Structure and conformation of thioanisole: Gas electron diffraction and contradicting quantum chemical calculations

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• 作者：Igor F. Shishkov ; Lyudmila V. Khristenko ; Nikolai M. Karasev ; Lev V. Vilkov ; Heinz Oberhammer
• 关键词：Thioanisole ; Molecular structure ; Conformational properties ; Gas-phase electron diffraction ; Quantum chemical calculations
• 刊名：Journal of Molecular Structure
• 出版年：2008
• 出版时间：17 February 2008
• 年：2008
• 卷：873
• 期：1-3
• 页码：137-141
• 全文大小：187 K

文摘

The geometric structure and conformational properties of thioanisole, C₆H₅SCH₃, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations. The GED intensities are fitted very well with a single conformer with planar orientation of the S–CH₃ bond (φ(C–S) = 0°). The experimental potential function for internal rotation around the C(sp²)–S bond derived with a dynamic model possesses a single minimum for planar conformation, but a second shallow minimum for perpendicular orientation cannot be excluded. Calculated potential functions depend strongly on the computational method. The MP2 approximation with small basis sets (6-31G(d)) predict a single minimum for perpendicular orientation, (φ(C–S) = 90°), with intermediate basis sets (6-311G(d,p)) an additional shallow minimum for planar orientation and with large basis sets (cc-pVTZ) the global minimum for planar orientation and an additional shallow minimum at φ(C–S) = 90°. The B3LYP/cc-pVTZ calculations result in a single minimum for planar orientation, in agreement with the GED experiment. The experimental and calculated barrier to internal rotation is about 1 kcal/mol. The following geometric parameters (r_a and mg src=""http://www.sciencedirect.com/scidirimg/entities/2220.gif"" alt=""angle"" border=0>_h1 with 3σ uncertainties) were derived: r(C–C)_av = 1.395(3) Å, r(C(sp²)–S) = 1.775(4) Å, r(S–CH₃) = 1.813(4) Å, mg src=""http://www.sciencedirect.com/scidirimg/entities/2220.gif"" alt=""angle"" border=0>CSC = 104.5(5), mg src=""http://www.sciencedirect.com/scidirimg/entities/2220.gif"" alt=""angle"" border=0>C2C1C6 = 119.3(3), mg src=""http://www.sciencedirect.com/scidirimg/entities/2220.gif"" alt=""angle"" border=0>C1C2C3 = 120.2(4)°.