1、NMR Chemical Shifts of CommonLaboratory Solvents as Trace ImpuritiesHugo E. Gottlieb,* Vadim Kotlyar, andAbraham Nudelman*Department of Chemistry, Bar-Ilan University,Ramat-Gan 52900, IsraelReceived June 27, 1997In the course of the routine use of NMR as an aid fororganicchemistry,aday-to-dayproblem
2、istheidentifica-tion of signals deriving from common contaminants(water, solvents, stabilizers, oils) in less-than-analyti-cally-pure samples. This data may be available in theliterature,butthetimeinvolvedinsearchingforitmaybe considerable. Another issue is the concentrationdependence of chemical sh
3、ifts (especially1H); resultsobtainedtwoorthreedecadesagousuallyrefertomuchmore concentrated samples, and run at lower magneticfields, than todays practice.We therefore decided to collect1H and13C chemicalshifts of what are, in our experience, the most popular“extra peaks” in a variety of commonly us
4、ed NMRsolvents, in the hope that this will be of assistance tothe practicing chemist.Experimental SectionNMR spectra were taken in a Bruker DPX-300 instrument(300.1 and 75.5 MHz for1H and13C, respectively). Unlessotherwise indicated, all were run at room temperature (24 ( 1C). Fortheexperimentsinthe
5、lastsectionofthispaper,probetemperaturesweremeasuredwithacalibratedEurotherm840/Tdigital thermometer, connected to a thermocouple which wasintroduced into an NMR tube filled with mineral oil to ap-proximately the same level as a typical sample. At eachtemperature,theD2Osampleswerelefttoequilibratefo
6、ratleast10 min before the data were collected.In order to avoid having to obtain hundreds of spectra, wepreparedsevenstocksolutionscontainingapproximatelyequalamounts of several of our entries, chosen in such a way as topreventintermolecularinteractionsandpossibleambiguitiesinassignment. Solution 1:
7、 acetone, tert-butyl methyl ether, di-methylformamide, ethanol, toluene. Solution 2: benzene, di-methyl sulfoxide, ethyl acetate, methanol. Solution 3: aceticacid, chloroform, diethyl ether, 2-propanol, tetrahydrofuran.Solution 4: acetonitrile, dichloromethane, dioxane, n-hexane,HMPA. Solution 5: 1,
8、2-dichloroethane, ethyl methyl ketone,n-pentane,pyridine. Solution6: tert-butylalcohol,BHT,cyclo-hexane, 1,2-dimethoxyethane, nitromethane, silicone grease,triethylamine. Solution7: diglyme,dimethylacetamide,ethyl-eneglycol,“grease”(engineoil). ForD2O. Solution1: acetone,tert-butylmethylether,dimeth
9、ylformamide,ethanol,2-propanol.Solution 2: dimethyl sulfoxide, ethyl acetate, ethylene glycol,methanol. Solution 3: acetonitrile, diglyme, dioxane, HMPA,pyridine. Solution4: 1,2-dimethoxyethane,dimethylacetamide,ethylmethylketone,triethylamine. Solution5: aceticacid,tert-butyl alcohol, diethyl ether
10、, tetrahydrofuran. In D2O andCD3OD nitromethane was run separately, as the protonsexchanged with deuterium in presence of triethylamine.ResultsProtonSpectra(Table1). Asampleof0.6mLofthesolvent, containing 1 L of TMS,1was first run on itsown. From this spectrum we determined the chemicalshifts of the
11、 solvent residual peak2and 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. Incontrast, in e.g. DMSO the water is
12、already stronglyhydrogen-bondedtothesolvent,andsoluteshaveonlyanegligible effect on its chemical shift. This is also truefor D2O; the chemical shift of the residual HDO is verytemperature-dependent(videinfra)but,maybecounter-intuitively, remarkably solute (and pH) independent.We then added 3 L of on
