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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 today’s 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.
Results
Proton Spectra (Table 1). A sample of 0.6 mL of the
solvent, containing 1 µL of TMS,
1
was first run on its
own. From this spectrum we determined the chemical
shifts of the solvent residual peak
2
and the water peak.
It should be noted that the latter is quite temperature-
dependent (vide infra). Also, any potential hydrogen-
bond acceptor will tend to shift the water signal down-
field; this is particularly true for nonpolar solvents. In
contrast, in e.g. DMSO the water is already strongly
hydrogen-bonded to the solvent, and solutes have only a
negligible effect on its chemical shift. This is also true
for D
2
O; the chemical shift of the residual HDO is very
temperature-dependent (vide infra) but, maybe counter-
intuitively, remarkably solute (and pH) independent.
We then added 3 µL of one of our stock solutions to
the NMR tube. The chemical shifts were read and are
presented in Table 1. Except where indicated, the
coupling constants, and therefore the peak shapes, are
essentially solvent-independent and are presented only
once.
For D
2
O as a solvent, the accepted reference peak (δ
) 0) is the methyl signal of the sodium salt of 3-(trimeth-
ylsilyl)propanesulfonic acid; one crystal of this was added
to each NMR tube. This material has several disadvan-
tages, however: it is not volatile, so it cannot be readily
eliminated if the sample has to be recovered. In addition,
unless one purchases it in the relatively expensive
deuterated form, it adds three more signals to the
spectrum (methylenes 1, 2, and 3 appear at 2.91, 1.76,
and 0.63 ppm, respectively). We suggest that the re-
sidual HDO peak be used as a secondary reference; we
find that if the effects of temperature are taken into
account (vide infra), this is very reproducible. For D
2
O,
we used a different set of stock solutions, since many of
the less polar substrates are not significantly water-
soluble (see Table 1). We also ran sodium acetate and
sodium formate (chemical shifts: 1.90 and 8.44 ppm,
respectively).
Carbon Spectra (Table 2). To each tube, 50 µLof
the stock solution and 3 µLofTMS
1
were added. The
solvent chemical shifts
3
were obtained from the spectra
containing the solutes, and the ranges of chemical shifts
(1) For recommendations on the publication of NMR data, see:
IUPAC Commission on Molecular Structure and Spectroscopy. Pure
Appl. Chem. 1972, 29, 627; 1976, 45, 217.
(2) I.e., the signal of the proton for the isotopomer with one less
deuterium than the perdeuterated material, e.g.,CHCl
3
in CDCl
3
or
C
6
D
5
H in C
6
D
6
. Except for CHCl
3
, the splitting due to J
HD
is typically
observed (to a good approximation, it is 1/6.5 of the value of the
corresponding J
HH
). For CHD
2
groups (deuterated acetone, DMSO,
acetonitrile), this signal is a 1:2:3:2:1 quintet with a splitting of ca.2
Hz.
(3) In contrast to what was said in note 2, in the
13
C spectra the
solvent signal is due to the perdeuterated isotopomer, and the one-
bond couplings to deuterium are always observable (ca.20-30 Hz).
Figure 1. Chemical shift of HDO as a function of tempera-
ture.
7512 J. Org. Chem. 1997, 62, 7512-7515
S0022-3263(97)01176-6 CCC: $14.00 © 1997 American Chemical Society
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