Butane ionization potential

Fig. 23. Adiabatic ionization potentials for methane, ethane, propane, and butane arranged as an energy level diagram.

Fig. 5. Rate of H—D exchange versus ionization potential of alkanes and aromatic compounds 1 = methane 2 = ethane 3 = propane 4 = n-butane 5 = n-pentane 6 = n-hexane 7 = cyclopentane 8 = cyclohexane 9 = benzene 10 = naphthalene 11 = phenanthrene 12 = 2,2-dimethylbutane (see text) 13 = 1,1-dimethylpropy I benzene (see text) 14 = 2-methylpropane 15 = 2-methylbutane 16 = 2,2-dimethylpropane 17 = 2-methylpentane 18 = 3-methylpentane 19 = 2,3-dimethylbutane 20 = 2,2-dimethylbutane.

I11 AN without supporting electrolyte, the positive end of the potential window reaches +6 V vs Ag/Ag+, and the electrolytic oxidations of substances with high ionization potentials, including methane, butane, pentane, heptane, rare gases (Ar, Kr, Xe) and oxygen, can be observed [69 a]. In SO2 at -70°C and without supporting electrolyte, Cs+, Rb+, K+ and Na+ were oxidized at a platinum UME (10 pm diameter)... 

However, it is difficult to reconcile the observed relative reactivities of hydrocarbons with a mechanism involving electron transfer as the rate-determining process. For example, n-butane is more reactive than isobutane despite its higher ionization potential (see Table VII). Similarly, cyclohexane undergoes facile oxidation by Co(III) acetate under conditions in which benzene, which has a significantly lower ionization potential (Table VII), is completely inert. Perhaps the answer to these apparent anomalies is to be found in the reversibility of the electron transfer step. Thus, k-j may be much larger than k2 for substrates, such as benzene, that cannot form a stable radical by proton loss from the radical cation [Eqs. (224) and (225)]. With alkanes and alkyl-substituted arenes, on the other hand, proton loss in Eq. (225) is expected to be fast. 

As already mentioned, ionization potentials have often been correlated with electrochemical ones, most often with Evv Here one finds correlations covering both a limited range of compounds, such as aromatic hydrocarbons [(85), Pysh and Yang, 1964 (86), Neikam and Desmond, 1964] bicyclo[1.1.0]butane derivatives [(87), Gassman et al., 1979 ]2, and homoleptic alkylmetals [ (88), Klingler and Kochi, 1980] and a very extended range of different types of aliphatic and aromatic compounds [(89), Miller et al., 1972]. For the E°/IP set... 

Methane, n-butane, isobutane, and cyclohexane have strong C—H bonds (I>c—h > 390 kJ mol and high oxidation potentials (IP > 9.8 ev), and vigorous conditions are required to oxidize these hydrocarbons with inorganic oxidants. On the other hand, toluene and o-, m-, and p-xylenes have weaker C—H bonds ( >c h 355 kJ mol ) and lower ionization potentials (IP < 8.8 eV), and can be oxidized more readily. 

Acetonitrile has a very anodic decomposition potential. Exchange of the perchlorate anion against tetrafluoroborate or hexafluorophosphate shifts the anodic decomposition potential (ImAcm" ) of acetonitrile from 2.48 to 2.91 or 3.02 V vs Ag/Ag, respectively. In acetonitrile/TEABF4 some half-wave potentials have been determined to be 3.0 V for i-pentane, 3.01 V for 2-methylpentane, 3.28 V for 2,2-dimethyl-butane and >3.4V for n-octane, n-heptane and n-hexane. The half-wave potentials of some alkanes have also been obtained by the use of ultramicroelectrodes in acetonitrile without any supporting electrolyte the values range from 3.87 V for methane to 3.5 V for n-heptane vs Ag/Ag. These values correlate well with the ionization potentials of the alkanes". Controlled potential electrolyses were carried out on saturated solutions of four alkanes in acetonitrile 0.1 M TBABF4 to yield acetamidoalkanes (Table 5). ... 

According to the data presented, the value of the ionization potential (IP) for the transition states is correlated with the activation eneigy and increases as the number of alkyl substituents at the double bond grows. For ethylene of the transition state Ic the IP value amounts to 12.28 eV whereas this value of butane-2 is already 12.28 eV. The exception is the isobutylene the IP and A Gt 298 values of which are minimum in the considered alkene series. It is probably e qilained by F effect of two methyl substituents leading to a considerate distortion in electronic density of the double bond. 

Olivella, S. Sole, A. McAdoo, D.J. Griffin, L.L. Unimolecnlar Reactions of Ionized Alkanes Theoretical Study of the Potential Energy Surface for CH3 and CH4 Losses From Ionized Butane and Isohn-tane. J. Am. Chem. Soc. 1994, 94, 11078-11088. 

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