Methylcyclopentyl

Redman, E.W. Morton, T.H. Product-Determining Steps in Gas-Phase Breasted Acid-Base Reactions. D rotonation of 1-Methylcyclopentyl Cation by Amine Bases. J. Am. Chem. Soc. 1986,108, 5701-5708. 

The reaction of a series of kinetically stabilized phosphaalkynes RC=P with complex Bu N=VCl3(DME) in the molar ratio 4 1 rather selectively afforded yellow azatetraphosphaquadricyclanes 62a-62e, in yields of 47-76%. Small amounts of the corresponding 1,3,5-triphosphinines (1-3%) were formed as by-products only with R = Pen, 1-methylcyclopentyl, and 1-methyIcyclohexyl. 

Answer The neopentyl system would migrate a methyl to give a tertiary carbocation. Isobutyl systems migrate an H to give the fert-butyl carbocation. The strained ring compound produces the 1-methylcyclopentyl carbocation. (Relief of severe... 

This structure has not yet been synthesized. However, many of the other methyl-substituted 1-methylcyclopentyl chlorides have been prepared and their rates of ethanolysis at 25 °C determined14 (4). 

It is worthwhile to mention that not only cyclopentyl but also the cyclohexyl type precursors gives the 1-methylcyclopentyl cation 36. This indicates that the cyclopentyl cation has higher stability, which causes isomerization of the secondary cyclohexyl cation to the tertiary methylcyclopentyl ion. 

Because of their crucial role in the ionization step, solvents have a profound effect on the rates of El reactions. These rates for a number of tertiary halides have been determined in a variety of solvents. For r-butyl chloride there are huge differences in the rates in water (log k = -. 54), ethanol (log k = -7.07), and diethyl ether (log k = — 2.1A)P Similarly, the rates of the El reaction of 1-methylcyclopentyl bromide range from 1 x 10 s in methanol to 2 x 10 s in hexane. Polar aprotic solvents such as DMSO (k = 2x lO s ) and acetonitrile (k = 9x 10 s ) are also conducive for ionization. The solvent properties that are most important are polarity and the ability to assist leaving group ionization. These, of course, are the same features that favor reactions, as we discussed in Section 3.8. 

On attempted vacuum-distillation of the 1-methylcyclopentyl hypochlorite obtained by chlorination of 1-methylcyclopentanol in alkaline solution, Cairns and Englund116 observed quantitative rearrangement of this material to 6-chloro-2-hexanone ... 

Entries 6-9 and 10-12 in Scheme 5.3 further illustrate the tendency for rearrangement to the most stable cation to occur. The tertiary 1-methylcyclopentyl cation is... 

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