Butanal radical cation

Spin density surface for butanal radical cation shows location of unpaired electron. 

Electrostatic potential map for butanal radical cation shows most positively-charged regions (in blue) and less positively-charged regions (in red). 

Use geometries, electrostatic potential maps and spin densities to help you draw Lewis structures for butanal radical cation, the transition state and product. Where is the positive charge and the unpaired electron in each Is the positive charge (the unpaired electron) more or less delocalized in the transition state than in the reactant In the product ... 

Figure 6.9. Top to bottom Two possible Jahn-Teller distorted geometries for the methane radical cation and calculated geometry for its energy minimum schematic representation of the SOMO for ethane radical cation SOMOs of three different propane radical cations observed by ESR the SOMO of butane radical cation and SOMOs for two conformers of pentane radical cation.

Table 5. Isotropic hyperfine coupling constants (Gauss) of the bicyclo[1.1.0]butane radical cation.

The data suggest that much of the unpaired electron density in the bicyclo[1.1.0] butane radical cation is associated with the two bridgehead carbon atoms, but that in the l,3-dimethylbicyclo[1.1.0]butane radical cation about 15% of the unpaired electron density is associated with the methyl substituents at these positions. 

Isotropic value. Maximum value, ay. ) Extrapolated value. ) MINDO/3 calculations. Thermal decomposition of butane radical cation and D-labeUed derivatives in CF2CICFCI2 at 100 K. ... 

Figure 11. Density difference plots for some hydrocarbon radical cations. The compounds are A cyclopropane, B bicydo[1.1.0]butane, C bicycio[l.l,l]penlane, and D [l.l.l]propellane (reproduced from ref 108 with the permission of the American Chemical Society).

Dorr, Lewis, and co-workers found evidence through quenching experiments and flash spectroscopy for a triplex in the system trans-stilbene — amine — benzene — [105]. They quenched singlet excited trans-stilbene with various mono- and diamines and found a steric effect on the quenching constant The a, co-diamines (dabco, diaminoethane, -propane and -butane) quenched the stilbene fluorescence more efficiently than the monoamines, depending on the chain length between the amino groups. This was ascribed to the formation of cyclic radical cations, with a N-N three electron a-bond. In this case, an exciplex between diamine and stilbene is formed. 

Surprisingly, alkanes containing tertiary C—H bonds showed poor reactivity in these reactions.2943 b 29Sa d Thus, isobutane was less reactive than n-butane, and methylcyclohexane less reactive than cyclohexane (cf., lower reactivity of cumene to toluene). In the series of normal alkanes, n-butane reacted faster than n-pentane. n-Undecane was unreactive. These results are inconsistent with a normal free radical autoxidation. The authors used the analogy with arene oxidations to postulate that formation of radical cations by electron transfer from the alkane to Co(III) was a critical factor ... 

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. 

Gassman reported the photoaddition of nucleophiles to radical cations of highly strained aliphatic polycyclic molecules such as tricyclo[2.2.1.0 ]hexane and related compounds. The radical cation of bicyclo [1.1.0] butane is postulated as a key intermediate (Scheme 12) [45-46]. 

Figure 6. Schematic representation of the SOMOs for butane through hexane radical cations.

Catalysts active in the isomerization of n-butane have been synthesized by depositing sulfate ions on well-crystallized defective cubic structures based on ZrOz. This technique for introduction of sulfates does not result in any significant changes in the bulk properties of zirconium dioxide matrix. Active sulfated catalysts were prepared on the basis of cubic solid solutions of ZrOz with calcium oxide and on the basis of cubic anion-doped ZrOz. The dependence of the catalytic activity on the amount of calcium appeared to have a maximum corresponding to 10 mol.% Ca. Radical cations formed after adsorption of chlorobenzene on activated catalysts have been used as spin probes for detection of strong acceptor sites on the surface of the catalysts and estimation of their concentration. A good correlation has been observed between the presence of such sites on a catalyst surface and its activity in isomerization of n-butane. 

The ultraviolet spectra of saturated hydrocarbons are usually not very informative, and are dominated by Rydberg transitions.101 They correspond to the formation of a radical cation with the ejected electron being captured in a diffuse, atomlike orbital. Bicyclo[1.1.0]butane is the most extensively studied molecule of this group, and the Rydberg nature of the excited... 

In other examples, biphotonic ionization of 2,3-dimethyl-2,3-diphenyl-butane (bicumene) in TFE gives the bicumene radical cation which undergoes carbon-carbon fragmentation to yield the cumyl cation and cumyl radical [87]. Photoinduced electron transfer from 2,2-dialkyldioxolanes to tetra-cyanoanthracene gives radical cations which fragment to yield dialkoxy carbocations and alkyl radicals [88]. Benzyl acetals were subjected to two-pho-... 

The photodecomposition of 4-(6-methoxy-2-naphthyl)butan-2-one (nabume-tone) in water probably involves the formation of the nabumetone radical cation. This leads to the formation of 6-methoxy-2-naphthalene carboxalde-hyde. Further study has examined the photodegradation of this ketone in -butanol where it was shown that a first-order degradation took place. An excited singlet state is involved, and the author proposes that both concentration and hydrogen bonding are important in this solvent. 

Alkyl groups may also delocalize the unpaired electron and charge density in radical cations formed from strained alkanes. For example, radical cations of bicyclo[1.1.0]butane and l,3-dimethylbicyclo[1.1.0]butane have been detected in a Freon matrix following y-irradiation of the parent hydrocarbon (Figure 2.21). 

In equation 34 the primary intermediate is the 1,3-diradical, but alternatively a 1,3-zwitterion or Rydberg-like radical cation might be reached on 185-nm excitation 7-Irradiation of bicy do [1.1.0] butane was shown to generate a puckered 1,3-radical cation (Table 9 entry le) . This might be evidence for the above assumption of polar short-lived intermediates in the 185-nm photolysis of bicyclo[1.1.0]butanes. Therefore, 185-nm irradiation experiments were performed with the methylene-bridged derivatives of bicyclo[1.1.0]butane 66-68 (Table 9 entries 2c 3d,e 4c,d) in order to examine the involvement of polar intermediates. 

One-electron oxidation of alkanes leads to a-radical cations (equation 5.55). ° Such ionization removes an electron from an orbital associated with cr bonding among carbon atoms. The radical cation of butane, for example, shows elongation of the C2-C3 bond to a distance of about 2.0 A and a much lower difference in energies of the anti and gauche conformers than is the case with the parent hydrocarbon. Ionization of methane... 

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