Alternant Even Hydrocarbons

The systems without a cycle are represented here by the series of radical ions derived from polyenes 1—5) and a,co-diphenylpolyenes 6—10). With the former, the absorption curves are only available for the butadiene radical ions 58,57) whereas with the latter the situation is 

Among nonbenzenoid cyclic systems we mention radical ions derived from hydrocarbons 11—13. With diphenylene (the dibenzo derivative of 

For the l,3,7,9,13,15,19,21-octadehydro[24]annulene radical anion (72 in the formula only triple bonds are indicated) two groups of bands were observed in the regions at 15.6—17.8 and 21.3—25.6 K. The semiempirical calculations predict the first band in the infrared region at 2.6 followed by next bands at 8.6 and 10.8 AK. The electronic transition predicted at 18.5 AK can be assigned to the absorption at 15.6—17.8 AK and the next transitions at 21.6 and 

2 AK to the absorption at 21.3—25.6 AK. The assignment is based on the assumption that the nonplanar octadehydro[24]annulene becomes planar upon the uptake of one electron, as is the case with octatetraene and its dinegative ion. The presence of the triple bonds in 72 has been 

PES Cation Anion Cation ) Anion ) Cation4) Anion4) 

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Radicals with an odd number of electrons can be either uncharged odd hydrocarbons or radical ions of even hydrocarbons or systems derived from such hydrocarbons. Of special interest are the relationships that exist for radicals and radical ions of alternant hydrocarbons. 

This mechanism does not constitute a major reaction pathway for the anodic oxidation of alternant aromatic hydrocarbons (AAH) or alkyl-substituted AAH under common experimental conditions [12,16-19], but has been found to be operative, for example, for tetra-arylethylenes [20-23]. The difference in the reaction pattern of AAH and tetraarylethylenes is related to the rotational freedom around the central C-C bond experienced by the radical cations of the latter [24]. This results in a small or even negative difference between the standard potentials for the first and second one-electron transfer, E and E2, and, accordingly, the value of AT(j,spr [Eq. (15)] may take relatively large values. 

According to Coulson, The calculation of in this manner is too involved, so he has only illustrated for alternant (even cycle) hydrocarbons, which are given by... 

The dominance of the thermochemically more advantageous decomposition paths is illustrated in Fig. 45 which shows the mass spectrum of paraffin oil (a mixture of liquid paraffins, i.e. of h Mrocarbons of the structure CnH +a) The peculiar alternation of intensities is well-defined. The ions with an odd number of hydrogen atoms possess an even number of electrons and thus are not radical ions. The heat of their formation is lower than that of the ions with neighbouring masses and odd number of electrons, i.e. of radical ions that exhibit the less intense lines. This intensity alternation in hydrocarbon mass spectra, particularly evident for long-chain hydrocarbons, was first reported in [93]. 

Being an even, alternant, cyclic hydrocarbon benzene has orbitals which exhibit the pairing property as well as degeneracy. The energy levels are shown in Fig. 1.26. 

Alternatives to coal and hydrocarbon fuels as a source of power have been sought with increasing determination over the past three decades. One possibility is the Hydrogen Economy (p, 40), Another possibility, particularly for secondary, mobile sources of power, is the use of storage batteries. Indeed, electric vehicles were developed simultaneously with the first intemal-combustion-cngined vehicles, the first being made in 1888. In those days, over a century ago, electric vehicles were popular and sold well compared with the then noisy, inconvenient and rather unreliable peU ol-engined vehicles. In 1899 an electric car held the world land-speed record at 105 km per hour. In the early years of this century, taxis in New York, Boston and Berlin were mainly electric there were over 20000 electi ic vehicles in the USA and some 10000 cars and commercial vehicles in London. Even today (silent) battery-powered milk delivery vehicles are still operated in the UK. These use the traditional lead-sulfuric acid battery (p. 371), but this is extremely heavy and rather expensive. 

FIGURE 2.7 Energy levels in odd- and even-alternant hydrocarbons. The arrows represent electrons. The orbitals are shown as having different energies, but some may be degenerate. 

Recently, a nonempirical rr-electron SCF approach was reported and applied to interpretations of spectra of various conjugated hydrocarbon radicals (147). The greatest attention, however, has been paid to radical ions derived from even alternant hydrocarbons (10, 58-60, 63, 125, 135, 148-153). Here, numerous experimental material suitable for systematic testing of the MO methods has been accumulated. In particular, the following sources of experimental data should be mentioned Hamill and collaborators (24) prepared... 

Wastewaters containing chlorinated hydrocarbons (CHCs) are very toxic for aquatic system even at concentrations of ppm levels [1] thus, appropriate treatment technologies are required for processing them to non-toxic or more biologically amenable intermediates. Catalytic wet oxidation can offer an alternative approach to remove a variety of such toxic organic materials in wet streams. Numerous supported catalysts have been applied for the removal of aqueous organic wastes via heterogeneous wet catalysis [1,2]. 

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