13、e of our stock solutions tothe NMR tube. The chemical shifts were read and arepresented in Table 1. Except where indicated, thecoupling constants, and therefore the peak shapes, areessentially solvent-independent and are presented onlyonce.For D2O as a solvent, the accepted reference peak ( ) 0)isth
14、emethylsignalofthesodiumsaltof3-(trimeth-ylsilyl)propanesulfonicacid;onecrystalofthiswasaddedtoeachNMRtube. Thismaterialhasseveraldisadvan-tages,however: itisnotvolatile,soitcannotbereadilyeliminatedifthesamplehastoberecovered. Inaddition,unless one purchases it in the relatively expensivedeuterated
15、 form, it adds three more signals to thespectrum (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; wefind that if the effects of temperature are taken intoaccount(videinfra),thisisveryreproducible. ForD2
16、O,we used a different set of stock solutions, since many ofthe less polar substrates are not significantly water-soluble (see Table 1). We also ran sodium acetate andsodium formate (chemical shifts: 1.90 and 8.44 ppm,respectively).Carbon Spectra (Table 2). To each tube, 50 Lofthe stock solution and
17、3 LofTMS1were added. Thesolvent chemical shifts3were obtained from the spectracontainingthesolutes,andtherangesofchemicalshifts(1)For recommendations on the publication of NMR data, see:IUPAC Commission on Molecular Structure and Spectroscopy. PureAppl. Chem. 1972, 29, 627; 1976, 45, 217.(2)I.e., th
18、e signal of the proton for the isotopomer with one lessdeuterium than the perdeuterated material, e.g.,CHCl3in CDCl3orC6D5HinC6D6. ExceptforCHCl3,thesplittingduetoJHDistypicallyobserved (to a good approximation, it is 1/6.5 of the value of thecorresponding JHH). For CHD2groups (deuterated acetone, D
19、MSO,acetonitrile), this signal is a 1:2:3:2:1 quintet with a splitting of ca.2Hz.(3)In contrast to what was said in note 2, in the13C spectra thesolvent 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
20、 of HDO as a function of tempera-ture.7512 J. Org. Chem. 1997, 62, 7512-7515S0022-3263(97)01176-6 CCC: $14.00 1997 American Chemical Societyshow their degree of variability. Occasionally, in orderto distinguish between peaks whose assignment wasambiguous,afurther1-2 Lofaspecificsubstratewereadded an
21、d the spectra run again.Table 1.1H NMR Dataproton mult CDCl3(CD3)2CO (CD3)2SO C6D6CD3CN CD3OD D2Osolventresidualpeak 7.26 2.05 2.50 7.16 1.94 3.31 4.79H2O s 1.56 2.84a3.33a0.40 2.13 4.87aceticacid CH3s 2.10 1.96 1.91 1.55 1.96 1.99 2.08acetone CH3s 2.17 2.09 2.09 1.55 2.08 2.15 2.22acetonitrile CH3s
22、 2.10 2.05 2.07 1.55 1.96 2.03 2.06benzene CH s 7.36 7.36 7.37 7.15 7.37 7.33tert-butylalcohol CH3s 1.28 1.18 1.11 1.05 1.16 1.40 1.24OHcs 4.19 1.55 2.18tert-butylmethylether CCH3s 1.19 1.13 1.11 1.07 1.14 1.15 1.21OCH3s 3.22 3.13 3.08 3.04 3.13 3.20 3.22BHTbArH s 6.98 6.96 6.87 7.05 6.97 6.92OHcs 5
23、.01 6.65 4.79 5.20ArCH3s 2.27 2.22 2.18 2.24 2.22 2.21ArC(CH3)3s 1.43 1.41 1.36 1.38 1.39 1.40chloroform CH s 7.26 8.02 8.32 6.15 7.58 7.90cyclohexane CH2s 1.43 1.43 1.40 1.40 1.44 1.451,2-dichloroethane CH2s 3.73 3.87 3.90 2.90 3.81 3.78dichloromethane CH2s 5.30 5.63 5.76 4.27 5.44 5.49diethylether
24、 CH3t,7 1.21 1.11 1.09 1.11 1.12 1.18 1.17CH2q,7 3.48 3.41 3.38 3.26 3.42 3.49 3.56diglyme CH2m 3.65 3.56 3.51 3.46 3.53 3.61 3.67CH2m 3.57 3.47 3.38 3.34 3.45 3.58 3.61OCH3s 3.39 3.28 3.24 3.11 3.29 3.35 3.371,2-dimethoxyethane CH3s 3.40 3.28 3.24 3.12 3.28 3.35 3.37CH2s 3.55 3.46 3.43 3.33 3.45 3.
