The structure of the stable, long-lived 2-norbornyl cation as well as those of the related 2-methyl-, 2ethyl-, and 2-phenylnorbornylcations were studied in SbF5-S02 (SOzCIF, SOIF,) and FS03H-SbFs-S02 (SOn-CIF) solution by 1H and 13C nmr and laser Raman spectroscopy. The "frozen out" 2-norbomyl cation displays, at -154" in SbF5-S02CIF-S02F2, lH and 13c nmr spectra compatible olily with a nonclassical structure. The norbornyl cation was found to be identical with corner-protonated nortricyclene and was thus shown to contain a pentacoordinated bridging carbon atom involved in three-center bond formation. The Raman spectrum of the norbornyl cation also indicates nortricyclene and not norbornane-type skeletal symmetry. Quenching in tertiary base at -78" yields nearly exclusively nortricyclene. The rate of the 3,2-and 6,1,2-hydrogen shifts and the corresponding activation parameters were measured by nmr temperature-dependence studies of the ions and are discussed. The tertiary 2-methyl-and 2-ethylnorbornyl cations show, based on the Raman spectra and the 1H and 13C nmr studies, structural correlations jndicative of partial 6,2-u delocalization without, however, a nortricyclenetype skeleton. Very little or no u delocalization is found in the basically classical 2-phenylnorbornyl cations. For comparison with 13C nmr spectra obtained for the norbornyl cation, we also studied the nmr spectra of the nonclassical 7-norbornenyl and 7-norbornadienyl cations. The close relationship of the bridging pentacoordinated carbon in these ions with that in the 2-norbornyl cation is evident. It is concluded that these studies give a definitive answer to the controversial question of the nature of the long-lived norbornyl cation showing without doubt that it is the u-delocalized, nonclassical ion. considerable effort has been directed in the past two A decades toward the elucidation of the structure of the 2-norbornyl and related cation^.^ In 1949 Winstein suggested the symmetrically bridged, nonclassical structure which is generally depicted as structure l.3a (We, however, prefer to leave out the third dashed line in representations of the nonclassical 2-norbornyl cation, as in lb, for reasons given in the subsequent discussion.) Winstein, Roberts, and numerous subsequent investigators have presented evidence supporting this conception. On the other hand, advanced the view that the ion is a classical, secondary carbonium ion which achieves pseudosymmetry via fast Wagner-Meerwein 1,2-alkyl rearrangements as depicted in 2.Kinetic data for solvolysis reactions give only information about the transition state preceding ion formation and subsequent solvent capture. While the transition state should reflect the structure of the ion intermediate such extrapolation has inevitably lent itself to varied interpretation.

The preparation of dialkylhalonium ions from alkyl halides and antimony pentafluoride (or fluoroantimonic acid) or by alkylation of alkyl halides with alkyl fluoroantimonates in S02 solution at low temperature is described. The structure of dialkylhalonium ions is based on their nmr ( and 18C), laser Raman, and ir spectroscopic studies. Isolation of dimethylhalonium fluoroantimonate salts (1-3) was also achieved. It is also shown that in methyl (ethyl) bromide-aluminum bromide complexes dimethyl-(diethyl-) bromonium bromoalumina tes play a significant role. The alkylating ability of dialkylhalonium ions in alkylation of aromatics and (35) G.

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was taken up in 2 ml of freshly distilled -pyrone (110°, 26 mm). 51 The flask was protected from the atmosphere (Drierite-KOH) and pyrolyzed for 75 min in an oil bath maintained at 145°. Aliquots were removed periodically, acidified, and subjected to analysis on a 6 ft X '/4 in. column of 10% DECS on Chromosorb W. No indene was observed.(B) The above procedure was repeated and aliquots of the gases from the reaction vessel were removed periodically during a 20min period and analyzed (Porapak Q) indicating a nitrogen-carbon dioxide ratio of 1:120.In the Presence of 1,2-Diazine. To 28 mg (0.21 mmol) of 9 and 160 mg (0.43 mmol) of 18-crown-6 ether in 2 ml of dry benzene was added 35 mg (0.88 mmol) of potassium hydride. The addition was carried out under nitrogen. After the bubbling ceased, the (51) . E.

Preparation of Solutions of Cations. Most of the ions discussed were prepared from carbinol precursors. Best results were obtained by freezing approximately 60 mg of the alcohol into the wall of a test tube containing about 1.5 ml of the acid solution at -78°. The alcohol is then gently washed into solution. Careful agitation at the start is usually required. Complete mixing is accomplished with a vortex mixer. Typical acid solutions were ~1:3 (v/v) SbFe-SCbClF and saturated solutions (prepared at -10°) of SbF5 in S02.Quenching of Solutions of Ions. About 0.3 g of precursor alcohol was ionized as usual at -78°. The solution was allowed to stand at this temperature for 3.0 hr, at which time pmr showed no precursor remaining. The solution was added dropwise to a rapidly stirred solution of 100 ml of ice-water containing 5.0 g of K2C03 and 25 ml of diethyl ether. The aqueous layer was repeatedly extracted with ether and reduced in volume. Glpc was generally carried out on a Perkin-Elmer Model 226 gas chromatograph using a 50 X 0.01 in. capillary polypropylene glycol "R" column at 60°. Products were identified by comparison with authentic samples. Ratios of cyclobutanol to cyclopropylcarbinol varied (see text).Nuclear Magnetic Resonance Spectra. Proton spectra were recorded at 60 and 100 MHz on Varían Associates Model A56-60A and HA-100 spectrometers. Capillary TMS was used as reference. 13C spectra were obtained by the indor method. The general technique employed has been described previously.46 We have since modified the instrumentation. The proton (monitoring) signal was obtained at 100 MHz with a Varían HA-100 spectrometer. The 25.1-MHz frequency was obtained from a Monsanto 3100 Digital Frequency Synthesizer. Frequency sweeping was accomplished by means of the voltage ramp of a C-1024 timeaveraging computer which in some cases was also used for signal accumulation by rapid (30-60 Hz sec-1), repetitive sweeping through the 25.1 MHz region. 13C shifts were calculated with respect to 13CS2.Negative shifts indicate resonances downfield from 1SCS2.