Natural abundance determination of 13C chemical shifts in the gas phase. Direct gas phase measurements and extrapolation from liquid phase measurements

AbstractHigh-resolution gas phase measurements of 1H NMR spectra at 400 MHz and atmospheric pressure of seven small hydrocarbons are presented. The developed new method and the experimental set-up are described. Ab initio GIAO MO calculations of 1H and 13C NMR absolute shieldings on the HF, MP2 and B3LYP levels using 25 standard gaussian basis sets are reported for these hydrocarbons, based on experimental re distances. The measured gas phase 1H chemical shifts have been converted to an absolute σ0 shielding scale by use of the literature shielding of methane. These and gas phase 13C literature values have been transferred with literature ZPV data to estimated σeexp shieldings which are used to evaluate the basis set dependence of the calculated σe shieldings utilizing linear least squares regressions. Exponential extrapolations of Dunning basis set calculations allow the determination of basis set limits for 1H and 13C shieldings. 1H and 13C chemical shifts have been derived from the HF calculated shieldings with shieldings of TMS which has been geometry optimized and GIAO calculated in each basis. Standard deviations (esd) as low as 0.09 ppm for 1H and 0.76 ppm for 13C calculations have been obtained.The statistically best basis set for simultaneous calculation of 1H and 13C absolute shieldings or relative shifts is 6-311G* within the HF and B3LYP methods. Aiming for highest accuracy and precision, 1H and 13C have to be treated separately. In this case, best results are obtained using MP2/6-311G** or higher for 1H shieldings and MP2/cc-pVTZ for 13C shieldings.

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Determination of Various Parameters during Thermal and Biological Pretreatment of Waste Materials

Energies ◽

10.3390/en13092262 ◽

2020 ◽

Vol 13 (9) ◽

pp. 2262 ◽

Cited By ~ 3

Author(s):

Robert Hren ◽

Aleksandra Petrovič ◽

Lidija Čuček ◽

Marjana Simonič

Keyword(s):

Liquid Phase ◽

Gas Phase ◽

Rumen Fluid ◽

Typha Latifolia ◽

Waste Materials ◽

Advantages And Disadvantages ◽

Before And After ◽

Ruminal Temperature ◽

Lower Temperature

Pretreatment of waste materials could help in more efficient waste management. Various pretreatment methods exist, each one having its own advantages and disadvantages. Moreover, a certain pretreatment technique might be efficient and economical for one feedstock while not for another. Thus, it is important to analyze how parameters change during pretreatment. In this study, two different pretreatment techniques were applied: thermal at lower and higher temperatures (38.6 °C and 80 °C) and biological, using cattle rumen fluid at ruminal temperature (≈38.6 °C). Two different feedstock materials were chosen: sewage sludge and riverbank grass (Typha latifolia), and their combinations (in a ratio of 1:1) were also analyzed. Various parameters were analyzed in the liquid phase before and after pretreatment, and in the gas phase after pretreatment. In the liquid phase, some of the parameters that are relevant to water quality were measured, while in the gas phase composition of biogas was measured. The results showed that most of the parameters significantly changed during pretreatments and that lower temperature thermal and/or biological treatment of grass and sludge is suggested for further applications.

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Gas phase 13C chemical shifts and coupling constants in the deuteromethanes

The Journal of Chemical Physics ◽

10.1063/1.435756 ◽

1978 ◽

Vol 68 (2) ◽

pp. 783-784 ◽

Cited By ~ 40

Author(s):

Mohammed Alei ◽

William E. Wageman

Keyword(s):

Gas Phase ◽

Chemical Shifts ◽

Coupling Constants ◽

13C Chemical Shifts

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Determination of Amphetamine and Methylamphetamine by Gas-liquid Chromatography (Head Space)

Human Toxicology ◽

10.1177/096032718300200236 ◽

1983 ◽

Vol 2 (2) ◽

pp. 391-393 ◽

Cited By ~ 3

Author(s):

D. Martinez ◽

M.P. Gimenez

Keyword(s):

Liquid Chromatography ◽

Solvent Extraction ◽

Liquid Phase ◽

Gas Phase ◽

Urine Sample ◽

Urine Samples ◽

Gas Liquid Chromatography ◽

Flame Detection ◽

Therapeutic Doses

1 A method for determining amphetamine and methylamphetamine in urine by gas-liquid chromatography is described. 2 Chromatography is performed on a 10% Apiezon L, 10% KOH column with alkali-flame detection (NPD). This method avoids the losses of these volatile substances which are known to occur when solvent extraction is used. An alkalinized urine sample (1 ml) is introduced into a sealed vial which is heated in a water bath at 70°C for 20 min. A 1 ml portion of the gas phase in equilibrium with the liquid phase is chromatographed. 3 Amphetamine and methylamphetamine can be detected and measured in urine samples after single therapeutic doses of the drugs.

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A 15N and 13C N.M.R. study of electron distribution in Di- and Tri-azapentadienium salts

Australian Journal of Chemistry ◽

10.1071/ch9781005 ◽

1978 ◽

Vol 31 (5) ◽

pp. 1005 ◽

Cited By ~ 5

Author(s):

AJ Jones ◽

H McNab ◽

P Hanisch

Keyword(s):

Density Distribution ◽

Electron Density ◽

Electron Density Distribution ◽

Electron Distribution ◽

Chemical Shifts ◽

Phenyl Group ◽

Natural Abundance ◽

Fourier Methods ◽

13C Chemical Shifts ◽

Electron Withdrawal

The 15N and 13C chemical shifts of eight vinamidinium and azavinamidinium cations have been determined at the natural-abundance level by means of Fourier methods. Both 15N and 13C chemical shifts reflect the electron- density distribution in the pentadienium chain, especially in the aryl derivatives in which conjugative stabilization through electron withdrawal by the substituent phenyl group is exhibited.

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