Cyclo-alkanes

The estimates of the RSE for small cyclic alkanes, cyclo-olefins, and cyclic ethers using all three reactions are listed in Table 3.21. The failure of the isodesmotic reaction is readily apparent by examining the RSE of the cyclic alkanes. For the rings having five or more carbon atoms, the isodesmic method predicts that there is no strain energy. Rather, it predicts that these cyclic species are more stable than their acyclic counterparts. The homodesmotic and GE reactions, which are identical for the cyclic alkanes, provide RSEs in excellent agreement with CRSE estimates. 

The conversions of n-alkanes, cyclo-alkanes and their mixtures over PtAJSY zeolites imder vapor phase reaction were successfully modeled using independently determined adsorption equilibria and fundamental reaction networks based on allQ lcarbenium ion chemistry [9-12]. In these models, the intrinsic reaction rate of an individual reaction step... 

The solubility of individual hydrocarbons in pure water at 25 °C, as summarized by Tissot and Welte (1984) is given in Table 3.3. Table 3.3 indicates that there is a marked decrease in solubility with an increase in molecular weight (carbon number) for each class of hydrocarbons (alkanes, cyclo-alkanes, aromatics). It also shows that aromatics are more soluble than alkanes for a given carbon number. Polar heterocompounds (organic acids or alcohols) are more water soluble than the corresponding hydrocarbon with the same carbon number (Tissot and Welte, 1984). The hydrocarbon solubilities in water are influenced by temperature, salinity and pressure. 

Hydrocarbons consist of carbon and hydrogen. The carbon atom has four bonds while hydrogen has one bond. Depending on the molecular structure, different series can be distinguished alkanes, cyclo-alkanes, and aromatics. They are all inflammable. Skin contact and inhalation are to be avoided. 

As you can see cycloalkanes are named under the lUPAC system by adding the prefix cyclo to the name of the unbranched alkane with the same number of carbons as the ring Substituent groups are identified m fhe usual way Their posifions are specified by numbering fhe carbon atoms of fhe ring m fhe direction fhaf gives fhe lowesf num ber to fhe subsfifuenfs af fhe firsf pomf of difference... 

In this chapter we 11 examine the conformations of various alkanes and cyclo alkanes focusing most of our attention on three of them ethane butane and cyclo hexane A detailed study of even these three will take us a long way toward understanding the mam ideas of conformational analysis... 

Monocyclic Aliphatic Hydrocarbons. Monocyclic aliphatic hydrocarbons (with no side chains) are named by prefixing cyclo- to the name of the corresponding open-chain hydrocarbon having the same number of carbon atoms as the ring. Radicals are formed as with the alkanes, alkenes, and alkynes. Examples ... 

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

Thermal rearrangement of trans-l,2-dibromo compounds is known in the literature (refs. 6-10). In all case studies only one pair of bromine in each organic molecular was studied. Bellucci (ref. 10), for example, studied the kinetics of such trans-l,2-cyclo alkanes as cyclopentane, hexane, octane, etc. The intermediates suggested as an explanation for the experimental results are bromonium bromide I in polar solvents and four center transition state II in non-polar solvents. 

RoCek et al. have also measured rate coefficients for a series of cyclo-alkanes, (CH2) (/i = 4 to 14), and find the analogue of kcHj in equation (25) to fluctuate with ring size in a manner corresponding exactly to the enthalpy of combustion of the cycloalkane concerned per methylene group, provided n is greater than five, i.e. there exists a direct correlation between reactivity and thermochemical strain. 

In yet another version of adopting a biphase system, oxidation of alkanes with rert-butyl hydroperoxide has been conducted with an aqueous phase. Launay et al. (1998) have developed an efficient and highly selective conversion of cyclo-octane to cyclo-octanone using Ru colloidial particles formed in situ from RuCli. 5H2O. The aqueous phase can be recycled. 

Chemical catalysts for transfer hydrogenation have been known for many decades [2e]. The most commonly used are heterogeneous catalysts such as Pd/C, or Raney Ni, which are able to mediate for example the reduction of alkenes by dehydrogenation of an alkane present in high concentration. Cyclohexene, cyclo-hexadiene and dihydronaphthalene are commonly used as hydrogen donors since the byproducts are aromatic and therefore more difficult to reduce. The heterogeneous reaction is useful for simple non-chiral reductions, but attempts at the enantioselective reaction have failed because the mechanism seems to occur via a radical (two-proton and two-electron) mechanism that makes it unsuitable for enantioselective reactions [2 c]. 

Stepwise Cg dehydrocyclization (aromatization) involving the gradual loss of hydrogen atoms from an alkane followed by a triene - cyclo-hexadiene ring closure step 20, 21). This can be ... 

Protonation of alkenes, cycloalkanes and alkanes lead to the formation of carbe-nium ions, carbonium ions and protonated cyclopropane rings (also called cyclo-... 

More recently, the same principle was applied by the same authors to cyclic alkanes for catalytic ring expansion, contraction and metathesis-polymerization (Scheme 13.24) [44]. By using the tandem dehydrogenation-olefin metathesis system shown in Scheme 13.23, it was possible to achieve a metathesis-cyclooligomerization of COA and cyclodecane (CDA). This afforded cycloalkanes with different carbon numbers, predominantly multiples of the substrate carbon number the major products were dimers, with successively smaller proportions of higher cyclo-oligomers and polymers. 

A study of the stoichiometric cyclopentane reaction over Ta-H has revealed that tantalum hydride very easily achvates cyclopentane, forming the corresponding cyclopentyl derivative. However, the latter is very quickly transformed into a cyclo-pentadienyl compound, as shown by NMR and EXAFS studies. This cyclopenta-dienyl derivative presents no achvity in alkane hydrogenolysis ... 

K[Ru(0)(PDTA)].3Hj0 and Ru(0)(HEDTA) (PDTA=(propylenediaminetetra-acetate) -) are made by oxidation of K[Ru "Cl(PDTA.H)] or K[Ru" Cl(EDTA.H)] with PhIO electronic and ESR spectra were recorded. Rates and activation energies for epoxidation by stoich. Ru(0)(PDTA)] or Ru(0)(HEDTA)/water-dioxane of cyclo-alkanes were measured, as were those for oxidation of cyclohexane to cyclohexanol and cyclohexanone [632],... 

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