Investigation on the dipole–dipole interactions between tetramethylurea and acetonitrile by two-dimensional asynchronous spectroscopy

• DAOSD approach is used to probe interaction between tetramethylurea and acetonitrile.
• Under interaction, νCO red-shifts and the absorptivities of νCO, νCN decrease.
• Under interaction, variation percentage of the of ε of νCN, δCH3 + νCC are the same.

Double Asynchronous Orthogonal Sample Design scheme (DAOSD) proposed in our previous work is used to probe dipole–dipole interaction between CO and CN groups in tetramethylurea/CD3CN systems. The results indicate that the carbonyl band of tetramethylurea undergoes a red shift and the absorptivity of the carbonyl band of tetramethylurea and νCN of CD3CN decreases under intermolecular interaction. Then the interaction between tetramethylurea and CH3CN was also detected. Besides CO and CN groups, the spectral behavior of a combination band (δCH3 + νCC) of CH3CN was also investigated. The spectral behavior is somewhat similar to the TMU/CD3CN system. However, a noticeable feature is observed on the relationship between νCN band at 2254 cm−1 and the δCH3 + νCC band at 2292 cm−1 of CH3CN: no cross peak was observed at (2254, 2292) in the 2D asynchronous spectrum. Mathematical analysis indicates that absence of the cross peak can occur only when the variation of the absorptivity of νCN and that of δCH3 + νCC band are in the same proportion. Thus, the DAOSD approach reveals an unexpected relationship on the spectral behavior of the νCN and δCH3 + νCC band under intermolecular interaction.