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

Abstract 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 (CCl 4 ) solution and acetonitrile solution. The NCE of the ν 10 (C=O) stretching mode versus concentration in the NMP/acetonitrile mixtures exhibits a linear plot; however, the NCE behavior in the NMP/CCl 4 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/CCl 4 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.

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