Trienyl cations

Sorensen and co-workers242 have studied the stereochemistry of ring closure of arylallyl cations to bicyclic trienyl cations. Similar studies on 1-phenylallyl cations have been carried out by Olah et al.225 Persistent polyenylic cations generated upon incorporation of cinnamyl alcohols in zeolitic matrix have been identified on the basis of IR and UV-visible spectroscopy 243... 

This in no way detracts from the proved ability of the cyclohepta-trienyl cation to oxidize reactive amines, and consequently there is always doubt as to the true nature of the reaction mechanism when tropylium ion initiates polymerization of N-vinylcarbazole. We have made a detailed kinetic study of this polymerization (34), using an adiabatic calorimetric technique. Some typical data are shown in Table VII. Initiation is instantaneous and complete, there is no termination, and kp is evaluated readily as 4.6 X 10+5M-1 sec. 1 at 0°C. with Ea = 6 kcal./mole. By comparing data for the ion pair dissociation constant of C7HT"SbCl 6 (Table I) with the catalyst concentrations employed (Table VII) it is apparent that free tropylium ions are the dominant initiating speices. It... 

Q Write an equation to show the fomiation of the cyclohepla-trienyl cation by addition of bromine to the hydrocarbon. Useciiriy arrows to illustrate the stabilization of the cation. 

As a hydride ion is removed from the —CH2— group of cycloheptatriene, a vacant p orbital is created, and the carbon atom becomes hybridized. The cation that results has seven overlapping p orbitals containing six delocalized is electrons. The cyclohepta trienyl cation is, therefore, an aromatic cation, and all of its hydrogen atoms should be equivalent again, this is exactly what we find experimentally. 

Problem 15.10 I Show the relative energy levels of the seven 77 molecular orbitals of the cvclohepta-trienyl system. Tel) which of the seven orbitals are filled in the cation, radical, and anion, and account for the aromaticity of the cycloheptatrienyl cation. 

M. Orda-Zgadzaj, V. Wendel, M. Fehlinger, B. Ziemer, W. Abraham, Inclusion of organic cations by calix[4]arenes bearing cyclohepta-2,4,6-trienyl substituents, Eur. J. Org. Chem., 2001, 1549-1561. 

---