Cycloalkanes methylcyclohexane

Aware of the enhanced reactivity of trivalent [( ArO)3tacn)U] towards non-innocent solvents, such as ethers and chlorinated solvents, the reactivity of this molecule was challenged by exposure to more inert solvents like alkanes. Remarkably, recrystallization of 4 -bu u pentane solutions containing various cycloalkanes, i.e., methylcyclohexane, afforded the coordination of one cycloalkane molecule to the electron-rich U center (Scheme 4) (37). 

Cycloalkenes such as cyclohexene, 1-methylcyclohexene, cyclopentene, and nor-bornene are hydrosilylated with triethylsilane in the presence of aluminum chloride catalyst in methylene chloride at 0 °C or below to afford the corresponding hydrosilylated (triethylsilyl)cycloalkanes in 65-82% yields [Eq. (23)]. The reaction of 1-methylcyclohexene with triethylsilane at —20 °C occurs regio- and stereoselectively to give c/i-l-triethylsilyl-2-methylcyclohexane via a tra x-hydrosilylation pathway. Cycloalkenes having an alkyl group at the double-bonded carbon are more reactive than non-substituted compounds in Lewis acid-catalyzed hydrosilylations. ... 

Figure 3.8 Conversion with time in the hydrogenolysis of cycloalkanes (19Torr, 14.5 equiv.) catalyzed by (=SiO)2TaH (3) at 160°C under hydrogen (470Torr) cycloheptane ( ), methylcyclohexane ( ), cyclohexane ( ), methylcyclopentane (A) and cyclopentane (x).

The enthalpy of fomation of two such species has been measured, namely the cyclopropane and cycloheptane derivatives. The difference between the values for these two species, both as solids, is 238.1 kJmol . Is this difference plausible Consider the difference between the enthalpies of formation of the parent cycloalkanes as solids, 194 kJ mol . The ca 44 kJ mol discrepancy between these two differences seems rather large. However, there are idiosyncracies associated with the enthalpies of formation of compounds with three-membered rings and almost nothing is known at all about the thermochemistry of compounds with seven-membered rings. Rather, we merely note that a seemingly well-defined synthesis of cycloheptyl methyl ketone was shown later to result in a mixture of methyl methylcyclohexyl ketones, and superelectrophilic carbonylation of cycloheptane resulted in the same products as methylcyclohexane, namely esters of 1-methylcyclohexanecarboxylic acid. The difference between the enthalpies of formation of the unsubstituted alicyclic hydrocarbons cycloheptane and methylcyclohexane as solids is 33 kJmol . This alternative structural assignment hereby corrects for most of the above 44 kJ mol discrepancy in the enthalpies of formation of the two oximes. More thermochemical measurements are needed, of oximes and cycloheptanes alike. 

Class (1) reactions were observed in all four cycloalkanes. The highest rate constants were observed for reactions of cyclohexane hole with low-IP aromatic solutes, (3-4.5) x 10" sec at 25°C [75]. In these irreversible reactions, a solute radical cation is generated. Class (2) reactions were observed for reactants 1,1-dimethylcyclo-pentane, trans-l, 2-dimethylcyclopentane, and 2,3-dimethyl-pentane in cyclohexane [74], trans-dtcaXm, bicyclohexyl, and Ao-propylcyclohexane in methylcyclohexane [69], and benzene in cis-... 

Cycloalkanes possessing a tertiary carbon atom may be alkylated under conditions similar to those applied for the alkylation of isoalkanes. Methylcyclopentane and methylcyclohexane were studied most.5 Methylcyclopentane reacts with propylene and isobutylene in the presence of HF (23-25°C), and methylcyclohexane can also be reacted with isobutylene and 2-butene under the same conditions.20 Methylcyclopentane is alkylated with propylene in the presence of HBr—AlBr3 (—42°C) to produce l-ethyl-2-methylcyclohexane.21 C12H22 bicyclic compounds are also formed under alkylation conditions.21 22 Cyclohexane, in contrast, requires elevated temperature, and only strong catalysts are effective. HC1—AICI3 catalyzes the cyclohexane-ethylene reaction at 50-60°C to yield mainly dimethyl- and tetra-methylcyclohexanes (rather than mono- and diethylcyclohexanes). The relatively weak boron trifluoride, in turn, is not active in the alkylation of cyclohexane.23... 

Even condensed structures are awkward for cyclic molecules, and a streamlined way of drawing structures is often used in which cycloalkanes are represented by polygons. A triangle represents cyclopropane, a square represents cyclobutane, and so on. Carbon and hydrogen atoms aren t shown explicitly in these structures. A carbon atom is simply understood to be at every junction of lines, and the proper number of hydrogen atoms needed to give each carbon four bonds is supplied mentally. Methylcyclohexane, for instance, looks like this ... 

Cycloalkanes made up of a cycloalkane moiety linked to an alkane moiety are generally named in such a way that the cycloalkane is the parent system and the alkane moiety is considered to be an alkyl substituent. Therefore, the structure in following figure (a) is methylcyclohexane and not cyclohexylmethane. In it there is no need to number the cycloalkane ring when only one substituent is present. 

Other Cycloalkanes. Hydrogen chloride promoted monoethylation of other cycloparaffins (e.g., cyclopentane, methylcyclopentane and methylcyclohexane) and many paraffins (e.g., propane, isobutane, n -pentane, isopentane, 2,2-dimethylbutane, 2,3-dimethylbutane, n-heptane and 2,2,4-trimethylpentane). 

