Mechanism, photochemical actinometer

The author showed, that only UV light was active and that a polar solvent was required and described the reaction as a benzylic heterolysis. This and related photochemical reactions with the leuco derivatives of crystal violet and malachite green were later studied in detail in their mechanism [3-9] and were among the first compounds proposed as chemical actinometers [10-12], although in the event these were found to be less suited than other derivatives, since the high sensitivity was counterbalanced by the high absorption of the photoproducts in the UV. 

Measurements of photochemical quantum yields have proved to provide critical information for the determination of the mechanism of the photoreaction. In solution and in the gas phase, such quantitative measurements of photoreactions are readily carried out using the chemical actinometers described in the previous sections. The quantum yields of solid-state photoreactions are more difficult to obtain for two... 

Since the absolute intensity of an irradiation source is difficult to determine by physical methods, photochemists prefer the use of a simple photochemical reaction for the measurement of intensity. Any photoreaction for which the mechanism is known to be simple can be used as a chemical actinometer. It requires that the photochemical quantum yield is determined and independent of intensity or other effects. 

Where is the quantum yield. The quantum yield of photochemical reactions is important because it sheds light on the mechanisms of reactions. The number of molecules involved in a particular photoreaction can be established by an analytical kinetic process and the number of quanta absorbed can be measured with the aid of an actinometer. The quantum yield can also be expressed in general kinetic terms ... 

Nitrobenzaldehydes have not been reported as products of the atmospheric oxidation of toluene, but these compounds could conceivable be formed through the oxidation of toluene in an NOjc-rich atmosphere. o-Nitrobenzaldehyde has been used successfully as an actinometer in photochemical studies (Pitts et al., 1964), and in this sense a brief discussion of its photochemistry is given here. The photochemistry of o-nitrobenzaldehyde has been studied in acetone and ligroin solutions (Leighton and Lucy, 1934a, b), in the pure solid (Bowen et al., 1924), and in KBr matrices (Pitts et al., 1964). Photolysis results in the ultimate isomerization to o-nitrosobenzoic acid, stmcture C (reaction mechanism IX-L-5). 

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