Ionization potential oxetane

Recent 170 NMR studies have given us two values for the 170 chemical shifts in oxetane, -12.0 and -20.5 p.p.m., referenced to water (79BCJ3391, 80T3431). The rather wide band width may explain part of this apparent discrepancy. The 170 chemical shift of oxetane and other ethers was found to correlate with the reciprocal of their ionization potentials. 

The PE spectra of several oxetanes and related small ring compounds have received careful study. The first ionization potential for oxetane occurs at 7.65 eV as a sharp, adiabatic transition. This is at significantly lower potential than for oxirane (10.57 eV) or for acyclic ethers (dimethyl ether, 10.04 eV), showing the potential-lowering effect of the four-membered ring. This is seen also in azetidines and thietanes. 

The PE spectra for 2- and 3-oxetanone and 3-methyleneoxetane have also been measured and analyzed by means of comparison of the potentials with those calculated for the orbitals by both ab initio and semi-empirical methods. The first four ionization potentials and their assignments, as well as those for oxetane, are listed in Table 4. 

Table 4 Lowest Ionization Potentials (eV) and Assignments in PE Spectra of Oxetanes...

In the MS of oxetane the relative abundance of the ethylene radical ion is about eight times greater than that of the formaldehyde radical ion at the usual ionizing potential of 70 eV. However, 2,2-dimethyloxetane fragments much more to the radical ion of acetone... 

Both the reduction potential of 6-substitutcd cyclohex-2-enones and the ionization potential of the alkene control the product ratio of photocycloadducts vs. photoadducts on the one hand,90 and cyclobutane vs. oxetane formation, on the other91 (a similar dependence of the site of reaction as a function of the ionization potential of the alkene has been observed for 1,4-naphthoquinone92). 3- and 2-Alkynylcyclohex-2-enones on irradiation in the presence of alkenes afford both cyclobutane and cyclopentane derivatives.93-94 The regiochemistry of the photoadducts of simple cyclohex-2-enones to cycloalkenes seems to be dependent on the ring size of this latter species.95... 

Photooxetane formation is quite inefficient, a fact which usually points to the presence of an intermediate which can partially revert to ground state reactants. Cleavage of the diradical must be responsible for some of the inefficiency in oxetane formation 129>. However, in the past few years convincing evidence has appeared that a CT complex precedes the diradical iso.isi). The two most telling pieces of evidence are the relative reactivities of different alkenes 130> and the absence of any measurable secondary deuterium isotope effect on quenching rate constants 131>. Relative quenching rates of sterically un crowded olefins are proportional both to the ionization potentials of the donor olefins 130> and to the reduction potentials of the acceptor ketones 131>, as would be expected for a CT process. Inasmuch as n,n triplets resemble electron-deficient alkoxy radicals, such substituent effects would also be expected on direct radical addition of triplet ketone to olefin. However, radical addition would yield an inverse isotope effect (in, say, 2-butene-2,3-d2) and would be faster to 1,1-dialkylethylenes than to 1,2-dialkylethylenes, in contrast to the actual observations. 

Ionization potential of Continued) butenone, 123 cyclic diacetylenes, 305 cyclohexene, 48, 102 cis-cyclooctene, 102 Zraus -cyclooctene, 102 DABCO, 81 dimethyl ether, 123 ethylene, 80, 319 formaldehyde, 123, 319 hydrogen atom, 55, 75 methanol, 123 methyl acetate, 123 methyl acrylate, 123 nitrous oxide (N2O), 172 norbornadiene, 48 norbornene, 48 oxetane, 123 tetrahydrofuran, 123 trimethylamine, 81 water, 123... 

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