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1.3- Dehydro-5-adamantyl cation

The 2-methyl, 2-cyclopropyl and 2-phenyl substituted 8,9-dehydro-2-adamantyl cations 25 were prepared from their respective alcohols using fluorosulfuric acid in sulfuryl chloride fluoride at low temperatures (equation 27). The relative extent of charge delocalization in these cations was estimated by comparing their NMR spectra. The ions are nonequilibrating static cations, as shown by their proton NMR spectra56. [Pg.827]

The tertiary 2-methyl-8,9-dehydro-2-adamantyl cation 25, R = Me is stable up to 10 °C, and shows a much deshielded absorption for the cationic center (<5I3C 274.4), which is relatively shielded compared with the 2-methyl-2-adamantyl cation (<513C 323) showing some charge delocalization into the cyclopropane ring. The C8 and C9 carbons are also deshielded (<5I3C 100.7), comparable to other static cyclopropylcarbinyl cations. [Pg.827]

The l,2-dimethyl-8,9-dehydro-2-adamantyl cation 2656, as expected, is also a static cation and stable up to -10 °C. Its NMR behavior (<5I3C of C+ = 266.3) can be compared with the l,a,a-trimethylcyclopropylcarbinyl cation 20a (<513C of C+ = 276.6)54. The introduction of the 1-methyl group causes shielding of the cationic centers in both cases (the cationic center is shielded with respect to the demethylated analogue by 8 ppm in the former case, and it is shielded by 3.4 ppm in the latter case). [Pg.827]

Degenerate equilibration of the tertiary 2,8-dimethyl-8,9-dehydro-2-adamantyl cation 77 was observed between -26 °C and -128 °C. At -128 °C, the l3C NMR spectrum showed... [Pg.838]

The stability and symmetry of the 8,9-dehydro-2-adamantyl cation have been investigated and comparison has been made with the cyclopropyl car-binyl cation itself, 3S). For a complete discussion see Section V.B.l. [Pg.38]

The 8,9-dehydro-2-adamantyl cation (101) incorporates a cyclopropylcarbinyl system in the preferred bisected (97) conformation. As would be expected, then, 8,9-dehydro-2-adamantyl derivatives (e.g.102) are highly... [Pg.77]

Olah and coworkers NMR study of the 8,9-dehydro-2-adamantyl cation, obtained from the corresponding alcohol in superacidic medium, showed the equivalence of C2, C8 and C9 carbons ((5 C 157.0) in agreement with the conclusions of solvolytic studies Even at -120 °C the structure of the cation could not be frozen out to a static cation, showing the extremely fast equilibration of the threefold degenerate cyclopropylcarbinyl cation 74. An identical NMR spectrum was obtained from the ionization of the 2,5-dehydro-4-protoadamantanol, which prompted the suggestion of the intermediacy of the 2,5-dehydro-4-protoadamantyl cation 75. The ion rearranges to an ally lie cation 76 at -78 (equation 45). [Pg.838]

With the aim of studying a geometrically well-defined cyclopropylcarbinyl cation Baldwin and Foglesong (1968a) prepared the 8,9-dehydro-2-adamantyl 3,5-dinitrobenzoates [125 X = H, D or T]. The solvolysis of [125] in 60% aqueous acetone proceeded with considerable rate enhancement in comparison with 2-adamantyl tosylate. Scrambling of the label to the 8 and 9 positions in the solvolysis of [125 X = D] and [125 X = T] revealed a degenerate rearrangement (90) of the intermediate 8,9-dehydro-2-adamantyl cation [126]. [Pg.275]

Olah has discussed the extent of norbornyl cations and studied the l,2-diphenyl-2-norbomyl cation (102) by H and n.m.r. He concludes that it behaves as a rapidly equilibrating carbenium ion undergoing fast alkyl shift at -78°C. The cation (103) has also been prepared from several precursors in acidic media at —120 °C. Its spectra indicate rapid equilibration between carbenium forms. At — 60°C it rearranges to (104). The 8,9-dehydro-2-adamantyl cations (105 R = H or Me) have n.m.r. spectra which show that the tertiary cation is a static classical ion, whereas in the secondary case there is rapid equilibration making carbons 1, 8, and 9 equivalent. The analogous 2-substituted 2-adamantyl cations with R = Me, Et, Ph, OH, or halogen are simple ions which do not isomerize under the strong acid conditions used. " ... [Pg.360]


See other pages where 1.3- Dehydro-5-adamantyl cation is mentioned: [Pg.814]    [Pg.814]    [Pg.829]    [Pg.838]    [Pg.838]    [Pg.839]    [Pg.839]    [Pg.814]    [Pg.814]    [Pg.829]    [Pg.838]    [Pg.838]    [Pg.839]    [Pg.839]    [Pg.230]    [Pg.599]   
See also in sourсe #XX -- [ Pg.827 , Pg.828 , Pg.838 , Pg.839 ]

See also in sourсe #XX -- [ Pg.827 , Pg.828 , Pg.838 , Pg.839 ]




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Dehydro

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