Small-ring Compounds. XXIII. The Nature of the Intermediates in Carbonium Ion-type Interconversion Reactions of Cyclopropylcarbinyl, Cyclobutyl and Allylcarbinyl Derivatives^1a

Abstract

Fig. 3. This is a schematic representation based O I I [ivcrage R, values appearing iii 7 differerit rlironiatographic runs. I t is evident that the various antimycin A components were obtained in cliroiiiatographically homogeneous form. Further, from these results blastmycin appeared to consist mainly of antimycin A3 with minor contamination by the A4 component.Paper chromatogranis of the various antimycin complex preparations are also given in Fig. 3 . I t is apparent that the four antimycin preparations all contained at least the ill, An and A 3 components, although in somewhat varying proportions. Yirosin was similar in Composition but also contained a significant proportion of antimycin Aq. The other preparations may also have contained small amounts of A 4 as it certainly was present in the Harada sample but yet was not detected by the chromatogram.Infrared spectra of various preparations as shown in Fig 4 reveal extremely close similarity both of the individual components A1 and A3 to each other and to blastmycin and virosin. Antimycin A2 and the antimycin complex also gave essentially the same infrared spectrum. The differences are too slight to be of much aid in establishing differences in the chemical structure. Evi-dently, the components differ from each othcr only in the alkyl side chains of the neutral portioii of the molecule.3 Such a relationship is also suggested by the molecular formulas of AI, AB and A3 which differ among themselves only by the ey uivalen t of one to three methylene groups, The ultraviolet spectra of the individual components also were essentially identical.The infrared tracing of blastmycin offers further evidence of its very close similarity with antimycin; furthermore, its melting point was close to that of antimycin AB and the mixed melting point showed no depression. These data taken together with the above paper chromatographic results establish quite conclusively that the major coniponent of blastmycin is identical with antimycin AB and indicate that the minor component very probably is antimycin Ad.All three of the isolated antimycin A components showed neutral equivalents appreciably lower than theory for their most probable molecular formulas. This discrepancy may be attributable to partial cleavage of the alkali-sensitive bond of the antimycin A structure.13 The investigation of these and other aspects of the chemistry of antimycin A is being continued.Investigation of the extent of isotope-position rearrangement in carbonium ion-type reactions of I4C-labeled cyclopropylcarbinyl derivatives has revealed that the three methylene groups of the starting material achieve a striking degree of equivalence between reactants and products. These results, taken in conjunction with the abnormally large solvolytic reactivities oE cyclopropylcarbinyl and cyclobutyl halides and sulfonate esters, can best be accounted for by assuming rapid but not instantaneous equilibration of three isxneric rion-classical unsymmetrical "bicyclobutonium" ion intermediates.Considerable interest att...

Bicyclobutonium ion versus cyclopropylcarbinyl cation chemistry: the cycloaddition reaction with ethene in the dilute gas phase

“…The structures of the C 5 H 11 O adduct ions, as reflected in their CAD spectra, are significantly different, as established by a divergence angle of 11.0°(derived from data in Table 1). The difference is consistent with expectations that 3 is the reactant in reaction (7) and 4 is the major reactant in reaction (8). The difference may mask the lesser presence of 3 in the composition of the C 4 H 7 derived from cyclobutyl chloride.…”

“…The C 2 H 5 O ion of m/z 45 is also the predominant fragment ion (%34% total ion current, a reproducible difference from that of reaction with 3) generated from the methanol adduct formed in reaction (8). If the cyclobutyl precursor generates initially only 4, then 4 must react with methanol to produce an adduct ion possessing a cyclopropylcarbinyl moiety.…”

“…The components of such a mixture would then react with methanol as outlined in both reactions (7) and (8). As discussed earlier, 3 would react with methanol to produce an adduct ion that has a cyclopropylcarbinyl moiety and would decompose upon collisional activation to yield the C 2 H 5 O fragment ion at m/z 45 [reaction (11)].…”

“…The analogous reaction starting with cyclobutyl chloride gave similar products. 8 Brown 9 postulated that the cyclopropylcarbinyl cation is in rapid equilibrium with the classical cyclobutyl cation, both of which react with solvent to give products. In contrast, Roberts and co-workers, [10][11][12][13] posited that the observed products result from a common intermediate, the bicyclobutonium ion, 4, which is the prototypical 'non-classical' carbocation.…”

Quantum-mechanical calculations of the stabilities of fluxional isomers of C 4 H\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}\begin{equation*}{\mathrm{_{7}^{+}}}\end{equation*}\end{document} in solution

“…However, even the use of internuclear distances is not wholly satisfactory for defining structures of highly fluxional entities such as the C 4 H 7 ϩ (2). The conundrum of the structure(s) of the C 4 H 7 ϩ cation has been with us now for half a century (3)(4)(5)(6) and has even been used in undergraduate chemical education to demonstrate the use of quantum-calculation software (7). Despite this, the experimental evidence directed to defining the structure of C 4 H 7 ϩ is unconvincing to the extent that it is generally considered to be only consistent with the higher-level quantum calculations.…”