Other Substituted Methanes

Other Substituted Methanes, The structures of several methane derivatives have been determined by a variety of techniques. From an analysis of the microwave spectra of ground-state and excited torsional states of a number of isotopic species of CHaSeH (1), the structural parameters of this 

The crystal structure of tetracyanomethane, C(CN)4, has been shown to be monoclinic, with space group Cc or C2/c and structural parameters a = 9.361(6), b = 8.851(5), c = 6.241(8) A p = 91.30(6)°. No crystallographic phase transitions were observed at normal pressures in a differential scanning calorimetry study from —150 to -fl60°C, which is the decomposition temperature of C(CN)4.  

A theoretical study of the topomerization of CHgOH [i.e. the conformational transformation from one Y conformation (8) into another] and the taut-omerization of this species into the methoxide anion, CHgOH CHjO, has been effected. The topomerization proceeds via the W conformation 

CH3NC — CH3CN has also been carried out, the principal object being the interpretation of the transition state. This particular tautomerism has also been the subject of an investigation in which experiments have been made to assess the importance of radical chain effects in the thermally induced reaction. It is concluded that there is no reason to doubt the fact that the isomerization of methyl isocyanide is an excellent test for the theory of unimolecular reactions. 

Thephenomenonof molecular reorientationalmotion in liquidCHsCN and has been investigated using i.r. and Raman spectroscopic 

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Figure 4.7 shows that any substituted methane, in which all four groups attached to the central carbon atom are different, as for example in CHFClBr, forms enantiomers. You can either use your imagination or constmct models of these enantiomers to show that you can superimpose the carbon atoms and any two of the other atoms, such as H and F, but the remaining two atoms. Cl and Br, cannot be superimposed. 

Various bromofluoromethanes have been described and proposed for use as fire extinguishing agents (qv). Two that have been recommended highly for this purpose are dibromo difluoromethane [75-61-6] CBr2p2, and bromotrifluoromethane [75-65-8], CBrF, (94). Bromochlorodifluoromethane [353-59-3], CBrClF2, is another fire extinguishing agent. These and similar substituted methanes are potentially useful for the synthesis of other halo—fluoro compounds. 

Secondly, we have labeled one of the substituted methanes 5-fluorochloro bromomethane and the other f -fluorochlorobromomethane. S (sinister, left) and R (rectus, right) are labels that are useful in designating the absolute configuration of chiral molecules in space. The rules for assigning S stereochemistry in one case and R stereochemistry in the other are somewhat complex but it doesn t matter, so never mind. The point is that we have a way of talking about the two possibilities. 

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... 

Addition to Other Unsaturated Molecules. When isocyanates are treated with alcohols, substituted methanes or carbamates are prepared (Reaction XIX). 

There are parallel achievements at the University of Pennsylvania, (Park etai, 1999 2000 2001 Gorte etai, 2000), using anodes with copper substituted for nickel to avoid carbon formation. The last two papers include the electrochemical oxidation of dry fuels other than methane, for example gasoline and diesel, the chemical exergy of which is difficult to calculate, since they are mixtures requiring separative work. 

The resting state (MMOoxd) is reduced back to the diferrous form to close the cycle. In addition to methane, many other substrates react with MMO. These include long-chain alkanes, alkenes, halogenated and other substituted alkanes, alkynes, sulfides, and others. 

Steacie comments that if the mechanism is correct in principle, this reaction must have an activation energy not greater than 5 kcal. This implies that Z)(G - Br) in carbon tetrabromide must be less than 50 kcal, which Steacie considers to be a surprisingly low result. It is, however, in line with other recent evidence on D C - Br) in other halogen substituted methanes. 

Brown ei al. now find that tri-/i-butylcarbinol is obtained in essentially quantitative yield by the reaction of tri-n-butylborane with chlorodifluoromethane (or other tri-substituted methanes) under the influence of lithium triethylcarboxide (equation 2). 

