Solvents spectrum referencing

Proton-decoupled P spectrum, referenced to 85% aqueous H3PO4 at 291K. The linear increase of the P NMR shift for PH3 in various solvents (CCI4, benzene, toluene, and cyclohexane) with increasing temperature (30 to 90°C) is illustrated in the paper [8]. J(P-H) was taken from [12]. 

Figure Bl.11.9. Integrated 250 MHz H NMR spectrum of dilute propan-1-ol in dinrethylsulfoxide solvent. Here, the shift order parallels the chemical order. Arr expansion of the H2-I nrultiplet is included, as is the implicit frequency scale, also referenced here to TMS = 0.

Dicarbaundecaborane(13) is a white hygroscopic solid which is soluble in water, alcohols, and aromatic solvents. It is best stored cold in a dry, inert atmosphere. The proton-decoupled nB NMR spectrum (115 MHz, C6D6, referenced to external BF3OEt2) shows peaks at d 4.0 (2 B), - 4.4 (2 B), - 16.4 (1 B), - 17.0 (1 B), and - 27.4 (3 B). The complex is a diprotic acid with pK i of 2.98 and pKa2 of 14.25.6 Deprotonation of C2B9H13 with butyl lithium in benzene affords anhydrous Li2C2B9Hi... 

Other reference substances are available and can be used as well. Sometimes the resonance of the actual solvent can serve as a reference. Preferably, the referencing method used for the sample should be the same as that used for the authentic reference sample (or library spectrum), or at least the scale... 

An attractive alternative to the use of TMS as a primary reference is its use as a secondary reference. In this method, a spectrum is referenced to the signal of the residual proton(s) in a deuterated solvent (e.g., the small amount of CHCI3 at b 7.26 in CDCI3), while a spectrum is referenced to the carbon(s) of the solvent (e.g., the middle line of the three-line resonance of CDCI3 at 8 77.00). The chemical shifts of the carbons and residual protons of the more common solvents are presented in Table 2-1. The two water soluble,... 

Figure 4. Proton magnetic resonance spectroscopy of the anomeric proton region of peptidophosphomannan (10). Fifty mg of peptidophosphomannan was dissolved in H20 and held at room temperature for 1 hr. The solvent was removed under reduced pressure and the residue redissolved in 1 mL H20. The NMR spectrum was taken on a Varian XL-100 MHz spectrometer at 29°C with the instrument locked on deuterium and referenced to an internal standard of sodium 2,2-dimethyl-2-silapentane-5-sulfonate.

When preparing a sample it is common practice to add a suitable compound to act as an internal chemical shift reference in the spectrum, and the selection of this must be suitable for the analyte and the solvent. In proton and carbon NMR, the reference used in organic solvents is tetramethylsilane (TMS, 0.0 ppm), which has a number of favourable properties it has a sharp 12-proton singlet resonance that falls conveniently to one end of the spectrum, and it is volatile so can be readily removed and it is chemically inert. In a few cases, this material may be unsuitable, such as in the study of silanes or cyclopropanes. For routine work, it is often not necessary to add any internal reference as the residual lines of the solvent itself can serve this purpose (Table 3.2). For aqueous solutions, the water soluble equivalent of TMS is partially deuterated sodium 3-(trimethylsilyl)propionate-d4 (TSP-dt), which is also referenced to 0.0ppm. A volatile alternative is 1,4-dioxane ( H 3.75 ppm,... 

A HEWLETT-PACKARD 5950B ESCA spectrometer was utilized in the ESCA studies of solvent cast block copolyether-urethane-urea, copolyurethane-urea, polyurea and isotactic polypropylene oxide films. The samples were allowed to come to equilibrium at 10" Torr at 300°K prior to data collection. The X-rays from the Al(K j 2) line at 1487 eV were used. Samples were scanned 10 times witft a scan width of 20 eV centered around elemental spectra of interest C(ls) 290-270 eV N(ls) 405-385 eV 0(ls) 540-520 eV. Radiation damage was evaluated by overlaying the carbon spectrum obtained first for each sample and one obtained after all other elements of interest were scanned. Differences in spectra were within experimental error, therefore radiation damage was considered to be negligible for the qualitative studies. All bands were referenced to the 285 eV band of the C(ls) spectrum for each sample. Peak areas were determined digitally and by planimeter. 

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