The difference between gas-phase and crystal structures of ortho-nitromethylbenzenesulfonate. Conformation variety study of free molecules by electron diffraction and quantum chemistry

• Ortho-nitromethylbenzenesulfonate molecules possess six conformers.
• The structure of each conformer is determined by ortho- and cog wheel effects and by anomeric effects inside SO2OCH3 group.
• According to gas-phase electron diffraction data, the conformer of lowest calculated energy predominates in vapor at 380 K.
• In the crystal the molecular structure is similar to a high energy conformer.

The conformational composition of the vapor (T = 380(5) K) and the conformer structures of ortho-nitromethylbenzenesulfonate (NO2С6H4SO2OCH3, 2-NMBS) molecule have been studied by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) method complemented by the results of quantum chemical calculations. According to calculations (MP2/B3LYP, cc-pVTZ), the molecule 2-NMBS possesses six conformers with relative energies ΔЕ = 0/0; 0.54/1.08; 0.69/0.89; 0.81/1.77; 1.68/2.22 and 2.94/2.91 kcal/mol. The geometrical parameters (Å and degrees) of the prevailing conformer were determined by GED (uncertainties are in parentheses): rh1(CC)av = 1.400(5), rh1(CS) = 1.781(6), rh1(SO) = 1.588(5), rh1(SO)av = 1.427(10), rh1(CN) = 1.469(15), rh1(CO) = 1.487(16), rh1(NO)av = 1.236(10), φ(CCSO) = −96(7), φ(CSOC) = 139(9). It is shown that the relative orientation of SO2OCH3 and NO2 groups in the structure of each of the six conformers is determined by ortho- and cog wheel effects and by anomeric effects inside the SO2OCH3 group. The reliability of the structure estimation of free 2-NMBS molecules on the base of X-ray data is discussed.

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