Energetic and Structural Study of Diphenylpyridine Isomers

Abstract

The energetic and structural study of three diphenylpyridine isomers is presented in detail. The three isomers, 2,6-, 2,5-, and 3,5-diphenylpyridines, were synthesized via Suzuki-Miyaura methodology based on palladium catalysis, and the crystal structures of the isomers were obtained by X-ray diffraction. The relative energetic stabilities in the condensed and gaseous phases as well as volatilities and structures of the three studied isomers were evaluated, regarding the position of the phenyl groups relative to the nitrogen atom of the pyridine ring. The temperature, standard molar enthalpies, and entropies of fusion were measured and derived by differential scanning calorimetry. The vapor pressures of the considered isomers were determined by a static apparatus based on a MKS capacitance diaphragm manometer. The standard molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived, and the phase diagram near the triple point coordinates were determined for all isomers. The standard (p(o) = 0.1 MPa) molar enthalpies of combustion of all crystalline isomers were determined, at T = 298.15 K, by static bomb combustion calorimetry. The standard molar enthalpies of formation, in the crystalline and gaseous phases, at T = 298.15 K, were derived. The experimental results for the energetics in the gaseous phase of the three compounds were compared and assessed with the values obtained by ab initio calculations at different levels of theory (DFT and MP2) showing that, at this level of theory, the computational methods underestimate the energetic stability, in the gaseous phase, for these molecules. In order to understand the aromaticity in the central ring of each isomer, calculations of NICS (B3LYP/6-311G++(d,p) level of theory) values on the pyridine ring were also performed.

Identification and characterization of phenylacetonitrile as a nitrogenous disinfection byproduct derived from chlorination of phenylalanine in drinking water

“…Panzella et al (2005) reported that the reaction of either 3-nitrotyrosine or phenylalanine with hypochlorous acid led to the formation of 3,5-diphenylpyridine arising from a Chichibabin-like pyridine synthesis via N-chloroimine intermediates. The isomers, 2,6-DPhPy and 3,5-DPhPy could be synthesized via the SuzukiMiyaura method based on palladium catalysis (Rocha et al, 2009), with the production of halogenated organic compounds. In our study, phenylacetaldehyde and halogenated organic compounds like chloromethyl benzene, and chlorophenylacetaldimine were identified by GC-MS or HPLC-MS, therefore, the presence of the isomer of 2,6-diphenylpyridine was assumed to be related to the above products.…”

N‐Confused Pyritriphyrin: A New Class of Triphyrin and Its Calixphyrin Analogue

“…1.1.1 ) 7 . The crystal analysis reveals the following; (i) both the pyrrole units are amine type (N1‐H1′ and N3‐H3′), such exclusive presence of dipyrromethane unit in macrocylic core is hitherto unknown in the calixphyrin chemistry; (ii) one of the pyrrole unit (N1) is highly tilted by 68.84(5)° as compared to other pyrrole (N3) 30.78(5)° and pyridine units ( Py ) by 55.91(4)° and these units were deviated from the mean macrocyclic plane containing 16 inner core atoms; (iii) overall the macrocycle exhibits partial ruffled conformation to mitigate the steric repulsion caused by the contracted core and (iv) as compared to 3,5‐diphenylpyridyl unit, [17] the inverted pyridine ring is almost perpendicular to the fused‐phenyl units with the dihedral angle of 85.09(5)° ( o1 ) and 66.67(6)° ( o2 ), respectively. Furthermore, the carbon–carbon bond lengths of pyridine( Py ) unit in 7 are between 1.396(2) Å and 1.336(2) Å, pyrrole rings (N1 & N3) are from 1.425(2) Å to 1.357(2) Å and phenyl rings ( o1 & o2 ) are between 1.401(2) Å and 1.370(2) Å (Figure S23) confirms that each heterocyclic rings maintain its individual aromatic character.…”