Proton nuclear magnetic resonance chemical shift

Proton nuclear magnetic resonance spectra of 15-20% solutions of polymers in CC14 were obtained with Varian T-60 or HR-300 spectrometers. Chemical shifts are reported... 

Proton nuclear magnetic resonance (NMR) chemical shifts of 1,2,3-thiadiazoles give another indication of the aromatic character of these compounds. Compiled in Table 4 are a number of examples of proton chemical shifts for ring-substituted 1,2,3-thiadiazoles. 

The proton nuclear magnetic resonance ( H NMR) spectrum of chitin was obtained in concentrated and deuterated hydrochloric acid (DCl) (Fig. 2.19). Chitin can be rapidly dissolved in concentrated acid after wetting in dilute acid. The assignment of the resonances and their chemical shifts (ppm) is given in Table 2.11. The NMR spectrum shows the... 

The proton nuclear magnetic resonance spectrum of lomefloxacin mesylate obtained in D2O at 25° C is given in Figure 5 (9). The spectrum was obtained on a Bruker AM-500 NMR Spectrometer operating at 500.13 MHz and was referenced to external TSP [3-(trimethylsilyl)propionic-2,2,3,3-d4 acid]. The chemical shifts and spectral assignments are provided in Table 2 (9,10). The effect of increasing concentrations of Al3+ on the... 

The last two criteria, (4) and (5), are the most unequivocal and powerful signs for the formation of the hydrogen bond. A A-H) and IRa H bCKA—H))/ IRa h(KA—H)) are the most important characteristics of H-bonding, its fingerprints or signature [33], say literally. Proton nuclear magnetic resonance ( H NMR) chemical shifts in the A H- -B hydrogen bond are shifted downfield compared to the monomer,... 

Fig. 8. Below 100 MHz proton nuclear magnetic resonance spectrum of the trimethyl-silyl region of 5-(+)-benzyl-a-OH.

Proton nuclear magnetic resonance ( H NMR) chemical shifts in the complex are significantly shifted downfield as compared to the monomer. 

The HT yield linearly correlated (Tang et al. 1971) with proton nuclear magnetic resonance (NMR) chemical shift, indicating the importance of electronic density effect in the reaction. 

Proton nuclear magnetic resonance (NMR) spectra (60 MHz) were recorded on a Varian EM-360L spectrometer. Carbon-13 (25 MHz) and 100 MHz proton NMR spectra were obtained on a Jeol JNM-FX-100 instrument. 1-H NMR (300 MHz) and 75 MHz 13-C spectra were determined on a Nicolet NT-300 instrument. Chemical shifts are given in parts per million (ppm) on a 6 scale downfield from tetramethylsilane (TMS) or solvent peaks [(dimethyl sulfoxide-d ) ... 

As with the convention for proton nuclear magnetic resonance, the cmr shifts are reported in parts per million (ppm) downfield from standard tetra-methylsilane (TMS). If the chemical shifts were originally reported relative to some other internal standard, these values were converted to a TMS reference for uniformity and ease of comparison. The equation used was Stms = cDcig + 77.0 = 192.4 - Scss = + 6.9. Deuteriochloroform... 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Proton chemical shift data from nuclear magnetic resonance has historically not been very informative because the methylene groups in the hydrocarbon chain are not easily differentiated. However, this can be turned to advantage if a polar group is present on the side chain causing the shift of adjacent hydrogens downfteld. High resolution C-nmr has been able to determine position and stereochemistry of double bonds in the fatty acid chain (62). Broad band nmr has also been shown useful for determination of soHd fat content. 

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for stmeture determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDCl ), 6 = 7.12, 7.34, 7.34, and 7.12 ppm. Coupling constants occur in well-defined ranges J2-3 = 4.9-5.8 ... 

If one wishes to obtain a fluorine NMR spectrum, one must of course first have access to a spectrometer with a probe that will allow observation of fluorine nuclei. Fortunately, most modern high field NMR spectrometers that are available in industrial and academic research laboratories today have this capability. Probably the most common NMR spectrometers in use today for taking routine NMR spectra are 300 MHz instruments, which measure proton spectra at 300 MHz, carbon spectra at 75.5 MHz and fluorine spectra at 282 MHz. Before obtaining and attempting to interpret fluorine NMR spectra, it would be advisable to become familiar with some of the fundamental concepts related to fluorine chemical shifts and spin-spin coupling constants that are presented in this book. There is also a very nice introduction to fluorine NMR by W. S. and M. L. Brey in the Encyclopedia of Nuclear Magnetic Resonance.1... 

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