Carbonium ions phenyl, structure

Not enough is known for one to predict whether ionic or radical cleavage will occur. Many a-chloro and cc-bromo phenyl ketones are used as photoinitiators for polymerizations 52>, so they clearly produce radicals readily. Irradiation of chloroacetone in solution initiates the addition of CCI4 and thiols to olefins 197). Careful analysis of product structures suggests that only radical cleavage occurs. For example, in anisole the main product is orf o-methoxyphenylacetone. Radicals but not carbonium ions add preferentially ortho to monosubstituted benzenes. 

The biomimetic construction of piperidine skeletons from N-methylhomoallyl-amines is performed by means of the ruthenium-catalyzed oxidation and subsequent olefm-iminium ion cyclization reaction. trans-l-Phenyl-3-propyl-4-chloropiper-idine 57 ivas obtained from N-methyl-N-(3-heptenyl)aniline stereoselectively via 56 upon treatment ivith a 2 N HCI solution (Eq. 3.72). This cyclization is the first demonstration of biomimetic formation of piperidine structure using N-methyl group, and can be rationalized by assuming the formation of iminium ion 58 by protonation of the oxidation product 56, subsequent elimination of f-BuOOH, nucleophilic attack of an alkene, giving a carbonium ion, which is trapped with Cl nucleophile from the less hindered side. 

The summations in eq. fl7) are positive for any value of m and increase with iticreasing m. Although the sum in the denominator lacks three terms, due to the covalently bound chlorine atom, which are present in the numerator, the higher order of the three central carbon to phenyl bonds of the carbonium ion and the attendant increase in vibrational frequencies apparently more than compensates for this deficiency. Quantitative comparison of the data with the fundamental theory of equilibrium isotope effects requires a complete analysis of the infrared spectra of the two chlorides and the two carbonium ions as well as the assumption that the system can be treated as if it were gaseous. The infrared spectra of all the species, both covalent and ionic, of Table XI except those relating to the mono-p-methyl structures have been determined (98) and a preliminary analysis effected (99) but the spectra are very complex and identification of all the relevant frequencies has not yet been accomplished. A simplified treatment (90) is in accord with the qualitative considerations presented above, however. 

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