Nuclear magnetic resonance aromatic proton resonances

Nuclear Magnetic Resonance. The nmr spectmm of aromatic amines shows resonance attributable to the N—H protons and the protons of any A/-alkyl substituents that are present. The N—H protons usually absorb in the 5 3.6—4.7 range. The position of the resonance peak varies with the concentration of the amine and the nature of the solvent employed. In aromatic amines, the resonance associated with N—CH protons occurs near 5 3.0, somewhat further downfield than those in the aliphatic amines. 

Carborane, Bk>C2Hi2, is quite soluble in aromatic solvents and is sparingly soluble in aliphatic solvents. The infrared spectrum has been previously reported.25 The proton nuclear magnetic resonance spectrum of a chloroform-d3 solution of carborane contains a broad CH resonance at 6.46 t. 

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. 

Since the product slowly darkens on exposure to air, it should be stored under nitrogen in a refrigerator. The compound solidifies on cooling m.p. 16.0-16.5°. Nuclear magnetic resonance spectrum (neat, tetramethylsilane internal standard) singlets at d 7.00 (aromatic protons), 3.93 (CH2), and 2.24 p.p.m. (NH). 

Nuclear magnetic resonance has frequently been employed for general studies and for the structural studies of petroleum constituents (Bouquet and BaiUeul, 1982 Hasan et al., 1989). In fact, proton magnetic resonance (PMR) studies (along with infrared spectroscopic studies) were perhaps the first studies of the modem era that allowed stmctmal inferences to be made about the polynuclear aromatic systems that occm in the high-molecular-weight constituents of petroleum. 

Chaffee AL, Fookes GJR, Polycyclic aromatic hydrocarbons in Australian coals— III. Structural elucidation by proton nuclear magnetic resonance spectroscopy, Org Geochem 12 261—271, 1988. 

Fulvic and humic acids have been investigated with carbon-13 and proton nuclear magnetic resonance spectrometry, GC/MS, and IR spectroscopy. The fulvic and humic acids were found to be predominantly carboxylic and aromatic with a high proportion of 0- and Ji-substituted carbon atoms, although aliphatic ones were also observed. 

The structures of vanicosides A (1) and B (2) and hydropiperoside (3) were established primarily by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques and fast atom bombardment (FAB) mass spectrometry (MS).22 The presence of two different types of phenylpropanoid esters in 1 and 2 was established first through the proton (4H) NMR spectra which showed resonances for two different aromatic substitution patterns in the spectrum of each compound. Integration of the aromatic region defined these as three symmetrically substituted phenyl rings, due to three p-coumaryl moieties, and one 1,3,4-trisubstituted phenyl ring, due to a feruloyl ester. The presence of a sucrose backbone was established by two series of coupled protons between 3.2 and 5.7 ppm in the HNMR spectra, particularly the characteristic C-l (anomeric) and C-3 proton doublets... 

The simulated distillation data (Table V and Figures 2, 4, 6) and the FIA analyses of the distillates (Table II) were obtained by standard ASTM methods D2887 and D1319, respectively. The mass spectrometric analyses (MS) of the saturates fractions (Table VI) were obtained by an in-house method similar to that of Hood and O Neal (44). The aromatic fractions were analyzed by the proton nuclear magnetic resonance (NMR) method of Clutter et al. (45), and the results are reported in Tables VII and VIII. 

Figure 15.16. H Relaxation of 1-naphthol protons with increasing humic acid concentration at pH 7. All protons are observed to relax at a similar rate, suggesting a nonselective interaction between the protons of 1-naphthol and humic acid. Reprinted from Simpson, M. I, Simpson, A. J., and Hatcher, R G. (2004). Noncovalent interactions between aromatic compounds and dissolved humic acid examined by nuclear magnetic resonance spectroscopy. Environ. Toxi. Chem. 23, 355-362, with permission from the Society of Environmental Toxicology and Chemistry.

Mao, J. D., and Schmidt-Rohr, K. (2004a). Accurate quantification of aromaticity and non-protonated aromatic carbon fraction in natural organic matter by l3C sohd-state nuclear magnetic resonance. Environ. Sci. Technol. 38,2680-2684. 

Representative examples of ring proton and carbon chemical shifts of all known l,4-(oxa/thia)-2-azoles were reported in CHEC-II(1996). A special notice should be given for H and 13C nuclear magnetic resonance (NMR) spectra of both dithiazolium 5 (X = Y = S) and oxathiazolium salts 6 (X = 0 Y = S) and 7 (X = S Y = 0) <1996CHEC-II(4)489>. A S downfield shift for both 3-H and 5-H as well as C-2 and C-5 is correlated with a potential 7r-electron delocalization and thus the aromaticity of these ring systems <1996CHEC-II(4)498>. 

When using the thermal process for the production of SCT pitch, the temperature and time are important process parameters. The higher the temperature used, the higher is the aromaticity and condensation of the aromatic rings. The average carbon and proton distributions (determined by Nuclear Magnetic Resonance Spectroscopy) of SCT pitches prepared by thermal process at 390°C and 430°C are presented in Table III. 

The typical monocarboxylic acid p-ClCeH CH isCC H has been analyzed by proton nuclear magnetic resonance. The nuclear magnetic resonance spectra show that the chlorine substitution is more than 95% para, and that 1 to 2% of the aromatic rings carry no chlorine substituent (10). 

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