Re-Examination of the Effect of Aprotic Solvents upon the Fundamental Vibrational Peak of the Carbonyl Group in 1,1,3,3-Tetramethylurea

Abstract

The 1650 cm⁻¹ IR absorption band for the fundamental vibration of the C=O group in tetramethylurea (TMU) exhibits a substantial solvent-induced shift in polar and nonpolar aprotic solvents at 298 K. Earlier studies have rationalized the _max(C=O) shifts in terms of the empirical Gutmann acceptor numbers (ANs) for the solvents or the Kirkwood parameter in dielectric permittivity. With a larger set of test data, other reaction field models are now compared which incorporate alternative continuum functions as elements in the formulation of an SCRF-MO perturbation description for the aprotic solvent effect upon the _max(C=O) of TMU. The magnitude of the band shift appears to depend on both the solvent dipolarity and solvent polarizability, with the first being the dominant factor in the more reliable model.

Keywords

1,1,3,3-Tetramethylurea IR carbonyl group Solvent reaction field models Solvent-induced shift of the carbonyl band

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