Cyclopentane 2,3-dimethyl

H2O Water 100 CjHsN Pyridine 115.5 C7H14 1,1-Dimethyl- cyclopentane 87.8 Minimum b.p. 

Turova-Polyak and co-workers have carried out extensive studies of naphthene isomerization with AICI3, particularly of the substituted cyclopentanes. The conversion of mono- and disubstituted cyclopentanes to cyclohexanes was reported as an analytical technique for the determination of cyclopentanes in mixture with paraffins (411). Ethyl-cyclopentane at room temperature gave an 18-20% yield of cyclohexane derivatives (412). At 140-145°, an 85% yield of 1,3,5-trimethyl-cyclohexane was obtained. This work was also extended to 1,1-dimethyl-cyclopentane (410), up to 95% of which was converted to methyl-cyclohexane at 115°. Similar conversions of alkylated cyclopentanes were also reported by Shulkin and Plate (375). These researches parallel similar work done in the United States. 

Figure 3-13 compares the cis-trans isomers of but-2-ene with those of 1,2-dimethyl-cyclopentane. Make models of these compounds to convince yourself that cis- and trans-1,2-dimethylcyclopcntanc cannot interconvert by simple rotations about the bonds. 

In cyclic acetals, IX may be substituted at C2, C4, and C5. A tram arrangement of substituents at C4 and C5 will be more stable than a cis arrangement, as is clearly shown by the quantitative measurements on the cyclic 0-isopropylidene derivatives of erylhro- and threo-1,2-diphenyl-1,2-ethanediol, and the qualitative evidence given in Section V. The order of stability for isomeric derivatives with substituents at C2 and C4 (or C5) cannot be predicted by the method used for the 1,3-dimethyl-cyclopentanes, since that takes into account the puckering of the cyclopentane ring. 

According to quantum-chemical calculations the formation of the 2,4-dimethyl-cyclopentane intermediate is favored. However, Zambelli et al. reported that the formation of a metal-cyclopentane intermediate cannot explain the isotactic and syndiotactic polymerization on the base of the same type of mechanism. With some assumptions (for example, about the chirality of metal environment) the metal-cyclopentane mechanism can explain the formation of isotactic propylene. However, the driving force of the formation of the syndiotactic polymer is not evident at all. 

A fourth type of petroleum isomerization, which was commercialized on a small scale, involves the rearrangement of naphthenes. In the manufacture of toluene by dehydrogenation of methylcyclohexane, the toluene yield can be increased by isomerizing to methylcyclohexane the dimethyl-cyclopentanes also present in the naphtha feed. This type of reaction is also of interest in the manufacture of benzene from petroleum sources. 

Dimethyl-2-cyclopenten-l-one is a valuable starting material in terpenoid synthesis and in cases where a gem-dimethyl cyclopentane unit needs to be introduced. It is useful as a starting material in further functionalization. Its preparation by the method of Magnus is amenable to large scale synthesis. 

DIMETHYL-CYCLOPENTANE C-1,2-DIMETHYL-CYCLOPENTANE T-1,2-DIMETHYL-CYCLOPENTANE C-1,3-DIMETHYL-CYCLOPENTANE T-1,3-DIMETHYL-CYCLOPENTANE METHYLCYCLO-HEXANE HEPTANAL HEPTANE... 

Fig. 6. Carbon isotope compositions of total oils, Pr and Ph versus thermal maturity (Evolution Index) for oils from northeast Japan (Ishiwatari et aL, 2001). Data for total oils are quoted from Waseda (1993). Data for biodegraded oils are omitted. Definition of Evolution Index is a ratio of n-heptane to 1,3-dimethyl-cyclopentane (Hiratsuka, 1976). A thermal maturity index of L/(H L)-sterane (definition is given in the text) is quoted from Sakata et al. (1990) for comparison. Open circles total oils closed circles Pr and Ph (average values).

A plot of the resultant A O, against ring size is shown in Fig. 1, and from this it is seen that it is impossible (zI(t is positive) to polymerize cyclohexanes, methylcyclopentane, or 1,1-dimethyl-cyclopentane, at 25 C. Although in these cases the A S values are less negative than for the three- and four-membered ring polymerizations, the AH values are insufficiently negative to produce negative A O values. 

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