Alkanes substituted

It can be seen from Table 4.78 that the a increments can be reasonably rationalized in terms of inductive effects (Pauling electronegativities), while the shielding of carbons y to the substituent is generally attributed to a steric polarization of the yC — H bond. Inductive and electric field effects contribute to the f) increments. As electric fields can be evaluated only in rare cases, no general trend for the [) effect has been recognized so far. Frequently, the a and increments depend on whether a substituent X is terminal (n) or central (iso). If available, the iso increments are also given in Table 4.78. 

The increments of Table 4.78 permit a prediction of carbon shifts in substituted alkanes. Thereby, they may provide an assignment aid which is particularly useful when proton decoupling experiments (off-resonance, gated, selective) and the application of modern pulse sequences fail because of equal multiplicities (( —CH2 —)n chains) or signal overcrowding in the i3C and iH NMR spectra. The practical use of the increments is illustrated for 1,4-dibromopentane and lysine. 

Significant differences between predicted and measured 13C chemical shifts as found for some of the lysine carbons indicate that shift increments are not additive when interactions between substituents are involved. Although deviations from increment additivity are frequently observed, the sequence of 13C signals can be qualitatively evaluated in many cases. 

The application of these increments is illustrated for l-frans-2-cis-3-trimethylcyclo-hexane and m-3-methylcyclohexanol (data from Table 4.24). 

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Name the compound as a cycloalkyl substituted alkane if the substituent has more carbons than the ring... 

In addition to these main results some others can be found in Polya s paper, notably the enumeration of doubly and multiply substituted alkanes. 

When there are many carbon atoms which might be asymmetrical, the solution is more complicated. Nevertheless, by methods that basically rely on Polya s Theorem, enumeration of compounds taking chirality into account can be carried out. For alkanes and mono-substituted alkanes see the paper [BalA76] for the chiral alkanes with some restrictions see [QuiL77,79]. See also [HarF75], [PalE77], and [WorNSl] for other problems in which chirality appears. 

Polya also obtained asymptotic estimates for a number of other problems, such as multiply-substituted alkanes, ethane derivatives, and cycloparaffins. 

The most stable conformation of a substituted alkane is generally a staggered one in which large groups have an anti relationship. The least stable conformation is generally an eclipsed one in which large groups are as close as possible. 

Count the number of carbon atoms in the ring and the number in the largest substituent chain, (f the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane. If the number of carbon atoms in the largest substituent is greater than the number in the ring, the compound is named as a cycloalkyl-substituted alkane. For example ... 

The product of substitution reactions of alkanes with the halogens is typically a complex mixture of haloalkanes (halogenated alkanes). One way to limit the production of the more highly substituted alkanes is to use a large excess of the alkane then most reactions take place with the original hydrocarbon rather than with any haloalkanes produced in the reaction. 

In another reductive coupling, substituted alkenes (CH2=CH Y Y = R, COOMe, OAc, CN, etc.) can be dimerized to substituted alkanes (CH3CHYCHYCH3) by photolysis in an H2 atmosphere, using Hg as a photosensitizer. Still another procedure involves palladium-catalyzed addition of vinylic halides to triple bonds to give 1,3-dienes. ... 

In aqueous DMF, the reaction can be applied to the formation of C-C bonds in a solid-phase synthesis with resin-bound iodobenzoates (Eq. 6.33).80 The reaction proceeds smoothly and leads to moderate to high yield of product under mild conditions. The optimal conditions involve the use of 9 1 mixture of DMF-water. Parsons investigated the viability of the aqueous Heck reactions under superheated conditions.81 A series of aromatic halides were coupled with styrenes under these conditions. The reaction proceeded to approximately the same degree at 400°C as at 260°C. Some 1,2-substituted alkanes can be used as alkene equivalents for the high-temperature Heck-type reaction in water.82... 

A corresponding correlation is obtained for the rate constants of a,a -phenyl substituted alkanes 26 (R1 = C6H5, R2 = H, R3 = alkyl) (see Fig. 1 )41). It has, however, a different slope and a different axis intercept. When both correlations are extrapolated to ESp = 0, a difference of about 16 kcal/mol in AG is found. This value is not unexpected because in the decomposition of a,a -phenyl substituted ethanes (Table 5, no. 22—27) resonance stabilized secondary benzyl radicals are formed. From Fig. 1 therefore a resonance energy of about 8 kcal/mol for a secondary benzyl radical is deduced. This is of the expected order of magnitude54. ... 

