich groups, such as methyl radicals, resulting in the formation of a Si–O–C cage link structure. On the other hand, the Si–O–C cross-link structure associated with a redshift is generated from the adhesion due to C–H bond elongation.

Novel mechanisms for core level shifts in organic compounds

In the analysis of the shifts of the core level binding energies of atoms in molecules, it is standard to consider only the effective charges of the ionized atom and of its surroundings. In the present work, we give very strong evidence that another mechanism makes important contributions to core level binding energy shifts. This mechanism is the involvement of the deeper lying valence levels in the chemical bonding. In the present paper, we specifically consider the involvement of the N(2s) electrons in the bonding for pyridine and pyrrole. We show that the the difference of this involvement in these two molecules is comparable in magnitude to the observed, ≈1 eV, difference of the N(1s) binding energies. We describe the 2s involvement as hybridization; evidence that this is an appropriate description is presented. For the first time, we have been able to directly determine the hybridization contribution to the chemical shift of the core level binding energies. It is likely that this mechanism needs to be considered, in general, for the proper analysis and interpretation of the core level chemical shifts measured with X-ray photoelectron spectroscopy because hybridization makes important contributions to the chemical bonding. © 1997 Elsevier Science B.V.

ChemInform Abstract: Prediction of Nitrogen and Oxygen NMR Chemical Shifts in Organic Compounds by Density Functional Theory

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Prediction of Nitrogen and Oxygen NMR Chemical Shifts in Organic Compounds by Density Functional Theory

Sum-over-states density functional perturbation theory (SOS-DFPT) and Hartree−Fock (HF) theory based on the “individual gauge for localized orbitals” (IGLO) scheme were used to calculate 13C, 14N/15N, and 17O NMR chemical shifts of 23 molecules. Employing the (11s7p2d/6s2p)[7s6p2d/4s2p] basis set, SOS-DFPT chemical shifts were obtained that are clearly better than HF- or UDFT-based chemical shifts, as is reflected by mean absolute deviations of 2.8 (SOS-DFPT), 7.6 (UDFT), and 5.6 ppm (HF) for 13C chemical shifts, 11.8, 22.1, and 100.5 ppm for 14N/15N chemical shifts, and 36.4, 57.2, and 45.7 ppm for 17O chemical shifts with regard to experimental values. By estimating appropriate gas phase values for 14N/15N chemical shifts from measured solvent effects, average errors of SOS-DFPT chemical shifts are reduced to 3 ppm, which is close to uncertainties in experimental values. SOS-DFPT is the method of choice for predicting reasonably accurate NMR chemical shifts at relatively low computational cost even in c...

15N chemical shifts in organic compounds

Concepts in Magnetic ResonanceVolume 7, Issue 3 p. 243-243 Article 15N chemical shifts in organic compounds First published: 1995 https://doi.org/10.1002/cmr.1820070305AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume7, Issue31995Pages 243-243 RelatedInformation

15N chemical shifts in organic compounds

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Tritium nuclear magnetic resonance spectroscopy. Part 11. Further consideration of referencing, isotope effects and coupling constants: Preparation of [3H]tetramethylsilane

AbstractSmall discrepancies between 3H and 1H chemical shifts in organic compounds led to the finding that the ratio of Larmor frequencies ωT/ωH depends on the carbon‐hydrogen bond hybridisation. The ‘best’ ratio for ghost referencing of 3H NMR spectra was then determined from measurements on purified partially tritiated TMS as 1.066639738±2 × 10−9. Some 3H isotope effects on chemical shifts are listed and the 3H isotope effect on the methylene geminal coupling constant in benzyl methyl sulphoxide is measured. Use of 2H in the measurement of 2J(HH) coupling constants has inherent disadvantages, overcome by use of 3H substitution.

14N chemical shifts in organic compounds

Quadrupole broadening of nitrogen nuclear resonances can be minimized by using solvents of low viscosity. An extensive survey is presented of 14N chemical shifts in organic compounds.