25、52 3.60dimethylacetamide CH3CO s 2.09 1.97 1.96 1.60 1.97 2.07 2.08NCH3s 3.02 3.00 2.94 2.57 2.96 3.31 3.06NCH3s 2.94 2.83 2.78 2.05 2.83 2.92 2.90dimethylformamide CH s 8.02 7.96 7.95 7.63 7.92 7.97 7.92CH3s 2.96 2.94 2.89 2.36 2.89 2.99 3.01CH3s 2.88 2.78 2.73 1.86 2.77 2.86 2.85dimethylsulfoxide
26、CH3s 2.62 2.52 2.54 1.68 2.50 2.65 2.71dioxane CH2s 3.71 3.59 3.57 3.35 3.60 3.66 3.75ethanol CH3t,7 1.25 1.12 1.06 0.96 1.12 1.19 1.17CH2q,7d3.72 3.57 3.44 3.34 3.54 3.60 3.65OH sc,d1.32 3.39 4.63 2.47ethylacetate CH3CO s 2.05 1.97 1.99 1.65 1.97 2.01 2.07CH2CH3q,7 4.12 4.05 4.03 3.89 4.06 4.09 4.1
27、4CH2CH3t,7 1.26 1.20 1.17 0.92 1.20 1.24 1.24ethylmethylketone CH3CO s 2.14 2.07 2.07 1.58 2.06 2.12 2.19CH2CH3q,7 2.46 2.45 2.43 1.81 2.43 2.50 3.18CH2CH3t,7 1.06 0.96 0.91 0.85 0.96 1.01 1.26ethyleneglycol CH se3.76 3.28 3.34 3.41 3.51 3.59 3.65“grease”fCH3m 0.86 0.87 0.92 0.86 0.88CH2brs 1.26 1.2
28、9 1.36 1.27 1.29n-hexane CH3t 0.88 0.88 0.86 0.89 0.89 0.90CH2m 1.26 1.28 1.25 1.24 1.28 1.29HMPAgCH3d,9.5 2.65 2.59 2.53 2.40 2.57 2.64 2.61methanol CH3sh3.49 3.31 3.16 3.07 3.28 3.34 3.34OH sc,h1.09 3.12 4.01 2.16nitromethane CH3s 4.33 4.43 4.42 2.94 4.31 4.34 4.40n-pentane CH3t,7 0.88 0.88 0.86 0
29、.87 0.89 0.90CH2m 1.27 1.27 1.27 1.23 1.29 1.292-propanol CH3d,6 1.22 1.10 1.04 0.95 1.09 1.50 1.17CH sep,6 4.04 3.90 3.78 3.67 3.87 3.92 4.02pyridine CH(2) m 8.62 8.58 8.58 8.53 8.57 8.53 8.52CH(3) m 7.29 7.35 7.39 6.66 7.33 7.44 7.45CH(4) m 7.68 7.76 7.79 6.98 7.73 7.85 7.87siliconegreaseiCH3s 0.0
30、7 0.13 0.29 0.08 0.10tetrahydrofuran CH2m 1.85 1.79 1.76 1.40 1.80 1.87 1.88CH2O m 3.76 3.63 3.60 3.57 3.64 3.71 3.74toluene CH3s 2.36 2.32 2.30 2.11 2.33 2.32CH(o/p) m 7.17 7.1-7.2 7.18 7.02 7.1-7.3 7.16CH(m) m 7.25 7.1-7.2 7.25 7.13 7.1-7.3 7.16triethylamine CH3t,7 1.03 0.96 0.93 0.96 0.96 1.05 0.
