Chemical shifts methane protons

Empirical correlations between structure and proton chemical shift have been developed for common structural units. The earliest, called Shoolery s rule, provides the chemical shift of protons in a Y — CH2 — X group by adding substituent parameters A/ to the chemical shift of methane (see Table 3-1) ... 

The temperature of zeolite samples containing various adsorbed molecules was switched from room temperature to 500-600 K within 30-40 seconds by means of a laser beam. Catalytic n-alkane cracking and H-D exchange with deuterated cyclohexane were monitored by IH MAS NMR in time steps of down to one second. A two-dimensional representation of the chemical shift and the chemical reaction of the species will be given, allowing a good characterization of reaction steps. At low temperature a weak proton transfer without chemical reaction can be observed, whereas at 430 K and 530 K the proton transfer is accompanied, respectively, by an isomerization or a decomposition to methane and coke. In addition to the effect of high temperature, the laser radiation itself can force the conversion of alkanes to methane and coke. 

The progressive replacement of hydrogen with chlorine on a methane molecule moves the chemical shift to higher frequency (downfield) because of chlorine s ability to remove electron density from the remaining protons bO.23 for CH4,3.05 for CH Cl.5.30 for... 

A. Together with methane, the hydrocarbon adamantane (75), the parent structure of 74, has a tetrahedral skeleton. Therefore derivatives of adamantane that have four different substituents at the bridgehead positions should be chiral this has been demonstrated for 76 (see Hamill and McKervey31). It follows that in 74, Ha and Hb are enantiotopic, and indeed 74 has a plane of symmetry through C(l) and C(3). A parallel situation exists in ethanol, which has a plane of symmetry through two carbon atoms and oxygen. Although H and Hb in 74 are enantiotopic, the chemical shift difference between these protons is likely to be very small. 

Proton chemical shifts (in c./sec. at 60 Mc./sec.) of dilute solutions of methane in various solvents relative to external chloroform... 

The formula allows you to calculate the approximate chemical-shift values for protons ( H) based on methane (0.23 ppm). Although it is possible to calculate chemical shifts for any proton (methyl, methylene, or methine), agreement with actual experimental values is best with disubstituted compounds of the type X—CH2—Y or X—CH2 X. 

The deshielding of protons and carbon by substituents has given rise to attempts to predict the chemical shift by application of empirical additivity rules. While these can be useful, they are, at best, only approximate. Thus, as shown in Table 5.3 for the chlorinated derivatives of methane, there is not a simple incremental value to... 

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