NMRsolvents - NMR Chemical Shifts of Common Laboratory...

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Unformatted text preview: NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities Hugo E. Gottlieb,* Vadim Kotlyar, and Abraham Nudelman* Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel Received June 27, 1997 In the course of the routine use of NMR as an aid for organic chemistry, a day-to-day problem is the identifica-tion of signals deriving from common contaminants (water, solvents, stabilizers, oils) in less-than-analyti-cally-pure samples. This data may be available in the literature, but the time involved in searching for it may be considerable. Another issue is the concentration dependence of chemical shifts (especially 1 H); results obtained two or three decades ago usually refer to much more concentrated samples, and run at lower magnetic fields, than todays practice. We therefore decided to collect 1 H and 13 C chemical shifts of what are, in our experience, the most popular extra peaks in a variety of commonly used NMR solvents, in the hope that this will be of assistance to the practicing chemist. Experimental Section NMR spectra were taken in a Bruker DPX-300 instrument (300.1 and 75.5 MHz for 1 H and 13 C, respectively). Unless otherwise indicated, all were run at room temperature (24 ( 1 C). For the experiments in the last section of this paper, probe temperatures were measured with a calibrated Eurotherm 840/T digital thermometer, connected to a thermocouple which was introduced into an NMR tube filled with mineral oil to ap-proximately the same level as a typical sample. At each temperature, the D 2 O samples were left to equilibrate for at least 10 min before the data were collected. In order to avoid having to obtain hundreds of spectra, we prepared seven stock solutions containing approximately equal amounts of several of our entries, chosen in such a way as to prevent intermolecular interactions and possible ambiguities in assignment. Solution 1: acetone, tert-butyl methyl ether, di-methylformamide, ethanol, toluene. Solution 2: benzene, di-methyl sulfoxide, ethyl acetate, methanol. Solution 3: acetic acid, chloroform, diethyl ether, 2-propanol, tetrahydrofuran. Solution 4: acetonitrile, dichloromethane, dioxane, n-hexane, HMPA. Solution 5: 1,2-dichloroethane, ethyl methyl ketone, n-pentane, pyridine. Solution 6: tert-butyl alcohol, BHT, cyclo-hexane, 1,2-dimethoxyethane, nitromethane, silicone grease, triethylamine. Solution 7: diglyme, dimethylacetamide, ethyl-ene glycol, grease (engine oil). For D 2 O. Solution 1: acetone, tert-butyl methyl ether, dimethylformamide, ethanol, 2-propanol. Solution 2: dimethyl sulfoxide, ethyl acetate, ethylene glycol, methanol. Solution 3: acetonitrile, diglyme, dioxane, HMPA, pyridine. Solution 4: 1,2-dimethoxyethane, dimethylacetamide, ethyl methyl ketone, triethylamine. Solution 5: acetic acid, tert-butyl alcohol, diethyl ether, tetrahydrofuran. In D 2 O and CD 3 OD nitromethane was run separately, as the protons exchanged with deuterium in presence of triethylamine. exchanged with deuterium in presence of triethylamine....
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NMRsolvents - NMR Chemical Shifts of Common Laboratory...

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