31、99CH2q,7 2.53 2.45 2.43 2.40 2.45 2.58 2.57aInthesesolventstheintermolecularrateofexchangeisslowenoughthatapeakduetoHDOisusuallyalsoobserved;itappearsat2.81 and 3.30 ppm in acetone and DMSO, respectively. In the former solvent, it is often seen as a 1:1:1 triplet, with2JH,D) 1 Hz.b2,6-Dimethyl-4-ter
32、t-butylphenol.cThe signals from exchangeable protons were not always identified.dIn some cases (see note a), thecouplinginteractionbetweentheCH2andtheOHprotonsmaybeobserved(J ) 5Hz).eInCD3CN,theOHprotonwasseenasamultipletat 2.69, and extra coupling was also apparent on the methylene peak.fLong-chain
33、, linear aliphatic hydrocarbons. Their solubility inDMSOwastoolowtogivevisiblepeaks.gHexamethylphosphoramide.hInsomecases(seenotesa,d),thecouplinginteractionbetweenthe CH3and the OH protons may be observed (J ) 5.5 Hz).iPoly(dimethylsiloxane). Its solubility in DMSO was too low to give visiblepeaks.
34、Notes J. Org. Chem., Vol. 62, No. 21, 1997 7513Table 2.13C NMR DataaCDCl3(CD3)2CO (CD3)2SO C6D6CD3CN CD3OD D2Osolventsignals 77.16 ( 0.06 29.84 ( 0.01 39.52 ( 0.06 128.06 ( 0.02 1.32 ( 0.02 49.00(0.01206.26 ( 0.13 118.26 ( 0.02aceticacid CO 175.99 172.31 171.93 175.82 173.21 175.11 177.21CH320.81 20
35、.51 20.95 20.37 20.73 20.56 21.03acetone CO 207.07 205.87 206.31 204.43 207.43 209.67 215.94CH330.92 30.60 30.56 30.14 30.91 30.67 30.89acetonitrile CN 116.43 117.60 117.91 116.02 118.26 118.06 119.68CH31.89 1.12 1.03 0.20 1.79 0.85 1.47benzene CH 128.37 129.15 128.30 128.62 129.32 129.34tert-butyla
36、lcohol C 69.15 68.13 66.88 68.19 68.74 69.40 70.36CH331.25 30.72 30.38 30.47 30.68 30.91 30.29tert-butylmethylether OCH349.45 49.35 48.70 49.19 49.52 49.66 49.37C 72.87 72.81 72.04 72.40 73.17 74.32 75.62CCH326.99 27.24 26.79 27.09 27.28 27.22 26.60BHT C(1) 151.55 152.51 151.47 152.05 152.42 152.85C
37、(2) 135.87 138.19 139.12 136.08 138.13 139.09CH(3) 125.55 129.05 127.97 128.52 129.61 129.49C(4) 128.27 126.03 124.85 125.83 126.38 126.11CH3Ar 21.20 21.31 20.97 21.40 21.23 21.38CH3C 30.33 31.61 31.25 31.34 31.50 31.15C 34.25 35.00 34.33 34.35 35.05 35.36chloroform CH 77.36 79.19 79.16 77.79 79.17
38、79.44cyclohexane CH226.94 27.51 26.33 27.23 27.63 27.961,2-dichloroethane CH243.50 45.25 45.02 43.59 45.54 45.11dichloromethane CH253.52 54.95 54.84 53.46 55.32 54.78diethylether CH315.20 15.78 15.12 15.46 15.63 15.46 14.77CH265.91 66.12 62.05 65.94 66.32 66.88 66.42diglyme CH359.01 58.77 57.98 58.6
39、6 58.90 59.06 58.67CH270.51 71.03 69.54 70.87 70.99 71.33 70.05CH271.90 72.63 71.25 72.35 72.63 72.92 71.631,2-dimethoxyethane CH359.08 58.45 58.01 58.68 58.89 59.06 58.67CH271.84 72.47 17.07 72.21 72.47 72.72 71.49dimethylacetamide CH321.53 21.51 21.29 21.16 21.76 21.32 21.09CO 171.07 170.61 169.54
40、 169.95 171.31 173.32 174.57NCH335.28 34.89 37.38 34.67 35.17 35.50 35.03NCH338.13 37.92 34.42 37.03 38.26 38.43 38.76dimethylformamide CH 162.62 162.79 162.29 162.13 163.31 164.73 165.53CH336.50 36.15 35.73 35.25 36.57 36.89 37.54CH331.45 31.03 30.73 30.72 31.32 31.61 32.03dimethylsulfoxide CH340.7
