| Autor: |
Huff AK; Department of Chemistry, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States., Mackenzie RB; Department of Chemistry, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States., Smith CJ; Department of Chemistry, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States., Leopold KR; Department of Chemistry, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States. |
| Abstrakt: |
Acetic sulfuric anhydride, CH 3 COOSO 2 OH, was produced by the reaction of SO 3 and CH 3 COOH in a supersonic jet. Four isotopologues were observed by microwave spectroscopy. Spectra of both A and E internal rotor states were observed and analyzed, yielding a value of 241.093(30) cm -1 for the methyl group internal rotation barrier of the parent species. Similar values were obtained for the other isotopologues studied. M06-2X/6-311++G(3df,3pd) calculations indicate that the formation of the anhydride proceeds via a π 2 + π 2 + σ 2 cycloaddition reaction within the CH 3 COOH-SO 3 complex. The equilibrium orientation of the methyl group relative to the O═C-C plane is different in the anhydride and in the CH 3 COOH-SO 3 complex, indicating that the -CH 3 internal rotation accompanies the cycloaddition reaction. The energies of key points on the potential energy surface were calculated using CCSD(T)/complete basis set with double and triple extrapolation [CBS/(D-T)], and the transformation from the CH 3 COOH-SO 3 complex to CH 3 COOSO 2 OH is shown to be nearly barrierless regardless of the orientation of the methyl group. This study provides the second experimental observation of the reaction between a carboxylic acid and SO 3 to form a carboxylic sulfuric anhydride in the gas phase. Possible connections to atmospheric aerosol formation are discussed. |