Similar to linear and branched alkanes, cycloalkanes also give rise to radical cations in zeolites, spontaneously or upon y-radiolysis. This brief discussion of selected examples is intended only to give a flavor of the work being done. Thus, a 13-line radical cation spectrum (a = 0.17 mT, g = 2.003) obtained upon incorporation of 1-methylcyclohexane, 43, into zeolites [71] was identified as 1,2-dimethylcyclopentene radical cation, 44 + (two sets of protons with hyperfine couphng constants in the ratio of ca 2 1 a = 1.67 mT, 2 CH3 a = 3.42 mT, 4H) [72]. The formation of 44 + was rationalized by protonation of the 3° carbon of 43, followed by loss of H2. Loss of a proton from a rearranged carbocation may generate 44, which is oxidized to 44 + by a Lewis site. 

We have already mentioned (Sec. 3.13) that petroleum from certain areas, (in particular California) is rich in cycloalkanes, known to the petroleum industry as naphthenes, Among these are cyclohexane, methylcyclohexane, methylcyclo-pentane, and 1,2-dimethylcyclopentane. 

EC>6-EC8 n-heptane, n-octane, some branched chain C6-C9 alkanes including trimethylpentanes, cyclohexane, methylcyclohexane, other cycloalkanes, some alkenes. 

The effect of phosgene upon a variety of alkanes (e.g. pentane, 2-methylbutane or hexane) or cycloalkanes e.g. cyclohexane or methylcyclohexane) in the presence of aluminium(III) chloride is to give symmetrical ketones no carboxylic acid chlorides were isolated from this reaction ... 

Upon sensitized irradiation, the triplet excited acyclic alkenes and large-ring cyc-loalkenes undergo E Z isomerization in both aprotic and protic media. Mediumring cycloalkanes cyclohexenes, cycloheptenes or cyclooctenes can, however, be protonated via the corresponding thermodynamically unstable (strained) /i-isomers formed initially by a Z —> E photoisomerization step (Section 6.1.1).662-664 For example, acid-catalysed irradiation of (Z)-l-methylcyclohexene (99) in the presence of /)-xylene as a triplet sensitizer in methanol affords the Markovnikov adduct 1-methoxy-l-methylcyclohexane (100) and the elimination product methylenecyclohexane (101), both in approximately 40% chemical yield (Scheme 6.41).671 The Zs-isomer intermediate exhibits extensive incorporation of deuterium in the presence of CH3OD. 

Data on rates of dehydrocyclization rD and cracking rc of n-heptane at 495°C and 14.6 atm are given in Table 5.2 for platinum-iridium on alumina and platinum-rhenium on alumina catalysts, and also for catalysts containing platinum or iridium alone on alumina (33). The rate rD refers to the rate of production of toluene and C7 cycloalkanes, the latter consisting primarily of methylcyclohexane and dimethylcyclopentanes. The rate of cracking is the rate of conversion of n-heptane to C6 and lower carbon number alkanes. 

Dehydrogenation of cycloalkanes such as cyclohexane, methylcyclohexane and decalin has been used for the storage and transportation of hydrogen fuel at an ambient temperature and pressure [2, 4, 14-20]. The advantages of cycloalkane dehydrogenation systems are as follows ... 

The cycloalkanes such as cyclohexane and decalin have a high hydrogen content and higher volume hydrogen capacity actually, hydrogen gas is stored by 530-710 times smaller volumes of organic hydrides such as methylcyclohexane and decalin. 

Hydrogen is stored efficiently by the exothermic hydrogenation of aromatic compounds, such as benzene, toluene and naphthalene, into the corresponding cycloalkanes at lower temperatures of 100-250 °C and relatively higher pressures of 1-10 bar, while hydrogen is preferably supplied by endothermic dehydrogenation (AHf= -65-68 kJ/mole H2) of cycloalkanes, such as cyclohexane, methylcyclohexane and decalin, by heating them above 250 °C ... 

We have found that the higher levels of conversion of cycloalkanes to arenes can be achieved with the iridium arsino pincer complex, IrH2(C5H3-2,6-(CH2AsBu 2)2) than are obtained with the analogous phosphino catalyst. However, inhibition of the arsino pincer catalyst is observed at the -20% dehydrogenation level for methylcyclohexane, decalin, and dicyclohexyl. 

SOLUTiON The molecular formula for a cycloalkane is C H2 . Because the molecular mass of both cycloalkanes is 98, their molecular formulas must be C7H14 (7 X 12 = 84 -h 14 = 98). Abase peak of 69 means the loss of an ethyl substituent (98 — 69 = 29), whereas a base peak of 83 means the loss of a methyl substituent (98 — 83 = 15). Because the cycloalkanes are known to be very stable, we can mle out cycloalkanes with three or four-membered rings. A seven-carbon cycloalkane with a base peak signifying the loss of an ethyl substituent must be ethylcyclopentane. A seven-carbon cycloalkane with a base peak signifying the loss of a methyl substituent must be methylcyclohexane. 

Low yields of the solvent Sj states. Radiolytic yields of the solvent Si states observed in the fast electron radiolysis of some alkanes (e.g., Cs-Cg paraffins) and cycloalkanes (e.g., C5-C7 cycloalkanes and methylcyclohexane)... 

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