Strained olefins ionization potential

The ionization potential, 8.69 eY, is lower than in the case of -cyclooctene (8.98 eV) or cyclohexene (9.12 eV), as expected. The highly strained anti-Bredt olefin, 11-bromo-e/ -9-chloro-7-ethoxybicyclo[5.3.1]undec-l(ll)ene has been synthesized and its struc-... 

Rates of phenyl azide addition have been correlated with ionization potentials for a number of strained olefins. The results show that about... 

In trying to make sense out of these diverse data on whether electron loss lessens strain, the simplest regularity arises from the observation of whether the electron is removed from the predominantly olefin or bicyclobutane fragment. This interesting ambiguity is resolved in the case of benzvalene to be from the former as shown by gas phase photo- and solution phase chemi-ionization . Moreover, to the extent that the electron is taken from a 2-butene type orbital, one may expect that ionization of naphthvalene (30) and pleiavalene (31) will also be from the 7r-system because the ionization potentials of o-xylene and 1,8-dimethylnaphthalene are still lower. This is confirmed experimentally . 

In many examples the reactivity has been discussed in terms of strain release. Whereas it is apparent that some strain is released in addition reactions, other factors have to be considered. Thus, a linear correlation between the rate of epoxidation and the ionization potential of bridgehead olefins has been observed (227). Other factors such as the polarizability and hyperpolarizability, which are associated with the outer region of the electronic structure of molecules as well as with intermolecular forces and chemical reactivity have not yet been considered (277). 

Novel photoadditions to benzene are reported in Scheme 67.261.412—414 In the low-yield addition of allenes the 1,4-mode of addition is favoured, which contrasts with the addition of simple mono-olefins where the 1,3-mode is favoured. Further study shows that the 1,3-mode of addition is facilitated by strained olefins, i.e. olefins of lower ionization potential. In the case of the olefin adducts the stereochemistry has not been rigorously defined. On treatment with base the allene adducts fail to isomerize to give semi-bullvalenes, but it has not been established whether this is due to kinetic or thermodynamic factors. 

---