Unstable Sulfur Species:Matrix Isolation Spectroscopy And Computational Studies

Unstable sulfur species are a kind of very important intermediates in systhentic chemistry,bioconversion,and the formation of atmospheric environmental pollutions.Due to their short lifetime and high reactivity,and there is little method for their efficient generation,the experimental investigation on sulfur species is always difficult in physical chemistry especially concerning their spectral data and elementary reactions such as photoisomerization and oxidation,although some theoretical researches on them are reported.This thesis focuses on three unstable sulfur species.Firstly,a reactive arylsulfinyl radical PhSO·,which is the significant intermediate in a variety of chemical transformation.Secondly,the simplest sulfinyl radical HSO·,which is the key intermediates in the atmospheric oxidation of H2S to sulfuric acid and interstellar sulfur chemistry.Thirdly,the interpseudohalogens bearing NSO,which are candidates for the high-energy density materials.The target surfur species have been generated in the gas phase through high-vacuum flash pyrolysis and laser photolysis of precursors.Then they are characterized in situ by using matrix isolation IR,UV-Vis spectroscopy and isotopic labeling.Furthermore,the spectral identification is supported by density functional theory and sophisticated ab initio theoretical method.Theoretical studies are also performed for predicting molecular structure,conformational isomerization,thermal stabilities and reaction pathway of intermediates.The main research contents include the following three parts:1.The parent radical PhSO·has been generated for the first time in the gas phase through high-vacuum flash pyrolysis of sulfoxide PhS(O)CF3 and sulfinyl chloride PhS(O)Cl at about 1000 K.Upon UV light irradiation(365 nm),PhSO· undergo[1,2]Ph-shift and isomerizes to novel oxathiyl radical PhOS.in cryogenic Ar matrices(2.8 K).Prolonged irradiation causes further isomerization of the PhOS· to 2-hydroxyphenylthiyl radical o-HOPhS·,the formation of which has been also observed in the 193 um laser photolysis of matrix-isolated 2-hydroxybenzenethiol.Concomitantly,ring-opening occurs during the UV photolysis of PhOS· and 2-hydroxybenzenethiol and forms an acyclic thioketoketene radical.Phenylsulfinyl radical reacts partially with molecular oxygen in the gas phase and yields phenyl radical Ph-and OSOO.Upon irradiation(365 n),the isomeric oxathiyl radical also combines O2 to PhOSOO·,which immediate dissociates to environmentally important phenoxy radical PhO· and SO2The isomerization,ring-opening,ring-expansion and decomposition of PhSO·have been discussed based on the computed potential energy profile and the comparison with the intensively explored photochemistry of phenylperoxy radical PhOO·.The identification of the intermediates with IR and UV-vis spectroscopy is supported by quantum chemical computations at the UCCSD(T)/aug-cc-pV(D+d)Z levels of theory.The mechanism for the isomerization of PhSO·is computed at the CCSD(T)/cc-pVTZ//B3LYP/def2-TZVPP level.2.The structure optimization,frequencies analysis,energies and transition state of HSO·and HOS·have been computed at the B3LYP/def2-TZVPP level.What's more,the feasibility of generating HSO·and HOS·through high-vacuum flash pyrolysis(HVFP)of-BuS(O)X(X=Cl and F)have been explored.In conclusion,for HSO·,the results of the cheap but efficient method B3LYP is nicely coincide with those of the sophisticated ab initio theoretical method and experimental data.The obvious distinctions in the theoretical IR spectrum may result in distinguishing HSO· from HOS· with matrix IR spectroscopy.Compared with previously observed RSO·?ROS.isomerization,the small isomezation energy between HSO and HOS·(2.2 kcal mol-1)may result in the reversible[1,2]H-shift of HSO·.The analysis of reaction pathway indicate that HSO· may be generated through high-vacuum flash pyrolysis(HVFP)of t-BuS(O)Cl,but cannot be generated through HVFP of t-BuS(O)F.In agreement with computations,the metastable thioether HOSX and sulfoxide HS(O)X have been generated through the HVFP of t-BuS(O)X(X=Cl and F)by elimination of 2-methypropene,but HSO· or HOS· are absent.The corresponding matrix IR spectra have been achieved.3.Comparing with the extensively studied high-energy species(N3-N3,N3-NCO,OCN-NCO),the interpseudohalogens bearing pseudohalogen NSO are barely known.By using quantum chemical calculations with the B3LYP,CBS-QB3,G4,and CCSD(T)methods,the molecular structures,conformation,vibrational data,and thermal stabilities of intriguing interpseudohalogens OSN-N3,OSN-NCO,and OSN-NSO have been studied.The computational results at different theoretical levels consistently suggest that both OSN-N3 and OSN-NSO prefer open-chain structures with diverse close-in-energy conformations due to a bent structure of the NSO moiety,whereas,the global minimum for OSN-NCO prefers a five-membered ring structure.The thermal stability follows the order of OSN-NSO>OSN-NCO>OSN-N3.The large N-N bond dissociation energies(?OSN·?NCO·,66.4 kcal mol-1;?2 NSO·,70.6 kcal mol-1 and higher fragmentation activation barrier(?N2+CO2+S,16.1 kcal mol-1;?cis-OSSO+ N2,25.8 kcal mol-1,CCSD(T)/CBS//B3LYP/aug-cc-pVTZ))respectively for OSN-NCO and OSN-NSO suggest their candidate observation at low temperatures.In contrast,the lower barriers for the concerted dissociation OSN-N3(?2 N2+SO,7.9 kcal mol-1)renders its experimental observation more difficult.Furthermore,base on the experimentally known Curtis-rearrangement of carbonyl azides and sulfinyl azides,the feasibility of access to the three interpseudohalegens through dissociation of the corresponding azide precursors OS(N3)2,OS(NCO)N3/OC(NSO)N3,and OS(NSO)N3 have been discussed with computational studies.