Photochemical Ring-Opening Reaction in 2(1H)-Pyrimidinones:  A Matrix Isolation Study

Abstract

Photoreactions induced by UV-B (290-320 nm) irradiation were studied for 1-methyl-2(1H)-pyrimidinone and 1-methylcytosine monomers isolated in low-temperature inert gas matrixes. A Norrish type I R-cleavage reaction leading to open-ring conjugated isocyanate was observed for 1-methyl-2(1H)-pyrimidinone. The structure of the photoproduct was identified by comparison of its experimental IR spectrum with the spectrum theoretically calculated at the DFT(B3LYP)/6-31++G(d,p) level. The main indication of isocyanate as a photoproduced species was the appearance in the infrared spectrum recorded after UV irradiation of a very strong band at a characteristic frequency of 2263 cm -1 . Observation of a new band at nearly the same frequency in the spectrum of UV-irradiated monomeric 1-methylcytosine may suggest that also in the case of this compound a conjugated isocyanate is photoproduced.

Five isomers of monomeric cytosine and their interconversions induced by tunable UV laser light

“…The amount of this product photogenerated from cytosine must be really tiny, because the observed intensity of the spectral signature at ca. 2266 cm À1 was low and absolute intensities of IR bands due to ''antisymmetric'' stretching vibrations of the -NQCQO isocyanate groups are very high, 18,19 usually higher than 1000 km mol À1 .…”

UV-induced unimolecular photochemistry of 2(5H)-furanone and 2(5H)-thiophenone isolated in low temperature inert matrices

“…2140-2125 cm À1 [19][20][21][22]31,32]) of ketene group (C C O) appears in the spectrum of the irradiated sample, thus providing evidence for the generation of the thioaldehyde-ketene (T) resulting from the ring-opening photoreaction.…”

The Excited‐State Decay of 1‐Methyl‐2(1H)‐pyrimidinone is an Activated Process

“…Lapinski et al [22] performed matrix isolation experiments on the photochemistry of 1MP. Its illumination in an argon matrix resulted in the formation of isocyanates via a ring-opening reaction, in contrast to what is observed when illuminating (6-4) lesions in solution.…”