Conformational and isomerizational studies of 3-N,N-dimethylhydrazino-2-methylsulfonyl propenenitrile using NMR and vibrational spectra, X-ray analysis and ab initio calculations

The IR, Raman and NMR spectra of 3-N,N-dimethylhydrazino-2-methylsulfonyl propenenitrile (DMHSP) [(H3C)2NNHCHC(CN) (SO2CH3)] as a solid and in different solvents were measured. The spectra and X-ray analysis revealed that DMHSP was prepared as a pure E-isomer and E-syn conformer with the syn orientation of N,N-dimethylhydrazino group towards the CC double bond in the solid state. Due to the low barrier practically free isomerization process occurred in solutions at room temperature. DMHSP exists in more polar solvents as pure E-isomer in conformational equilibrium between E-syn and E-anti but in a less polar solvent the presence of Z-isomer was observed as well. From the IR and NMR temperature dependence spectra in polar solvents the energy difference between E-anti and E-syn of ΔH = 2.3 ± 0.9 kJ/mol and ΔH = 3.2 ± 0.4 kJ/mol, respectively, was estimated with the syn one being more stable. ometries and relative energies of possible conformers of DMHSP were evaluated using ab initio MP2 and B3LYP density functional methods in 6-31G∗∗ basis set and compared with the X-ray data. The interpretation of NMR spectra was supported by ab initio MP2 calculations. The influence of solvent polarity on the conformational equilibrium is discussed with respect to the SCRF solvent effect calculations using PCM model. In addition, the observed IR and Raman bands were compared also with harmonic vibrational frequencies, calculated on the same levels of theory, and assigned on the base of potential energy distribution.