Cis-l,3-Dimethylcyclopentane

Two types of substrate probe, cis- and trans-l,3-dimethylcyclopentane and ethyl- and 2-propylcyclopropane, were used to shed light on mechanishc details of the hydroxylahon step [30]. In the use of the first two probes, the participation of Ti—OOH species in a concerted mechanism would predict either the retention or the inversion of configurahon at the chiral center, while the stereochemistry of a homolytic mechanism would be determined by the compehhon between the epimerization of the transient terhary carbon radical and C—O formation (Scheme... 

Scheme 18.1 Hydroxylation of sterically pure cis- and trans-l, 3-dimethylcyclopentane.

Hydrogen can add to the double bond of 1,4-dimethylcyclopentene either from the same side as the C-4 methyl group or from the opposite side. The two possible products are cis- and trans-l, 3-dimethylcyclopentane. 

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-... 

For example, Kunitake used the shifts on going from a trans-to a ciA-l,2-dimethylcyclopentane as representative of that which would occur in an analogous 2,3-dimethylsuccinic anhydride. Thus he estimated a shift of -5.1 ppm for C-2 (and C-3) and -2.1 ppm for the carbonyl carbon. We found that the actual shifts on going from trans- to cis-2,3-dimethylsuccinic anhydride are -4.1 ppm (C-2 and C-3) and +1.1 ppm (carbonyls). 

Figure 3-13 compares the cis-trans isomers of 2-butene with those of 1,2-dimethylcyclopentane. Make models of these compounds to convince yourself that cis- and rmn5-l,2-dimethylcyclopentane cannot interconvert by simple rotations about the bonds. 

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