It has to be pointed out, however, that these considerations suffer somewhat from the fact that up to now it was necessary to calculate the strain energies of the phenyl substituted alkanes by a different force field40 than those of the alkanes39. ... 

The two main groups of silyl substituted alkane ligands HC(SiMe3)3 and HCH(SiMe3)2 demonstrate significantly different steric demands, and we will discuss the two groups of alkali metal complexes separately. Only select compounds will be discussed. 

The answer is d. (Hardman, pp 308-313.) Halothane is a substituted alkane general anesthetic. It undergoes significant metabolism in humans with about 20% of the absorbed dose recovered as metabolites. Halothane can cause postoperative jaundice and hepatic necrosis with repeated administration in rare instances. 

Studying Figures 18.1 and 18.2 may help you learn the naming of substituted alkanes. 

Oxiranes undergo ring opening with trialkylsilyl chlorides to yield trialkylsilyl chloroethyl ethers [51]. The reaction has been shown to be catalysed by tetra-n-butylammonium chloride, although most studies have used triphenylphosphine as the catalyst. Substituted oxiranes are cleaved by haloalkanes to yield the corresponding l-ch oro-2-aIkoxy-2-substituted alkanes [52] (see Section 9.3). 

Radical addition of dibromodifluoromethane to alkenes followed by sodium borohydride reduction is a convenient two-step method for the introduction of the difluoromethyl group.5 Either one or both carbon-bromine bonds in the intermediate dibromides may be reduced, depending on the reaction conditions. In the case of acyclic dibromodifluoromethane-alkene adducts, the reduction occurs regioselectively to yield the relatively inaccessible bromodifluoromethyl-substituted alkanes. The latter are potential building blocks for other fluorinated compounds. For example, they may be dehydrohalogenated to 1,1-difluoroalkenes an example of this methodology is illustrated in this synthesis of (3,3-difluoroallyl)trimethylsilane. 

Thermal cleavage of C—C bonds has been studied in cyclopropanes and cyclophanes, and particularly extensively in highly substituted alkanes. Riichardt and his school discovered a linear correlation between the experimental activation enthalpy for the homolysis of the weakest bond in overcrowded ethanes and the strain in the ground states of these molecules in accordance to MM2 calculations (284). 

Free electron pairs are a good source for an electron which is to be ejected and therefore, the IE of ethanol and dimethylether is lower than that of ethane. It has been shown that the IE of a poly-substituted alkane is almost the same as the IE of the structurally identical mono-substituted alkane which has the lowest value. [27] The other substituent, provided it is separated by at least two carbon atoms, exerts a very small effect upon the IE, e.g., the IE of dimethylsulfide, CH3SCH3, 8.7 eV, is almost the same as that of methionine, CH3SCH2CH2CH(NH2)COOH. Introduction of an oxygen decreases the IE less than nitrogen, sulfur or even selenium do, since these elements have lower electronegativities and thus, are even better sources of an electron. 

Svec, H.J. Junk, G.A. Electron-Impact Studies of Substituted Alkanes. J. Am. 

Haloalkanes can be regarded as substituted alkanes in which one or more of the hydrogen atoms is replaced by a halogen atom. They are named in a similar fashion to branched-chain alkanes with the halogen atoms treated like branches. For example, the anaesthetic halothane has the structure shown in the diagram and is called 2-bromo-2-chloro-l,l, 1-trifluoroethane. 

There are many other aromatic hydrocarbons, i.e. compounds like benzene, which contain rings of six carbon atoms stabilised by electron delocalisation. For example, if one of the hydrogen atoms in benzene is replaced by a methyl group, then a hydrocarbon called methylbenzene (or toluene) is formed. It has the structural formulae shown. Methylbenzene can be regarded as a substituted alkane. One of the hydrogen atoms in methane has been substituted by a or —group, which is known as a phenyl group. So an alternative name for methylbenzene is phenylmethane. Other examples of aromatic hydrocarbons include naphthalene and anthracene. 

Thiols, sulfldes, and disulfides are dissolved in a sufficiently pure solvent (in general, ethanol for nonpolar compounds and water for polar tw-substituted alkane thiols) and then applied onto the cleaned gold surface. 

In principle, the molar ratio of different thiols in a mixed SAM is the same as their original molar ratio in the solution which was used for the formation. In other words, for a mixture of two thiol compounds which does not show demixing tendencies (phase segregation), a random attachment of both compounds onto the surface can be assumed [16]. This observation offers the potential to mix a cw-substituted alkane thiol with short-chain nonsubstituted thiols. As the result, anchor molecules are available for which steric hindrance is minimized (cf. Fig. 3). 

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