Tricyclobutonium cation

Calculate separate DE, valuep for the configurations (land II) of the proposed tricyclobutonium cation assuming that the CH carbon in each forms only localized cr bonds, that the C-C-C angles at the apex are 90°. and that the bond lengths are 1.54 A. 

Solvolytic studies provided the first structural indication for almost every carbocation-ic intermediate and the C4H,+ ion is no exception. Roberts observed that the solvolysis of cyclopropylcarbinyl or cyclobutyl systems and the diazotative deamination reactions of cyclopropylcarbinyl amine or cyclobutyl amine gave similar product mixtures consisting of cyclopropylcarbinyl, cyclobutyl and allylcarbinyl derivatives in essentially the same ratio1,2. A common cationic intermediate of C3v structure, the tricyclobutonium ion 1, was... 

J. D. Roberts,seems to have first used the term nonclassical ion when he proposed the tricyclobutonium ion structure for the cyclopropylcarbinyl cation. See J. D. Roberts and R. H. Mazur, J. Am. Chem. Soc. 73, 3542 (1951). Winstein referred to the nonclassical structure of norbornyl, cholesteryl, and 3-phenyl-2-butyl cations. See S. Winstein and D. 

Cyclobutyl- or cyclopropylcarbinyl chloride or the corresponding alcohols react with SbFj to give stable ion solutions with identical H- and C-nmr spectra. These spectra indicate either an ion with three-fold symmetry, the tricyclobutonium ion [32], or a set of rapidly equilibrating, less symmetrical ions with the same effective averaged symmetry. These include cyclopropylcarbinyl cation [33], bicyclobutonium ion [34] or bent cyclobutyl cations [35]. Theoretical calculations predict similar energies for [33]-[35], but indicate that [32] is less likely (Hehre and Hiberty, 1974 Hehre, 1975). Isotopic perturbation studies by Saunders and Siehl (1980) indicate that the... 

J. D. Roberts seem to have first used the term nonclassical ion when he proposed the tricyclobutonium structure for the cyclopropylcarbinyl cation [Roberts, J. D., Mazur,... 

The CD2-label ed cation C4H5D2 shows a temperature-dependent upheld shift for the nondeuteriated methylene carbons of 1.77 ppm ( — 135 C) to 1.24 ppm (— 107°C) (compared with the protio-ion), indicating a dehnite equilibrium isotope effect. A three-fold symmetrical static structure like the tricyclobutonium [135] is not consistent with this result and cannot be the main species present (Saunders and Siehl, 1980). 

Figure 10 Portion of the structure diagram for the C4H7 system showing only stable structures. The three-fold symmetry accounts for the scrambling of the three methylene carbon atoms via interconversion of the cyclopropylcarbinyl 1 and cyclobutyl 2 cations. The planar homoallyl structure 3 is obtainable from the same transition state for conversion of 1 to 2. The central structure 4 is a relatively high-energy trimethylene methane cation intermediate, incorrectly assigned a structure corresponding to tricyclobutonium ion in a mechanistic model of the scrambling of the methylenic carbons...

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