Abstract
Theoretical calculations were carried out using the DFT/B3LYP/6-31+G(d) methodology in an attempt to predict the preferred interaction site of a polyfunctional heterocyclic base 3-methyl-4- pyrimidone molecule with a series of proton donors of different acidic strength, i.e. water, methanol, phenol, 1-naphtol, 2,4,5 trichlorophenol, pentachlorophenol, picric acid and hydrogen chlordide. Computed H-bond interaction energies (ΔEc), internuclear and intermolecular distances r(O…H) and r(O…O), infrared frequency shifts Δv(C=O) and (Δv(OH) are proved to be reliable parameters for predicting the preferred interaction site of 3-methyl-4-pyrimidone. These computational data suggest that the O-H…O=C complex is preferred with water, methanol, phenol, 1-naphtol, 2,4,5 trichlorophenol and pentachlorophenol. However, for H-bonding with stronger acids such as picric acid or hydrochloric acid, the computational data suggest that the H-bonding occurs at the N1 ring atom of 3-methyl-4-pyrimidone. In the O-H…O=C com- plex, where the H-bond at the carbonyl O-atom can be oriented “anti” (Ha) and “syn” (Hb) with respect to the N3 atom, the same computational data suggest a higher stability of the “anti-O” compared to the “syn-O” orientation.
Highlights
Theoretical [Density Functional Theory (DFT)-B3LYP/6-31+G(d)] and experimental investigations are suitable to discriminate between O-H...N and O-H...O=C complexes of 3-methyl-4-pyrimidone (3M4P) and proton donors [1,2,3,4]
Theoretical [DFT-B3LYP/6-31+G(d)] and experimental investigations are suitable to discriminate between O-H...N and O-H...O=C complexes of 3-methyl-4-pyrimidone
Experimental frequency shifts of (C=O), (C=O), (C=O) and (N1=C) modes of 3-methyl-4-pyrimidone, which are sensitive to Hbonding, the values of the H-bond interaction energy (ΔEc) and the internuclear and intermolecular distances computed at the DFT(B3LYP)/6-31+G(d) level of theory have been shown that H-bonds between weak acids such as methanol are formed preferentially at the carbonyl group, whereas for stronger acids such as hydrochloric acid the complexation occurs on the N1 atom of the ring
Summary
Theoretical [DFT-B3LYP/6-31+G(d)] and experimental (matrix-isolation Infrared, denoted IR, spectroscopy) investigations are suitable to discriminate between O-H...N and O-H...O=C complexes of 3-methyl-4-pyrimidone (3M4P) and proton donors [1,2,3,4]. Experimental frequency shifts of (C=O), (C=O), (C=O) and (N1=C) modes of 3-methyl-4-pyrimidone, which are sensitive to Hbonding, the values of the H-bond interaction energy (ΔEc) and the internuclear and intermolecular distances computed at the DFT(B3LYP)/6-31+G(d) level of theory have been shown that H-bonds between weak acids such as methanol are formed preferentially at the carbonyl group, whereas for stronger acids such as hydrochloric acid the complexation occurs on the N1 atom of the ring In spite of these exciting results, no other, detailed studies on reliable theoretical parameters on the preferred interaction site of the polyfunctional heterocyclic base 3M4P are available in the literature. In both cases the prediction of the preferred interaction site due to only the acidity of the proton donor can be modified
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