Hydrogen resonant frequency

Despite these simplifications, a typical or F NMR spectrum will nomially show many couplings. Figure BTl 1.9 is the NMR spectrum of propan-1-ol in a dilute solution where the exchange of OH hydrogens between molecules is slow. The underlymg frequency scale is included with the spectrum, in order to emphasize how the couplings are quantified. Conveniently, the shift order matches the chemical order of die atoms. The resonance frequencies of each of the 18 resolved peaks can be quantitatively explained by the four... 

Each hydrogen atom in a unique chemical environment is shielded differently from the external field and has a slightly different resonance frequency. The chemical shift in ppm, 5, is defined as... 

EPR spectrometers use radiation in the giga-hertz range (GHz is 109 Hz), and the most common type of spectrometer operates with radiation in the X-band of micro-waves (i.e., a frequency of circa 9-10 GHz). For a resonance frequency of 9.500 GHz (9500 MHz), and a g-value of 2.00232, the resonance field is 0.338987 tesla. The value ge = 2.00232 is a theoretical one calculated for a free unpaired electron in vacuo. Although this esoteric entity may perhaps not strike us as being of high (bio) chemical relevance, it is in fact the reference system of EPR spectroscopy, and thus of comparable importance as the chemical-shift position of the II line of tetra-methylsilane in NMR spectroscopy, or the reduction potential of the normal hydrogen electrode in electrochemistry. 

Nuclei are affected by the microenvironment around them. Electrons around the nuclei shield the magnetic field experienced by the nuclei. If the electrons are withdrawn, the nuclei will experience a stronger magnetic field and require more energy (higher resonance frequency) to flip the spins, and vice versa. For NMR, the hydrogen nuclei of a compound... 

Should the compound under investigation have labile hydrogens, H <- D exchanges can occur in certain solvents. These exchanges will cause modifications in the intensity and position of the corresponding signals. Solvent-solute associations often occur and their stability will vary with polarity. These associations can alter the resonant frequencies, thus the position, of the signals in the spectrum. Consequently, the sample concentration and solvent used must be provided with the correlation tables. 

The cobalt-59 NMR spectra of various Co(R2Dtc)3 complexes and of Co(RXant)3 have been reported. For B0 =450 cm-1 a linear correlation between the resonance frequency (p/) and the Tig - Aig absorption maximum is observed (430). In an electrochemical study, Toropova et al. (592) reported on the catalytic liberation of hydrogen in solutions of Co(R2 Dtc)2 complexes R2 = (hydroxyethyl)2, //-hydroxyethyl, carboxymethyl, etc.). The following mechanism was proposed for this very interesting reaction ... 

Recently, Li et al. [16] performed PFG-NMR experiments on oil-in D20 emulsions. D20, with similar chemical properties as H20, was chosen because the NMR resonance frequency of deuterium is quite different from that of hydrogen. Therefore they could select the experimental parameters so that only NMR signals from oil molecules are observed. In their calculations they assumed a log-normal distribution. Because of the very different diffusion coefficients of the two oils used, they were only able to obtain stable converged distribution parameters for the n-octane sample during the non-linear fitting procedure. 

In general, the resonant frequencies can be used to determine molecular structures. H resonances are fairly specific for the types of carbon they are attached to, and to a lesser extent to the adjacent carbons. These resonances may be split into multiples, as hydrogen nuclei can couple to other nearby hydrogen nuclei. The magnitude of the splittings, and the multiplicity, can be used to better determine the chemical structure in the vicinity of a given hydrogen. When all of the... 

The only exception to a single population of sorbent in a glassy polymer was observed in the water-cellulose acetate system (5 1, 52). In this system two resonance frequencies and two relaxation rates for water were observed. However, the two dynamic states of the water in this system are due to specific hydrogen bonding interactions rather than sorption in Langmuir type holes. 

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