| Small molecules of organophosphorus oxides,such as phosphinidene oxide(R-PO).dioxophosphorane(R-PO2)and monomeric metaphosphate(ROPO2),play important roles in synthetic chemistry,and they were proposed as key intermediates of organic phosphorus-containing flame retardants in the process of combustion and photochemical oxidation and degradation.The study on the spectra,structures and reactivity of these species has become one of the hot topics in organophosphorus chemistry in recent years,the study of conformational transformation and structural isomerism of related molecules has also become a hot topic in theoretical computational chemistry.In this paper,the diazide compounds CH3OP(O)(N3)2,CH3P(O)(N3)2 and methyl 2-butenylphosphonate as research objects,the low-temperature matrix isolation infrared spectroscopy was used to generate and characterize the unstable organic phosphorus oxide small,molecules CH3OPO,CH3PO2,and CH3OPO2with the aid of high-precision quantum chemical calculations.The corresponding reaction mechanism was discussed in depth.The specific research content is as follows1.The decomposition of CH3OP(O)(N3)2 was studied by low-temperature matrix isolation infrared spectroscopy.First,high-vacuum flash pyrolysis(HVFP)of the diazide CH3OP(O)(N3)2 at 1000 K,the cis and trans conformers of CH3OPO have been generated in the gas phase and subsequently isolated in cryogenic Ar and N2 matrices for IR spectroscopic characterization.Upon 266 nm laser irradiation of CH3OPO,cis→trans conformational conversion occurs,prolonged irradiation of CH3OPO leads to dominant formation of CH3PO2.The spectroscopic identification of these three species were supported by D-,13C-,and18O-isotope labeling and quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction(VCI),the band positions show good agreement with the calculated IR fundamentals.Upon 193 nm laser irradiation of azide precursor CH3OP(O)(N3)2 in N2 matrix,and its decomposed intermediate,the triplet CH3OP(O)(N3)N was observed.upon subsequent 365nm UV-light irradiation of nitrene,combined with 15N-labeling experiments and theoretical calculations,confirmed that secondary decomposition of nitrene occurred to produce N3· and CH3OP(O)N·With reference to the known potential energy surface of CH3ONO,based on the experimental results and theoretical calculations of CCSD(T)/aug-cc-pVTZ//B3LYP/6-311++G(3df,3pd),the decomposition and isomerization potential energy surfaces of CH3OPO were analyzed.2.The pyrolysis of methyl 2-butenylphosphonate and photooxidation of the CH3PO by O2 were studied by low-temperature matrix isolation infrared spectroscopy.The heavier phosphorus analogues of nitrate,monomeric methyl metaphosphate(CH3OPO2)was generated in the gas phase by high-vacuum flash pyrolysis(1000 K)of methyl 2-butenylphosphonate in solid N2-,Ar-,and Ne-matrices and the formation of CH3OPO2 was also observed in the photooxidation of CH3PO,generated by the HVFP of CH3P(O)(N3)2(→CH3PO+3N2),with molecular oxygen under the UV-light(365 nm)irradiation in N2 matrix.When the oxidation of CH3PO was performed with 18O2,an oxygen exchange phenomenon in CH3OPO2 was observed,the IR difference spectrumshows the formation of a mixture of three doubly 18O-labeled isotopomers.Unlike the oxidation of FPO(+O2→cyclic FP(=O)(O2)and FPO2),the reaction of CH3PO with O2 yields CH3OPO2,neither the cyclic isomer CH3P(=O)(O2)nor CH3PO2 was identified among the oxidation products.CH3P(=O)(O2)favors highly exothermic isomerization to CH3OPO2 by releasing 61.6 kcal/mol at the B3LYP/6-311++G(3df,3pd)level which is benefical to the isomerization of methyl migration.However,the fluorine-shift in cyclic FP(=O)(O2)to form FOPO2 is unfavourable since the latter is 33.3 kcal/mol higher in energy,which is not conducive to fluorine atom migration.Natural population analysis(NPA)show that CH3OPO2 is a highly electrophilic intermediate in phosphorylation reactions. |
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