Spectroscopic Detection And Reactivity Of Reactive Sulfur Species

Reactive sulfur species(RSS)play key roles in atmospheric chemistry,interstellar chemistry,biochemistry,organic synthesis,materials science.Obtaining the molecular structure,spectrum and reaction mechanism of RSS is of great significance for understanding the nature of chemical reaction.Due to their high reactivities and short-life,it ischallenging to study the structure and reactivity of RSS with conventional experimental methods and the previous studies of RSS mainly focused on theoretical exploration.In this dissertation,prototypes of RSS have been identified by matrix-isolation IR and UV/Vis spectroscopy,and reaction mechanism has been revealed by combining laser-induced photochemistry,isotope labelling,and quantum chemical calculations.The summary is as follows:1.Spectroscopic detection and formation mechanism of the radical pairs(RS·…·ON).The reversible interconversion between S-Nitro so thiols(RSNO)and RS·and NO· plays an important role in biological systems.Therefore,we used cryogenic matrix-isolation to capture the key intermediate for the RSNO decomposition reaction.The metastable radical pairs(RS·…·ON,R=Me,Et)were generated by the 365 nm irradiation of RSNO in cryogenic matrix-isolation(<10 K),and the reverse conversion was observed upon subsequent 830 nm irradiation.The radical pairs RS·…·ON were characterized by IR and UV/vis spectroscopy combined with 15N-isotopelabelling.Both experimental and theoretical results support the presence of O…S and H…N weak interactions in RS·…·ON,and the dissociation energy of MeS·…·ON amounts to 4.7 kcal mol-1.2.Spectroscopic detection and conformation transformation of the novel heterocumulenic radical OSNSO·.OSNSO· was generated in the gas phase through flash vacuum pyrolysis of CF3S(O)NSO at 400℃.The IR spectroscopic and theoretical analysis show that OSNSO· displays three conformations(syn-syn,syn-anti and anti-anti).The conformational interconversion occurs either through S=N bond rotation under selective visible light irradiation or through thermally initiated nitrogen-inversion in cryogenic matrices,and an exceptionally low activation barrier(1.18±0.07 kcal mol-1)for nitrogen-inversion(anti-anti to syn-syn)has been experimentally determined Natural bond orbital(NBO)analysis results show that the spin density of the unpaired electron in OSNSO· is almost equally delocalized on the oxygen and sulfur atoms.3.Spectroscopic detection and isomerization of sulfinyl radicals RSO·(R=CF3 and CH2CBr).Sulfinyl radicals are widely used in organic synthesis.To disclose their reactivity,the spetra and reaction mechanism of CF3SO· and CH2CBrSO· were studied by matrix-isolation IR spectroscopy and quantum chemical calculations.Upon 266nm laser irradiation,CF3SO· isomerizes to CF3OS· in cryogenic matrix-isolation.Whereas,visible-light irradiations result in syn(?)anti conformational interconversion in CH2CBrSO·.The spindensity in CF3SO· is mainly localized on the SO group,but in CH2CBrSO·,partial spin density is delocalized to terminal C atom.4.Spectroscopic detection and isomerization of the novel S2O2 and SO3 isomers.Sulfur oxides are important interstellar species,their spectra and reactivity are hot topic in interstellar chemistry.The fingerprint spectra and photochemistry of S2O2 and SO3 isomers were studied by combining matrix-isolation IR and UV/Vis spectroscopy with quantum chemical calculations.The syn OSSO,anti OSSO,cyclic OS(=O)S and syn SOSO,generated through the dimerization of gaseous SO and the reversible isomerization with its isomers were observed in matrix.The OSOO and cyclic OS(=O)O were generated from the O2-oxidation of SO in gas phase.Quantum chemical calculations show that the mechanism for the formation and interconversion of S2O2 and SO3 isomers are similar.