Gas-Phase Structure, Rotational Barrier, and Vibrational Properties of Methyl Methanethiosulfonate, CH3SO2SCH3: An Experimental and Computational Study

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• 作者：Marí ; a E. Tuttolomondo ; Amparo Navarro ; Tomá ; s Peñ ; a Ruiz ; Eduardo L. Varetti ; Stuart A. Hayes ; Derek A. Wann ; Heather E. Robertson ; David W. H. Rankin ; Aida Ben Altabef
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：October 4, 2007
• 年：2007
• 卷：111
• 期：39
• 页码：9952 - 9960
• 全文大小：302K
• 年卷期：v.111,no.39(October 4, 2007)
• ISSN：1520-5215

文摘

The molecular structure of methyl methanethiosulfonate, CH₃SO₂SCH₃, has been determined in the gas phasefrom electron-diffraction data supplemented by ab initio (HF, MP2) and density functional theory (DFT)calculations using 6-31G(d), 6-311++G(d,p), and 6-311G(3df,3pd) basis sets. Both experimental and theoreticaldata indicate that although both anti and gauche conformers are possible by rotating about the S-S bond, thepreferred conformation is gauche. The barrier to internal rotation in the CSSC skeleton has been calculatedusing the RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) methods as well as MP2 with a 6-31G(3df)basis set on sulfur and 6-31G(d) on C, H, and O. A 6-fold decomposition of the rotational barrier has beenperformed in terms of a Fourier-type expansion, enabling us to analyze the nature of the potential function,showing that the coefficients V₁ and V₂ are the dominant terms; V₁ is associated with nonbonding interactions,and V₂ is associated with hyperconjugative interactions. A natural bond orbital analysis showed that the lonepair * hyperconjugative interactions favor the gauche conformation. Furthermore, the infrared spectrafor the liquid and solid phases and the Raman spectrum for the liquid have been recorded, and the observedbands have been assigned to the vibrational normal modes. The experimental vibrational data, along withcalculated theoretical force constants, were used to define a scaled quantum mechanical force field for thetarget system that enabled us to estimate the measured frequencies with a final root-mean-square deviationof 6 cm^-1.