Proton-carbon spin coupling constants

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... 

Usually, a careful analysis of the combination of fluorine, proton, and carbon NMR chemical shifts and spin-spin coupling constants will provide definitive information regarding the structure of disubstituted fluoroaromatics. 

D 1H-13C CT-HSQC/HMQC identifies proton-carbon spin pairs in both sugar and base. The constant time evolution removes the peak splitting due to 13C-13C coupling. The proton and carbon resonances are subsequently connected by... 

Some carbon-13-proton spin coupling constants of dimethyl N,N-dimethylaminomethylenemalonate were determined (90IZV356). 

As with pyrazoles, the introduction of the nitro group into the imidazole ring position 4(5) leads to an approximately 30 ppm lowfield shift of the tpxo-carbon signal resonance (Tables 3.6 and 3.10) [24, 321-329], Thus, the chemical shift of the carbon atom bonded to the N02 group (C-ipso) is 149.2 ppm, whereas that of neighboring carbon (C-5) is 119.8 ppm. In 1-substituted 4-nitroimidazoles (Table 3.11) the shifts of the same carbons are 146 1 and 122 2 ppm, while in 1-substituted 5-nitroimida-zoles they are 138 1 and 132 1 ppm, respectively (Table 3.12). All this may be indicative of the possible existence of 4(5)-nitroimidazole as a 4-nitro tautomer. Moreover, another support for the structure may be provided by comparison of the proton spin-spin coupling constants - J, 2J and 1/ Cl I-111) [321, 322, 330],... 

Chemical shifts of the methyl protons (t= 7.41-7.64) are in the sequence 3-methyl 6-methyl < 5-methyl 4-methyl and those of the methoxy group (t = 5.82-6.07) are in the sequence of 3-methoxy < 6-methoxy <4-methoxy. The spin-spin coupling constants are J= 5.3-6, J35 = 2.0-3.7, J3a = 0.5-1.0, J45 = 8.0-8.8, 46 = 0.7-1.0, and Jga = 5.8-7.0. Long-range coupling constants between methyl protons and protons attached to the ortho ring carbon are smaller than 1 cps. 

Aldehyde protons (RCHO) absorb near 10 5 in the Ml N MR spectrum and are very distinctive because no other absorptions occur in this region. The aldehyde proton shows spin-spin coupling with protons on the neighboring carbon, with coupling constant / 3 Hz, Acetaldehyde, tor example, shows a quartet at 9.8 5... 

Matsumori, N., Kanono, D., Murata, M., Nakamura, H., and Tachibana, K. (1999). Stereochemical determination of acyclic structures based on carbon-proton spin-coupling constants. A method of configuration analysis for natural products. J. Org. Chem. 64, 866-876. 

The spin-spin interaction of the protons of the CHj group in 4-RO-benzenium ions and that of the protons occupying the 2- and positions (see the spectrum of the 4-methoxybenzenium ion in Fig. 3) is fairly large. For methylbenzenium ions it is markedly weaker and does not display itself in the spectra. The spin-spin coupling constants of protons located at sp -hybridized carbons of hydroxybenzenium ions and their O-derivatives are also somewhat higher than those for methylbenzenium ions their values are close to those recorded for the respective cyclohexadienones Summarized in Table 12 are the PMR data on a number of halogen-substituted hydroxy- and methoxybenzenium ions. 

In Table 19 calculated (Equations 40) and observed H chemical shifts of allenes are summarized. There is an overall good agreement between predicted and experimental values. The results in Table 20 show that Equation 46 is suited for the description of one-bond carbon-proton spin-spin coupling constants of allenes. Only for the bromoallene 116 there is a larger deviation between the... 

In Table 30 a summary of one-bond CH and CC coupling constants of cumulenes is given. For comparisons also corresponding values for ethylene are listed. The one-bond carbon-proton spin-spin coupling constants of the methylene systems H2C=T in Table 30 may be related to the square of the carbon 25-hydrogen Is bond orders according to Equation 128 (/ = 0.9441). 

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