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

Abstract

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 2.94/2.91kcal/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.