Quantum yield diazirine

Photolytic transformation of diazirines to diazoalkanes was observed in some cases. The parent compound (44) on irradiation in the gas phase with light (A = 3200 A) yields diazomethane. The quantum yield is 0.2 (64JA292). 

The quantum yield of diazo compound formation from diazirines 43 and 44 was only 0.10-0.13, however, so that RIES was not considered an important product source during the diazirine photolysis. In the case of 44, for example, the substantial RIES contribution to chloroisobutene formation stems from excited 44, not from the excited state of its diazo isomer.55 The situation is analogous to the RIES formation of a-chlorostyrene during the photolysis of benzylchlorodiazirine.25... 

Photolysis of dialkyl- and alkyl-diazirines has been broadly investigated since the products formed gave evidence of shortlived intermediates possessing excess vibrational energy. As shown in Scheme 1 diazirines (3) were photoactivated to (235) by irradiation with a medium pressure mercury lamp with quantum yields smaller than one this means reversibly. Nitrogen extrusion yielded carbenes (236). These rearranged to the primary products, alkenes and... 

The quantum yield for the disappearance of the diazirine was found to be 2 0.5. The formation of the diazomethane corresponded to that of about one-tenth of the decomposition of the diazirine but leveled off during the photolysis. The authors su ested that this leveling off may have been due to secondary photolysis of the diazomethane by scattered radiation. These results set a lower limit for 0.2 for k /ki, i.e., at least 20% of the primary decomposition of the diazirine is an isomerization to diazomethane. Very surprisingly, no appreciable effect on the yield of diazomethane was found when nitrogen was added. 

The photolysis of diazirine °° at 3130 A yields ethylene and nitrogen methylene is probably formed in the primary process. The long wavelength absorption ( max = 3200 A) had been identified as the allowed (a, n ) transition and semi-empirical Huckel calculations indicate that the methylene produced must be (Ai) or (Bi). There is evidence that methylene produced from the photolysis of diazirine is more selective than methylene from diazomethane, owing to decreased excess translational energy. At low pressures 5-30 torr, diazomethane was identified as an intermediate by its absorption spectrum and the question arises, is methylene formed directly, or does it arise from decomposition of diazomethane The quantum yield of disappearance of diazirine is 2.0+0.5 and the quantum yield of diazomethane formation is about 0.2. The intermediate diazomethane is... 

Diazirines contain an N-N double boud constrained in a three-membered ring and have strong absorptions in both the infrared and ultraviolet/visible regions. The N=N stretching vibration of diazirines appears between 1560 and 1630 cm h In general, diazirines have an electronic absorption band between 310 and 350 nm (mi ), and a second absorption below 200 nm. Associated with the nJt transition is a weak fluorescence. " The fluorescence lifetime of adamantyldiazirine is on the order of 240 ps with a fluorescence quantum yield of about 0.0012 at ambient temperature. " (The lifetime increases with decreasing temperature.)... 

Bonneau and Liu performed time-resolved UV-VIS and standard spectroscopic experiments to determine the quantum yield for formation of carbenes and diazo compounds from several diazirines. In... 

---