| Autor: |
Smith CJ; Department of Chemistry, University of Minnesota , 207 Pleasant St., SE, Minneapolis, Minnesota 55455, United States., Huff AK; Department of Chemistry, University of Minnesota , 207 Pleasant St., SE, Minneapolis, Minnesota 55455, United States., Mackenzie RB; Department of Chemistry, University of Minnesota , 207 Pleasant St., SE, Minneapolis, Minnesota 55455, United States., Leopold KR; Department of Chemistry, University of Minnesota , 207 Pleasant St., SE, Minneapolis, Minnesota 55455, United States. |
| Abstrakt: |
The rotational spectrum of acrylic sulfuric anhydride (CH 2 ═CHCOOSO 2 OH, AcrSA) has been observed using pulsed-nozzle Fourier transform microwave spectroscopy. The species was produced from the reaction between acrylic acid and sulfur trioxide in a supersonic jet. Spectroscopic constants are reported for both the s-cis- and s-trans-AcrSA conformers of the parent and monodeuterated (OD) isotopologues. Geometries were optimized for both conformers using M06-2X/6-311++G(3df,3pd) methods. Single-point energy calculations at the M06-2X geometries were calculated using the CCSD(T)/complete basis set method with double and triple extrapolation [CBS(D-T)]. Further calculations indicate that the anhydride results from a π 2 + π 2 + σ 2 cycloaddition reaction within the acrylic acid-SO 3 complex. Because the C═O double bond of the acrylic acid migrates from one of the COOH oxygens to the other during the reaction, the s-cis form of acrylic acid leads to the s-trans form of the anhydride and vice versa. With zero-point energy corrections applied to the CCSD(T) energies, the s-cis and s-trans forms of CH 2 ═CHCOOSO 2 OH are 19.0 and 18.8 kcal/mol lower in energy than that of SO 3 + their corresponding CH 2 ═CHCOOH precursor conformation. The zero-point-corrected transition state energies for formation of the s-trans and s-cis anhydrides are 0.22 and 0.33 kcal/mol lower than those of the complexes of SO 3 with s-cis and s-trans acrylic acid, respectively, indicating that the reaction is essentially barrierless. This system adds to a growing body of examples demonstrating that carboxylic acids readily add to SO 3 in the gas phase to produce the corresponding carboxylic sulfuric anhydride. |
