The structural organization of N-methyl-2-pyrrolidinone in binary mixtures probed by Raman spectroscopy: Experimental and quantum chemical results

The isotropic and anisotropic Raman spectra of N-methyl-2-pyrrolidinone (NMP) in the binary mixture at a variety of volume fractions have been measured. The noncoincidence effect (NCE) of NMP was determined separately in carbon tetrachloride (CCl4) solution and acetonitrile solution. The NCE of the (10)(C=O) stretching mode versus concentration in the NMP/acetonitrile mixtures exhibits a linear plot; however, the NCE behavior in the NMP/CCl4 mixtures shows an upward (convex) curvature. The dimer structure (short-range orientational order) of NMP may play a major role in exhibitions of different NCE behavior in the NMP/CAN and NMP/CCl4 mixtures; thus, the geometries of monomer and dimer of NMP were calculated at the B3LYP-D3/6-311G (d,p) level of theory. We proposed aggregated model to explain the NMP C=O vibration NCE phenomenon and its concentration effect and found it largely consistent with our experimental findings. Solvent-dependent experiment shows the value of NCE declined with increase the solvent dielectric constant under the same condition.