Isopentane ionization

McGuire, J.M. Munson, B. Comparison of Isopentane and Isobutane as Chemical Ionization Reagent Gases. Anal. Chem. 1985, 57, 680-683. 

Superacids were shown to have the ability to effect the protolytic ionization of a bonds to form carbocations even in the presence of benzene.190 The formed car-bocations then alkylate benzene to form alkylbenzenes. The alkylation reaction of benzene with Ci—C5 alkanes (methane, ethane, propane, butane, isobutane, isopentane) are accompanied by the usual acid-catalyzed side reactions (isomerization, disproportionation). Oxidative removal of hydrogen by SbF5 is the driving force of the reaction ... 

Pentane and isopentane are ionized under the same conditions to the ferf-amyl cation. w-Hexane 6 and the branched C6 isomers ionize in the same way to yield a mixture of the three tertiary hexyl ions [Eq. (5.3)] as shown by their 1H NMR spectra. 

Isopentane is the smallest alkane in the series, having primary, secondary, and tertiary hydrogens. Under similar conditions as propane and isobutane, isopentane was partially ionized in DF-SbF5 at — 10°C (10% conversion) the recovered 90% of alkane showed extensive deuterium/proton exchange (12 atom% of the primary, 16 atom% of the secondary, 19 atom% of the tertiary hydrogens were exchanged as expected in accord with their relative cr-basicity).61... 

The same phenomenon was observed61 with propane (Figure 5.6) and isopentane (Figure 5.7) above 20 mol% of SbF5, reversible protonation and protolytic ionization decrease rapidly whereas the conversion of the alkane with concomitant reduction of SbF5 increases. H-D exchange data observed in small alkanes are collected in Table 5.1. 

The details of the mechanism of decay of states in alkanes retain their interest. The effect of deuterium on fluorescence lifetimes has been discussed in terms of the theory of radiationless transitions. Analysis of fluorescence line shapes and Raman excitation profiles of tetradesmethyl-p-carotene in isopentane has been carried out at 190 and 230K . Solvation occurs over a time scale of about 100 fs whilst vibrational relaxation has a time scale of about 250 fs. The kinetics of the interaction of alcohols with the excited state of triethylamine shows involvement of a charge transfer exciplex . Ionizing radiation is a means of exciting saturated hydrocarbons and the complexity of three component systems containing saturated hydrocarbons, aromatic solvent, and fluorescent solute has been examined. ... 

FIGURE 9. Comparison of the observed ionization energies 7 of the C2s bands in the He(IIa) PE spectra of linear, branched and monocyclic hydrocarbons with the lowest eigenvalues (equation 38) obtained by diagonalizing the adjacency matrix A of the corresponding AR-models (cf equation 39). Normal alkanes C , n = 1 to 5, methane to pentane. Branched alkanes i-C = isobutane, 1-C5 = isopentane, neo-Cs = neopentane. Cycloalkanes C , n = 3 to 8, cyclopropane to cyclooctane... 

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