The smino acids used hy Blicke and Gould -were all secondary amines obtained by the addition of benzylamiue or alkyl amines to atropic acid or other substituted acrylic acids. The acid chloride salts v ore prepared by treatment with thionyl chloride, and after removing by-products the crude products were r cxed in bensene solution with excess dimethylaniline. The 1.8- and 1,4-disuhstituted azetidinones were isolated in yields of 40 80%, The benefioial influenoe of substitution was observed with the l-benzyl-S-methyl 4-phenyl- and l-benxyl-.S,3-dim thyl-4 phenyl-2-azetidinones, both of which were obtained in 90% yield. In an unsbooeasfu) attempt to prepare -aminodiasoketonea several of the acid chloride hydrochlorides were treated with diaxo-methane this reaction also fumishes the /9-laotams, although in rather low yield. 

Some other values of carbon-carbon coupling constants are given in Table 9. The data in Table 9 show that Jqc substituted cyclopropanes are proportional to in substituted methanes it is also apparent that the coupling constants increase with increasing substituent electronegativity. 

Abstract The activation of C-H bonds by oxidative addition in about 30 different substrates has been examined with three closely related metal species, [Tp RhL], where L = CNneopentyl, PMes, and P(OMe)3. Kinetic studies of the reductive elimination of R-H provided data to ascertain the relative metal-carbon bond strengths for a wide range of compounds. Trends in these bond strengths reveal that there are two classes of C-H substrates parent hydrocarbons and substituted methanes. DPT calculations are used to support the observed trends, and some generalizations are made by comparison to other metal systems. 

While all of the substrates discussed above are not shown in Fig. 2, the same analysis can be performed with all of them (alkynes, substituted methanes). One caveat that we encountered was that many of these substituted derivatives proved to be very stable. Loss of alkane from the n-pentyl hydride complex has a half-hfe of about an hour at 25°C. Methane loss from 3 has a half-life of about 5 h. Loss of benzene from 2, however, is extremely slow (months), and therefore, the rate of benzene reductive elimination at 25°C was determined by extrapolation from the rate at higher temperatures. The Eyring plot of hi( /T) vs. 1/T gave activation parameters for reductive elimination of benzene A// = 37.8 (1.1) kcal/mol and = 23 (3) e.u., which can be used to calculate the rate at other temperatures. As mentioned above, the substituted derivatives are much more stable. Reductive elimination of the alkynyl hydrides was examined at lOO C, as was the elimination of many of the substituted methyl derivatives. In these cases, the rate of benzene elimination was calculated from the Eyring parameters at the same temperature as that where the rate of reductive elimination was measured, so that the barriers could be directly compared as in Fig. 2. The determinatimi of AG° for all substrates allows Eq. 7 to be used to determine relative metal-carbon bond strengths for these compounds. Table 1 summarizes these data, giving A AG, AG°, and Drei(Rh-C) for all substrates. 

There are numerous examples of polar liquids at room temperature at least which exhibit Debye or nearly so behavior (in the sense of conformity to equation (35) over most of the frequency range of dispersion. Only a few of these are mentioned here others can be found for example in Bottcher-Bordewijk (48) and in the tables compiled by Buckley and Maryott (49). This is true of substituted methanes (50) (including methanol ) such as chloroform CHCl with = 5.7ps at 25 C. Even for these and other simple molecules there are small residual effects as indicated schematically in Figure 3(a). These seen as millimeter far infrared absorption are a resultant of inertial effects and Foley absorption variously attributed to librations coupling to translational modes and the subject of ot er contributions to these proceedings. 

Finally, the structure of various other substituted 2,2 -bithiophenes have also been investigated recently. This is particularly the case of 5,5 -dimethyl-2,2 -bithiophene and 5,5 -bis(trimethylsilyl)-2,2 -bithiophene [76], (3, 4,4, 5 -tetramethyl-2,2 -bithiophene-5-yl)-(3, 4,4, 5,5 -pentamethyl-2,2 -bithiophene-3-yl)methane [77], the solvatochromic 5-dimethylamino-5 -nitro-2,2 -bithiophene [78], and a bithiophene-derived annulene [79]. 

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