Nuclear magnetic resonance classes

No molecule is completely rigid and fixed. Molecules vibrate, parts of a molecule may rotate internally, weak bonds break and re-fonn. Nuclear magnetic resonance spectroscopy (NMR) is particularly well suited to observe an important class of these motions and rearrangements. An example is tire restricted rotation about bonds, which can cause dramatic effects in the NMR spectrum (figure B2.4.1). 

Physical Methods of Examination. Physical methods used to examine coals can be divided into two classes which, in the one case, yield information of a stmctural nature such as the size of the aromatic nuclei, ie, methods such as x-ray diffraction, molar refraction, and calorific value as a function of composition and in the other case indicate the fraction of carbon present in aromatic form, ie, methods such as ir and nuclear magnetic resonance spectroscopies, and density as a function of composition. Some methods used and types of information obtained from them are (41) ... 

No detailed description of H or 13C nuclear magnetic resonance (NMR) spectroscopy has been reported on this class of compound. A general description of the NMR spectra of compound 25 is given in the synthesis of a pyrrole <1998JOC9131>. 

Barlow, P. N., et al., Structure of the C3HC4 domain by IH-nuclear magnetic resonance spectroscopy. A new structural class of zinc-finger. / Mol Biol, 1994, 237(2), 201-11. 

In addition to being a fundamental tool for the structural characterization of almost all new members of this class of compounds, nuclear magnetic resonance (NMR) spectroscopy has also been central to a number of kinetic studies on the formation and reactivity of a selection of compounds in this class. As well as the more commonly reported H and NMR spectra, studies on other nuclei ( B, have provided key structural information for a... 

In an attempt to relate calculated results to experimental findings for monomeric, lignin model compounds, preliminary work has compared theoretically determined electron densities and chemical shifts reported from carbon-13 nuclear magnetic resonance spectroscopy (62). Although chemical shifts are a function of numerous factors, of which electron density is only one, both theoretical and empirical relationships of this nature have been explored for a variety of compound classes, and are reviewed by Ebra-heem and Webb (63), Martin et al. (64), Nelson and Williams (65), and Farnum (66). 

If the unknown, neutral, oxygen-containing compound does not give the class reactions for aldehydes, ketones, esters and anhydrides, it is probably either an alcohol or an ether. Alcohols are readily identified by the intense characteristic hydroxyl adsorption which occurs as a broad band in the infrared spectrum at 3600-3300 cm-1 (O—H str.). In the nuclear magnetic resonance spectrum, the adsorption by the proton in the hydroxyl group gives rise to a broad peak the chemical shift of which is rather variable the peak disappears on deuteration. 

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