Add time:08/28/2019         Source:sciencedirect.com

Density functional theory (DFT) calculations at the B3LYP/6-311 ++G** level of theory were realized to analyze the effect of various solvents on the hydrogen bond (HB) strength of 5-aminomethylene-pyrimidine-2, 4, 6 trion and its 22 derivatives in R position. The influence of the solvent was considered using the Tomasi's Polarized Continuum Model (PCM). The geometry optimization, π electron delocalization, vibrational frequencies and several well-established indices of aromaticity have been evaluated at the same level of theory. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent density functional theory method. The results show that the HB strength of 5-aminomethylene-pyrimidine-2, 4, 6 trion and its derivatives in non-polar solvent is higher than polar solutions. Its HB strength in polar solvent with respect to water as natural solvent is close to each other. A set of mostly common substituents having different properties in resonance effect according to values of substituent constants were chosen to simulate the influence of substitution in R position of title molecule on the quasi-delocalization and H-bonding. The substituent effect is also analyzed and it is found that the strongest/weakest hydrogen bonds exist for CN/CHO substitutions. The intramolecular hydrogen bonding (IMHB) interaction has been explored by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the Bond Critical Point (BCP) using Atoms-in-Molecule (AIM) theory. Natural bond orbital analysis (NBO) was performed for better understanding of the nature of intramolecular interactions. The aromaticity is measured using several well-established indices of aromaticity such as NICS, HOMA, PDI, FLU, and FLUπ. The calculated chemical shifts of the chelated proton for all molecules, using GIAO method, are well correlated with the calculated geometrical parameters results.

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