Alkane Substitution Reactions

The results of kinetic studies suggest that alkane substitution reactions typically proceed by a radical chain mechanism (Section 13.9). The initiation step in the chlorination of methane is the dissociation of chlorine ... 

Tantalum hydride(s) also catalyzes the hydrogenolysis of cyclic alkanes (substituted or not) but the reachvity order decreases with the cycle size as cycloheptane > methylcyclohexane > cyclohexane > methylcyclopentane > cyclopentane for the latter no reaction is actually observed (Figure 3.8). Activity decreases with hme and becomes low after 20 h. 

A large number of 5-deazaflavins (32 R1, R2 = H, alkyl, aryl R3, R4 = H, Cl, NO2, OH 48 examples in all), have been prepared in good yields via condensation of 6-substituted aminouracils with o-halo-benzaldehydes in DMF under reflux. The mechanism shown in Scheme 14 was proposed for this reaction.138 Several bis(5-deazaflavin-10-yl)alkanes (33 n = 6, 8, 10, 12) have also been prepared via the same route using bis(uracil-6-ylamino)alkanes.138 By an analogous reaction the substituted quinolines (34a) and (34b) were obtained in 87% and 50% yield, respectively, from enaminones (35a X = Y = NMe Z = O) and (35b X = Y = CH2 Z = Me2) and pentafluorobenzaldehyde in glacial acetic acid at reflux.139... 

This reaction is much faster than the carbon-carbon cleavage in neopentane, despite the initial formation of secondary carbenium ions. Norbomane is also cleaved in a fast reaction, yielding substituted cyclopentyl ions. Thus, protonation of alkanes induces cleavage of the molecule by two competitive ways (i) protolysis of a C—H bond followed by /3-scission of the carbenium ions and (ii) direct protolysis of a C—C bond yielding a lower-molecular-weight alkane and a lower-molecular-weight carbenium ion. 

The concerted bimolecular /3-elimination reaction of substituted alkanes (X-Ca H2-Cp H2-...) has been studied using the semilocalized quantum chemical approach.3... 

Accordingly, we heated a mixture of ethylene, excess PCI3 and elemental phosphorus together in an autoclave at 200 - 250° for 4 - 6 hours. The yield of the desired 1,2-bis(dichlorophosphino)ethane, CI2PCH2CH2PCI2, was 70%. When we applied this reaction to substituted ethylenes, such as propylene, or 1-butene, we obtained the corresponding l,2-bis(dichlorophosphino)alkanes, but in lower yields 15,16) (chart II). 

The use of hermetically sealed pans gave valid data for only a few substances. It is dubious whether the data in Table 3-15 are true values of the activation energy and the frequency factor from pyrolysis reactions. For example, activation energy E for phenan-threne according to the literature is twice the value found by the experiment using sealed pans. Similarly, the value for tiiphenylmethane (E - 255 kJ/Mol) is markedly lower than the reference value E 347 kJ/Mol). However the values ascertained for the two methyl-pyrenes are in the order of magnitude of other alkane-substituted aromatics. 

Besides substitution reactions, alkanes also can undergo dehydrogenation reactions in which hydrogen atoms are removed and the product is an unsaturated hydrocarbon. For example, in the presence of a catalyst [chromium(lll) oxide] at high temperatures, ethane can be dehydrogenated, yielding ethylene, C2H4. 

Distinguish between substitution and addition reactions. Give an example of each type of reaction. Alkanes and aromatics are fairly stable compounds. To make them... 

What are alkane substitution reactions Provide an example. 

What are the products of this alkane substitution reaction (Assume monosubstitution.)... 

In these reactions, RhuA was the most versatile aldolase, accepting both linear and branched C-a-substituted N-Cbz-aminoaldehydes, while FucA tolerated only C-a hnear alkane substitutions. Aware of the importance of the reaction medium, the reactions were assayed in both highly concentrated gel emulsions [17] and 1 4 N,N -dimethylformamide (DMF)/water mixtures. In this case, the 1 4 DMF/water mixtures was the reaction medium of choice providing the best conversions especially for stericaUy more demanding branched alkyl substituents [16]. 

This is an example of a substitution reaction. A substitution reaction is a reaction in which a part of the reacting molecule is substituted for an H atom on a hydrocarbon or hydrocarbon group. Ail of the H atoms of an alkane may undergo substitution, leading to a mixture of products. 

Kinetic studies suggest that alkane substitution reactions such as the one above proceed by a... 

In addition to combustion reactions, alkanes also undergo substitutionTeactions, in which one or more hydrogen atoms on an alkane are replaced by one or more other atoms. The most common substitution reaction is halogen substitution (also referred to as halogena-tion). For example, methane can react with chlorine gas in the presence of heat or light to form chloromethane. 

Classify each organic reaction as combustion, alkane substitution, alkene addition or hydrogenation, aromatic substitution, or alcohol substitution, elimination, or oxidation. 

Radical Reactkms.— The reaction of a-chloro ethers with zinc in the presence of thiophen yields di-2-thienyl alkanes (106). Photolysis of 3-iodopyridine in the presence of thiophen yields a mixture of 3-(2-thienyl)-pyridine and 3-(3-thienyl)pyridine in a 7 1 ratio. The synthesis and rate of decomposition of 2- and 3-thenoyl peroxides and of mixed thenoylfuroyl peroxides have been described. " Aryl 2-thenoates were obtained in high yields by the reaction of substituted benzenes with 2-thenoyl peroxide in the... 

Sulfonic acids may be hydrolytically cleaved, using high temperatures and pressures, to drive the reaction to completion. As would be expected, each sulfonic acid has its own unique hydrolytic desulfonation temperature. Lower alkane sulfonic acids possess excellent hydrolytic stability, as compared to aromatic sulfonic acids which ate readily hydrolyzed. Flydrolytic desulfonation finds use in the separation of isomers of xylene sulfonic acids and other substituted mono-, di-, and polysulfonic acids. 

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