Photoelimination from Hydrocarbons

The vacuum UV photochemistry of the allyl radical, generated by flash pyrolysis, has been investigated in a study using synchrotron radiation, in which mass spectra recorded over a wide energy range showed the appearance of the C3H3+ fragment from dissociative photoionization above 10 eV.  

The benzyl radical and several deuteriated isotopomers have been generated in methylcyclohexane at 4.2 K by UV-photolysis of toluene or deuteriated toluene, and a detailed vibrational analysis of the fluorescence spectra carried out. The photodissociation dynamics of azulene at 193 nm have been studied in a molecular beam using multimass ion-imaging techniques. Most of the excited molecules produced at this wavelength relax rapidly to the electronic ground state through internal conversion, then isomerize to naphthalene, and eventually dissociate by H-atom elimination. 

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In contrast to aromatic hydrocarbons, heavy-atom substitution onto carbonyl and heterocyclic molecules appears to have little effect on radiative and nonradiative intercombinational transitions. Wagner(138) has shown that as determined by the type II photoelimination, aliphatic ketones (n -> it excited states) are not sensitive to external heavy-atom perturbation. As seen previously in our discussion of type II photoelimination, aliphatic ketones undergo this cleavage from both the excited singlet and triplet states (in... 

A novel photoelimination of nitrogen from the 1,1-diazene (148) has been reported giving the hydrocarbons (149)—(152). A competing process leading to the tetrazene (153) has also been observed, and both types of reaction product appear to be singlet- and triplet-derived. 

Photoelimination of nitrogen from diazo-compounds is a simple and versatile process for the generation of carbenes. The diazoadamantane (65) is a surprisingly stable compound which on irradiation yields the hydrocarbon (66), the azine (67), and the alcohol (68) via the carbene. The origin of the oxygen atom... 

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