A theoretical study on three conformational structures of 2,6‐distyrylpyridine

Abstract

ABSTRACT:Ab initio methods at the levels HF/cc-pVDZ, HF/6-31G(d,p), MP2/ccpVDZ, and MP2/6-31G(d,p), as well as methods based on density functional theory (DFT) employing the hybrid functional B3LYP with the basis sets cc-pVDZ and 6-31G(d,p), have been applied to study the conformers of 2,6-distyrylpyridine. Bond distances, bond angles, and dihedral angles have been calculated at the B3LYP level.The calculated values were in good agreement with those measured by X-ray diffraction analysis of 2,6-distyrylpyridine. The values calculated using the Hartree-Fock method and second-order perturbation theory (MP2) were inconsistent. The optimized lowestenergy geometries were calculated from the reported X-ray structural data by the B3LYP/cc-pVDZ method. Three conformations, A, B, and C, were proposed for 2,6-distyrylpyridine. Calculations at the three levels of theory indicated that conformation A was the most stable structure, with conformations C and B being higher in energy by 1.10 and 2.57 kcal/mol, respectively, using the same method and basis function. The same trend in the relative energies of the three possible conformations was observed at the two levels of theory and with the different basis sets employed. The reported X-ray data were utilized to optimize total molecular energy of conformation A at the different calculation levels. The bond lengths, bond angles, and dihedral angles were then obtained from the optimized geometries by ab initio methods and by applying DFT using the two basis functions cc-pVDZ and 6-31G (d,p). The values were analyzed and compared. The calculated total energies, the relative energies of the molecular orbitals, the gap between them, and the dipole moment for each conformational structure proposed for 2,6-distyrylpyridine are also reported.

Theoretical and Experimental Spectroscopic Analysis of Cyano-Substituted Styrylpyridine Compounds

“…Model compounds in trans conformation or with the group CN attached to double bond or in the aromatic ring [17–21] have been studied to comprehend the effect in the optics and electronic properties. One of our studies on styrylpyridines derivatives was on 2,6-distyrylpyridine [22,23]. The characterization results by X-ray showed that although the molecule is plane, it did not exhibit a total delocalization of its electrons through the whole molecule.…”

“…Also, the results showed that depending on the trans spatial arrangement of double bonds, there were three possible conformations. The theoretical calculations reported showed the conformational and structural analyses of 2,6-distyrylpyridine conformations using ab initio methods, as well as methods based on density functional theory, DFT [23]. The results determined that the conformation depends on the double bond orientation by the trans proton steric effect with protons in the ortho position of the phenyl or with pyridine groups.…”

“…Several styrylpyridine-like compounds—2-styrylpyridine, its derivatives and intermediates [24–27], 4-styrylpyridine and its intermediates [27–29], 2,6-distyrylpyridine [23,27], pyridinevinylenes [30] and phenylpyridylacrylonitriles [19]—have been synthesized under green chemistry conditions. Some have been characterized by X-ray diffraction [22,24–29], IR [19,22,25–30], 1 H-NMR [19,24–30], UV-Vis [19,28], mass spectroscopy [19,27] and complementary theoretical studies [23,31].…”

“…Some have been characterized by X-ray diffraction [22,24–29], IR [19,22,25–30], 1 H-NMR [19,24–30], UV-Vis [19,28], mass spectroscopy [19,27] and complementary theoretical studies [23,31]. Theoretical calculations on 2,6-distyrylpyridine [23,31], 4-styrylpyridine [32,33] and 2-styrylpyridine and derivatives [34] have been carried out using ab initio and Density Functional Theory (DFT) approximations.…”

“…In this work, the B3LYP calculations fit the experimental data better than HF-derived values in evaluating vibrational frequencies and geometrical parameters [31]. Melendez et al [23], carried out a study of three conformational structures of 2,6-distyrylpyridine using HF, second-order Moller-Plesset (MP2) and B3LYP methods with 6-31G(d,p) and cc-pVDZ basis sets. The authors indicated that B3LYP and MP2 methods with the cc-pVDZ basis set would be good choices for structural, stability and reactivity analyses for these kinds of compounds [23].…”