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

Double Asynchronous Orthogonal Sample Design scheme (DAOSD) proposed in our previous work is used to probe dipole-dipole interaction between C:=O and C equivalent to N 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 V-C equivalent to N of CD3CN decreases under intermolecular interaction. Then the interaction between tetramethylurea and CH3CN was also detected. Besides C=O and C equivalent to N groups, the spectral behavior of a combination band (delta(CH3) + VC-C) 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 V-C equivalent to N band at 2254 cm(-1) and the delta(CH3) + VC -C 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 V-C equivalent to N., and that of delta(CH3) + VC-C band are in the same proportion. Thus, the DAOSD approach reveals an unexpected relationship on the spectral behavior of the vN and delta(CH3) + VC-C band under intermolecular interaction. (C) 2014 Elsevier B.V. All rights reserved.