Carbonium pentyl

The difference in behaviour between pentyl and butyl cation systems (Figs. 3 and 4) has also been encountered in trapping experiments with carbonium ions, primarily formed from alkanes and SbFs, by CO (Hogeveen and Roobeek, 1972). In the case of n-butane the secondary butyloxocarbonium ion is the main product, whereas in the case of n-pentane only the tertiary pentyloxocarbonium ion is found. 

Seven isomeric pentyl fluorides, including neopeniyl fluoride, gave the same tertiary carbonium ion (i.e. dimethylethylcarbonium ion. Table 6). Thus, in the strongly acidic antimony pentafluoride, complete... 

Perdeuteriated isopropyl, t-butyl, and t-pentyl fluorides were prepared from the corresponding deuteriated alkyl chlorides (bromides) by halogen exchange. The perdeuteriated alkyl fluorides were then used in the formation of the deuteriated carbonium ions under similar conditions as those for the protium complexes. The resonance spectra were obtained at 9 2 Mc/s and the data are summarized in Table 7... 

Pillai and Pines (84) found that neopentyl alcohol, mixed with 10% by weight of piperidine and passed over alumina prepared from aluminum isopropoxide, yielded 2-methyl-l-butene and 2-methyl-2-butene, in a maximum ratio of 3, and small amounts of 1,1-dimethylcyclo-propane. However, lert-pentyl alcohol yielded these two olefins in a maximum ratio of only 1.4, and none of the cyclopropane was produced (Table VI). Because of these facts a carbonium ion mechanism which is applicable to ferf-pentyl alcohol is not adequate to explain the rearrangement taking place during the dehydration of neopentyl alcohol,... 

A polar-type transition state is also supported by the occurrence of Wagner-Meer-wein rearrangements accompanying the elimination of hydrogen chloride, from neo-pentyl - " - - , bornyl > andisobornylchlorides - ° In the case of neopentyl chloride the formation of 2-methylbut-l-ene and 2-methyl-but-2-ene has been explained in terms of a non-classical carbonium ion type transition state. 

This alkyl carbonium ion, an electrophile, attacks the electron rich aromatic ring to give the alkylbenzene. The fact that carbonium ions are involved means it is to be expected they would undergo rearrangement to the most stable carbonium ion. It is this rearrangement of carbonium ions that accounts for the production of tert-pentylbenzene as the major product in (a)-(d), In each case, the tert-pentyl CH,... 

The different nature of the intermediate in the dehydration of primary and tertiary alcohols, is substantiated by the contrasting dehydration behaviour of neopentyl and -pentyl alcohols . The carbonium ion mechanism for the tertiary alcohol leads only to 2-methyl-1-butene (57%) and 2-methyl-2-butene (42%), but neopentyl alcohol gives different proportions of these olefins (64-73% 23-32%) along with small amounts of 1,1-dimethylcyclopropane. These latter facts are accommodated better in terms of a concerted mechanism for the dehydration of neopentyl alcohol, viz-... 

The first report of a significant secondary isotope effect of any kind was that of Lewis and Boozer (6) on the decomposition of 2-pentyl chlorosulfite, which proceeds presumably via carbonium ion formation. 

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