Observation of Two Conformers of Acrylic Sulfuric Anhydride by Microwave Spectroscopy

C. J. Smith, Anna K. Huff, Rebecca B. Mackenzie, Kenneth R. Leopold

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The rotational spectrum of acrylic sulfuric anhydride (CH2=CHCOOSO2OH, 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 π2 + π2 + σ2 cycloaddition reaction within the acrylic acid-SO3 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 CH2=CHCOOSO2OH are 19.0 and 18.8 kcal/mol lower in energy than that of SO3 + their corresponding CH2=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 SO3 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 SO3 in the gas phase to produce the corresponding carboxylic sulfuric anhydride.

Original languageEnglish (US)
Pages (from-to)9074-9080
Number of pages7
JournalJournal of Physical Chemistry A
Issue number47
StatePublished - Nov 30 2017

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