Ionization potential dimethyl ether

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. 

Block et al.194 examined the effects of trimethylsilyl substitution on the first vertical ionization potentials by photoelectron and Penning ionization electron spectroscopy studies of a range of cyclic and noncyclic sulfides and ethers. It was shown that substitution of oxirane 218 with a trimethylsilyl substituent as in 219 lowered the ionization potential by 0.90 eV (20.8 kcal/mol), while similar substitution of dimethyl ether 220 in 221 lowered the ionization potential by 0.64 eV (14.8 kcal/mol). By comparison, the effects of silyl substitution on sulfur lone-pair ionization potentials was found to be smaller thus the ionization potential of dimethyl sulfide 222 is lowered by 0.37 eV upon trimethylsilyl substitution in 223, and the trimethylsilyl-substituted thiirane 225 is lowered by 0.59 eV relative to thiirane 224. The raising of the energy of the sulfur lone-pair electrons in the thiirane 225 is also apparent from its UV spectrum, where there is a bathochromic shift in the absorption maximum compared to the parent 224. 

Photoionization indicated an ionization potential of 10.565 eV, which is in excellent agreement with the value of 10.5 eV calculated from the UV spectrum. The oxiranes have higher ionization potentials than that observed for dimethyl ether (lO.OeV) this demonstrates the less effective nature of the delocalization of the 2p 7T-electron pair in the case of oxirane than in simple ethers. Support for this is provided by the experimental fact that the oxiranes exhibit a charge shift from the oxygen towards the carbon atoms, which may cause an increase in the ionization potential of the 2p tt-electron pair. 

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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