Cyanomethanesulfinyl Radical: Photoisomerization and Thermal Decomposition Reactions

The new cyanomethanesulfinyl radical •OSCH₂CN has been generated in the gas phase by high-vacuum flash pyrolysis (HVFP) of 2-(allylsulfinyl)acetonitrile at ca. 650 K and subsequently isolated in a solid Ar matrix at 10 K for characterization with matrix-isolation infrared (IR) spectroscopy. Upon photoexcitation at 430 nm, •OSCH₂CN undergoes an unexpected [1,3]-sigmatropic rearrangement to yield the novel keteniminyl-substituted sulfinyl radical CH₂CNSO• in the matrix, and the reverse isomerization occurs under further irradiation at 532 nm. When increasing the HVFP temperature to ca. 800 K, secondary gas phase fragmentation of •OSCH₂CN occurs via homolytic C-S bond cleavage, providing an efficient synthetic access to the cyanomethyl radical (•CH₂CN), which is an important intermediate in atmospheric and interstellar chemistry. Subsequent photoexication of •CH₂CN at 266 nm in the Ar matrix causes selective isomerization to •CH₂NC, enabling the observation of several new IR bands for the fundamental, overtone, and combination modes for •CH₂CN and •CH₂NC, and the assignment is supported by quantum chemical calculations using second-order vibrational perturbation theory at the CCSD(T)/aug-cc-pVTZ level of theory. Additionally, the gas phase oxidation of •CH₂CN by molecular oxygen in yielding the elusive peroxy radical •OOCH₂CN has also been observed.