Methanes, methyl substituted

In most of the acyclic examples of the di-7r-methane rearrangement studied, there has been methyl substitution on the central (C-3) atom. We should expect that electron-withdrawing substituents (relative to —CH3) on C-3 would lower the energy of the basis orbitals on C-3 and slow the transformation shown in the diagrams for schemes (3) and (4). 

Table II shows that the observed 29) shifts 8 (taken as positive downfield) show a degree of linear additivity in the methyl-substituted methanes, with a shortfall for neopentane. Table II shows also the division of the shielding into atom-plus-ligand diamagnetic and paramagnetic parts, relative to methane for which era is 295 ppm. The diamagnetic terms were calculated by Flygare s method 25). With each substitution of hydrogen by carbon, aa for the central carbon increases by 28 ppm but o-p increases by about 37 ppm, and the line moves 9 ppm downfield. Analogous relationships have been demonstrated for shielding in methyl-substituted NH3 and NH4+ 30). Table II shows that the shortfall at neopentane is in the paramagnetic term.

Shielding Terms for the Central Carbon in Methyl-Substituted Methanes ... 

Although the observed shifts are reasonably additive for methyl-substitution in methane, this is not true for other substituents, and the top half of Fig. 5 contains an up-dated version of the well-known plot 47) of shifts in substituted methanes against the number of substituents. The lower half of Fig. 6 shows that the large increase in with successive substitution accounts for most of the upheld turn of the plots. The residual shortfall in upAL increases with degree of substitution and... 

Ohmura, R. Matsuda, S. Takeya, S. Ebinuma, T. Narita, H. (2005c). Phase equilibrium for structure-H hydrates formed with methane and methyl-substituted cyclic ether. Int. J. Thermophysics, 26 (5), 1515-1523. 

Comparison of carbon-13 shifts of methyl phosphines and methyl substituted methanes... 

In spite of the large number of studies carried out on the DPM and the ODPM rearrangements since 1966, ten years elapsed before the reaction was extended to other 1,4-unsaturated systems, particularly to C-N double bond derivatives. The first example of a 1 -aza-di-Ti-methane (1-ADPM) rearrangement was reported by Nitta et al. in a study on the photoreactivity of the tricyclic oximes 5 [10]. Direct irradiation of compound 5a brought about the formation of the DPM product 6 and the 1-ADPM derivative 7a, in the first example of competition between these two processes. However, the methyl substituted derivative 5b yielded the 1-ADPM photoproduct 7b, exclusively (Sch. 4) [10a]. 

A series of polymerizations were performed to determine the effect of changing the diphenyl sulfone central group of the bis(phenoxy) and bis(phenylthio) monomers to a pentanedioxy group. The polymers obtained from methyl-substituted 1,5-bis(phenoxy)pentane contained structural units derived from proton transfer reactions [214]. Thus diphenyl methane, 1,2-diphenyl ethane, and benzyl chloride units were detected (Fig. 52). 

This general method of synthesis has been applied to each member of the methane series with the result that each hydrocarbon has been proven to be the methyl substitution product of another hydrocarbon containing one less carbon atom. We have then for the successive members of the series a continually elongating chain of carbon groups, each group being a residue of methane. For the first six members the formulas are as follows ... 

Methane, methyl chloride (CH3CI) and bromochloromethane (CH2ClBr) are each achiral. Bromochloromethane, however, has the property that further substitution of one of the two hydrogen atoms (by other than... 

That the Cp Ru fragment can also be used to break down carbon frameworks was shown by Chaudret et al., [27] who, using an example from steroid chemistry, achieved the elimination of methane from a methyl substituted cyclohexadiene with consequent aroma-tization. 

In all cases, the quantum yield of the molecular elimination of either methane or hydrogen is considered to be smaller than O.OS. Thus, the main primary processes involve either the a(C-C) or the P(C-H) bond ruptures. This observation differs from that made for ethylene, where at least 40% of the fragmentation involves the molecular elimination of hydrogen. May this behavior be linked to the differences observed in the absorption spectra At least, it may be said that well-defined absorption bands, one of which is probably Rydberg in nature, are observed in the ethylene spectrum. Conversely, the spectra of methyl substituted ethylenes are rather unstructured (1). The UV absorption spectrum of 1-butene is shown in Figure 4. We shall come back lat to diis point. 

Fig. 2.8 Acidities of some hydrocarbons, calculated by the CBS-4 method. For the methyl-substituted molecules the proton being removed is one on the methyl group. Methane is extremely weak as an acid and methylpyramidane is relatively strong...

It is interesting to examine the effect of a- and j5-methyl substitution on the acidity of methane. One a-methyl group decreases the acidity of methane, two a-methyl groups also decrease the acidity but by a smaller amount and the three a-methyl groups of the isobutane actually increase the acidity. (This last result is at odds with the theoretical results.)... 

Improvements in the Koch reaction were achieved by applying superacid systems as the acid catalyst (63). Triflic acid is especially useful because of its high acidity and the higher solubility of CO. Under superacidic conditions using HF-SbFs, alcohols, preferably secondary and tertiaiy alcohols, can be substituted for alkenes. Moreover, CO can react with monosubstituted methanes (methyl alcohol, dimethyl ether, methyl halides) to yield acetic acid or its derivatives. 

Shown in Table 1 [1] is a typical MTG hydrocarbon product analysis. The selectivity can of course be varied by changing reaction conditions, as shown later. The hydrocarbon distribution displays some noteworthy features little or no hydro n, methane, or ethane is produced the carbon number range is limited mainly to C ClO (it is fortuitous that ClO is also the normal end point of conventional gasoline) the fraction contains significant amounts of isobutane, which will be useful for alkylate synthesis under conditions in which light olefins are brought into balance with isobutane and the aromatics are nearly exclusively methyl substituted. 

In the absence of propane, the interaction between methane and zeolite Zn/HBEA yields methylzinc (ZnCHj) and methoxide (ZnOCHj) species and formate fragments, which undergo further conversion into acetaldehyde and acetic acid (Fig. 29D). In the presence of benzene, only the formation of the methoxide ZnOCH is observed, which is apparently not oxidized by oxygen of the defected ZnO structure (Fig. 29E). At 823 K, benzene is methylated by ZnOCHj, yielding methyl-substituted aromatics, namely, toluene and xylenes (Fig. 29F). It was thereby found that methane participated in the methane-propane co-aromatization reaction hy alkylating the aromatic compounds that resulted from propane, as is illustrated hy Scheme 7. 

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