Heptatrienyl radical

The same method was used to determine the electron affinities of pentadienyl radical (0.91 eV) and heptatrienyl radical (1.27 eV)35. The corresponding bond dissociation... 

Structure 13 below represents 8 as combination of a one-carbon radical and a hep-tatrienyl radical. The nonbonding orbital coefficients in the heptatrienyl radical are 0.5, so the resonance energy of 8, R(8), is given by... 

The transition state can be disconnected into the allyl and the heptatrienyl radicals. An analysis of the interaction of their nonbonding orbitals reveals two favorable contributions and one which is unfavorable. Consequently, the transition state is nonaro-matic and the reaction is not favored. 

Similar arguments can be used to predict the relative stabilities of the cyclo-heptatrienyl cation, radical, and anion. Removal of a hydrogen from cyclohepta-triene can generate the six-77-electron cation, the seven-77-electron radical, 01 the eight-77-elec iron anion (Figure 15.6). All three species again have numerous resonance forms, but HiickeTs rule predicts that only the six-7r-electron cyclohep-tatrienyl cation should be aromatic. The seven-77-electron cycloheptatrienyl radical and the eight-77-electron anion are antiaromatic. 

Problem 15.10 Show the relative energy levels of the seven n molecular orbitals of the cycle-heptatrienyl system. Indicate which of the seven orbitals are filled in the cation, radical, and anion, and account for the aromaticity of the cycloheptatrienyl cation. 

The hydrogen transfer energy (Table 2) for cycloheptatrienyl anion is very small, suggesting that it is essentially unstabilized. The same conclusion may be reached using the data in Table 6. Here, the formation of the anion is 23 kcal/mol less exothermic than for the heptatrienyl anion. The formation of the latter anion is 17 kcal/mol more exothermic than for the allyl anion, and if this ion has 10 kcal/mol stabilization, the heptatrienyl anion will be stabilized by about 25 kcal/mol and leads to the conclusion that there is no significant. stabilization or destabilization for the cycloheptatrienyl anion. This presumably is at least in part a result of the puckered geometry of the anion. The cycloheptatrienyl radical has some stabilization. 

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