Tetramethylsilane

Deuteroacetone, internal tetramethylsilane. Values in deuterochloroform can be found in Ref. 64,... 

The molar diamagnetic susceptibility of thiazole and some derivatives was initially determined by the classical Curie-Cheneveau method (5,315,316) and later confirmed by a method (317) based on the difference of NMR proton chemical shift of a sample of tetramethylsilane immersed in the liquid to be investigated, according to the shape (cylindrical or spherical) of the sample tube (Table 1-47) (318),... 

Instead of measuring chemical shifts m absolute terms we measure them with respect to a standard—tetramethylsilane ( 113)481 abbreviated TMS The protons of TMS are more shielded than those of most organic compounds so all of the signals m... 

Approximate values relative to tetramethylsilane other groups within the molecule can cause a proton signal to appear outside of the range cited... 

Just as chemical shifts in H NMR are measured relative to the protons of tetramethylsi lane chemical shifts m NMR are measured relative to the carbons of tetramethylsilane Table 13 3 lists typical chemical shift ranges for some representative types of carbon atoms In general the factors that most affect chemical shifts are... 

Tetramethylsilane (TIMS) (Section 13 4) The molecule (CH3)4Si used as a standard to calibrate proton and carbon 13 NMR spectra... 

TABLE 7.47 Proton Chemical Shifts of Reference Compounds Relative to tetramethylsilane. 

TABLE 7.50 Estimation of Chemical Shifts of Alkane Carbons Relative to tetramethylsilane. 

TABLE 7.60 Carbon-13 Chemical Shifts of Deuterated Solvents Relative to tetramethylsilane. 

By trapping PX at liquid nitrogen temperature and transferring it to THF at —80° C, the nmr spectmm could be observed (9). It consists of two sharp peaks of equal area at chemical shifts of 5.10 and 6.49 ppm downfield from tetramethylsilane (TMS). The fact that any sharp peaks are observed at all attests to the absence of any significant concentration of unpaired electron spins, such as those that would be contributed by the biradical (11). Furthermore, the chemical shift of the ring protons, 6.49 ppm, is well upheld from the typical aromatic range and more characteristic of an oletinic proton. Thus the olefin stmcture (1) for PX is also supported by nmr. 

Proton nmr. In the simplest experiment, the sample and a small amount of a reference compound such as tetramethylsilane [75-76-3] (TMS), are placed in a tube, usually of 5-mm diameter. Typical samples may be a neat Hquid or a solution containing as Htde solute as 0.01 mg/cm. The... 

J3 4 = 3.45-4.35 J2-4 = 1.25-1.7 and J2-5 = 3.2-3.65 Hz. The technique can be used quantitatively by comparison with standard spectra of materials of known purity. C-nmr spectroscopy of thiophene and thiophene derivatives is also a valuable technique that shows well-defined patterns of spectra. C chemical shifts for thiophene, from tetramethylsilane (TMS), are 127.6, C 125.9, C 125.9, and C 127.6 ppm. 

Gem dmelhylation ot cyclohexane denvatives (vicinal dihalocyciohexanes or methylcyclohexane) with tetramethylsilane (TMS) and AIX3... 

Tetramethylsilane (TMS) [75-76-3] M 88.2, b 26.3, n 1.359, d 0.639. Distilled from cone H2SO4 (after shaking with it) or LiAlH4, through a 5ft vacuum-jacketted column packed with glass helices into an ice-cooled condenser, then percolated through silica gel to remove traces of halide. 

It is convenient to reference the chemical shift to a standard such as tetramethylsilane [TMS, (C//j)4Si] rather than to the proton fC. Thus, a frequency difference (Hz) is measured for a proton or a carbon-13 nucleus of a sample from the H or C resonance of TMS. This value is divided by the absolute value of the Larmor frequency of the standard (e.g. 400 MHz for the protons and 100 MHz for the carbon-13 nuclei of TMS when using a 400 MHz spectrometer), which itself is proportional to the strength Bg of the magnetic field. The chemical shift is therefore given in parts per million (ppm, 5 scale, Sh for protons, 5c for carbon-13 nuclei), because a frequency difference in Hz is divided by a frequency in MHz, these values being in a proportion of 1 1O. ... 

FIGURE 13.7 The200-MHz H NMR spectrum of chloroform (HCCb). Chemical shifts are measured along the x-axis in parts per million (ppm) from tetramethylsilane as the reference, which is assigned a value of zero. 

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