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Vibrational spectra and quantum chemical calculations of uracilyl–pyridinium mesomeric betaine
Author(s) -
Schmidt A.,
Lindner A. S.,
Casado J.,
Ramírez F. J.
Publication year - 2007
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1803
Subject(s) - chemistry , pyridinium , raman spectroscopy , molecule , protonation , conjugated system , computational chemistry , density functional theory , delocalized electron , crystallography , medicinal chemistry , organic chemistry , physics , ion , optics , polymer
Abstract Modified nucleobases (MNs) are promising molecules with potential application in non‐linear optic (NLO) and drug design against a wide number of diseases. In the present paper we report studies on a cross‐conjugated mesomeric betaine, which can act as a MN, formed by the covalent union of a 4‐dimethylamino pyridinium and a uracilyl groups. The molecule thus formed must be presented by a dipolar canonical formulae in which positive and negative charges are delocalized within separated moieties. Quantum chemistry density functional theory (DFT) calculations, at the B3PW91/6‐31G** level, and Fourier transform (FT) infrared and Raman spectra of this molecule and its N ‐deuterated derivative were performed. The calculated structural properties over the ground state optimized structure evidenced a strong separation between the two conjugated systems. Comparison with previous results obtained for the cationic species indicated that N ‐protonation clearly affects the degree of conjugation. Assignments of the FT‐IR and FT‐Raman spectra were supported by the DFT wavenumbers, intensities and normal modes, which also evidenced the separation of the two conjugated systems. Significant deviations were found for the stretching force constants of the inter‐ring and the uracilyl skeletal bonds when comparing this molecule with its N ‐protonated species. Copyright © 2007 John Wiley & Sons, Ltd.