41、6 41.23 40.45 40.03 41.31 40.45 39.39dioxane CH267.14 67.60 66.36 67.16 67.72 68.11 67.19ethanol CH318.41 18.89 18.51 18.72 18.80 18.40 17.47CH258.28 57.72 56.07 57.86 57.96 58.26 58.05ethylacetate CH3CO 21.04 20.83 20.68 20.56 21.16 20.88 21.15CO 171.36 170.96 170.31 170.44 171.68 172.89 175.26CH26
42、0.49 60.56 59.74 60.21 60.98 61.50 62.32CH314.19 14.50 14.40 14.19 14.54 14.49 13.92ethylmethylketone CH3CO 29.49 29.30 29.26 28.56 29.60 29.39 29.49CO 209.56 208.30 208.72 206.55 209.88 212.16 218.43CH2CH336.89 36.75 35.83 36.36 37.09 37.34 37.27CH2CH37.86 8.03 7.61 7.91 8.14 8.09 7.87ethyleneglyco
43、l CH263.79 64.26 62.76 64.34 64.22 64.30 63.17“grease” CH229.76 30.73 29.20 30.21 30.86 31.29n-hexane CH314.14 14.34 13.88 14.32 14.43 14.45CH2(2) 22.70 23.28 22.05 23.04 23.40 23.68CH2(3) 31.64 32.30 30.95 31.96 32.36 32.73HMPAbCH336.87 37.04 36.42 36.88 37.10 37.00 36.46methanol CH350.41 49.77 48.
44、59 49.97 49.90 49.86 49.50cnitromethane CH362.50 63.21 63.28 61.16 63.66 63.08 63.22n-pentane CH314.08 14.29 13.28 14.25 14.37 14.39CH2(2) 22.38 22.98 21.70 22.72 23.08 23.38CH2(3) 34.16 34.83 33.48 34.45 34.89 35.302-propanol CH325.14 25.67 25.43 25.18 25.55 25.27 24.38CH 64.50 63.85 64.92 64.23 64
45、.30 64.71 64.88pyridine CH(2) 149.90 150.67 149.58 150.27 150.76 150.07 149.18CH(3) 123.75 124.57 123.84 123.58 127.76 125.53 125.12CH(4) 135.96 136.56 136.05 135.28 136.89 138.35 138.27siliconegrease CH31.04 1.40 1.38 2.10tetrahydrofuran CH225.62 26.15 25.14 25.72 26.27 26.48 25.67CH2O 67.97 68.07
46、67.03 67.80 68.33 68.83 68.68toluene CH321.46 21.46 20.99 21.10 21.50 21.50C(i) 137.89 138.48 137.35 137.91 138.90 138.85CH(o) 129.07 129.76 128.88 129.33 129.94 129.91CH(m) 128.26 129.03 128.18 128.56 129.23 129.20CH(p) 125.33 126.12 125.29 125.68 126.28 126.29triethylamine CH311.61 12.49 11.74 12.
47、35 12.38 11.09 9.07CH246.25 47.07 45.74 46.77 47.10 46.96 47.19aSee footnotes for Table 1.b 2JPC) 3 Hz.cReference material; see text.7514 J. Org. Chem., Vol. 62, No. 21, 1997 NotesFor D2O solutions there is no accepted reference forcarbonchemicalshifts. Wesuggesttheadditionofadropof methanol, and th
48、e position of its signal to be definedas 49.50 ppm; on this basis, the entries in Table 2 wererecorded. Thechemicalshiftsthusobtainedare,onthewhole, very similar to those for the other solvents.Alternatively, we suggest the use of dioxane when themethanol peak is expected to fall in a crowded area o
49、fthe spectrum. We also report the chemical shifts ofsodiumformate(171.67ppm),sodiumacetate(182.02and23.97 ppm), sodium carbonate (168.88 ppm), sodiumbicarbonate(161.08ppm),andsodium3-(trimethylsilyl)-propanesulfonate 54.90, 19.66, 15.56 (methylenes 1, 2,and 3, respectively), and -2.04 ppm (methyls), in D2O.Temperature Dependence of HDO ChemicalShifts. Werecordedthe1HspectrumofasampleofD2O,containingacrystalofsodium3-(trimethylsilyl)propane-sulfonateasreference,asafunctionoftemperature.Thedata are shown in Figure 1. The solid line connectingthe experimental points corresponds to the equat
