Quantum chemical calculations have been performed to gauge the effect of pi-stacking and hydrogen bonding interactions on each other in X-ben//pyr...H-F (X = NO(2), CF(3), CN, F, Cl, CH(3) and OH) complexes. The results indicate the cooperativity of interactions in these complexes where face-to-face aromatic interactions and hydrogen bonding interactions coexist. The effects of substituents on the X-ben//pyr...H-F complexes have also been studied with the MP2 method using 6-31G** basis set. The total binding energy increases in both electron-donating and withdrawing substituents. Herein, computational results indicate an enhanced pi-stacking interaction for all substituted complexes related to an unsubstituted case. On the other hand, H...N hydrogen bond interaction is declined by strong electron withdrawing substituents (NO(2) and CN) only. The cooperativity of pi-stacking and H...N hydrogen bond interaction has also been studied by using the atoms in molecules (AIM), natural bond orbital (NBO) and molecular electrostatic potential (MEP) analyses. There are good relationships between the Hammett constants and energy data, geometrical parameters, and the results of population analysis in X-ben//pyr...H-F and X-ben//pyr complexes. The characteristics of interactions are directly related to the electrostatic interaction between the rings.

Experimental data of densities, viscosities, and refractive indices of {(benzyl alcohol + methanol), ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol} binary mixtures were measured at T = 298.15 K and ambient pressure (81 500 Pa) using an oscillating densimeter, Ubbelohde capillary viscometer, and digital Abbe refractometer, respectively. Values of excess molar volumes, V m E , of the binary mixtures in the liquid phase at T = 298.15 K have been derived from density measurements. The experimental data are used to calculate partial molar volumes, V i , excess partial molar volumes, V i E , excess partial molar volumes at infinite dilution, V i E,∞ , deviations in the viscosity, Δη, and deviations in the refractive index, Δn D , excess refractive index, n D E , and kinematic viscosity, ν. The calculated quantities V m E , Δη, Δn D , and n D E have been correlated with the Redlich−Kister equation. The excess partial molar volumes, V i E,∞ , and enthalpies, H i E,∞, at infinite dilution of the binary mixtures were computed by ab initio method at the M05-2X/6-311++G** level of theory using PCM theory in the liquid phase. The general agreement found between the computational and the experimental liquid-phase data gives confidence to calculate the excess partial molar volumes and enthalpies at infinite dilution.

The cooperative effects between T-shape stacking and hydrogen bond interactions in X-ben\pyrÁÁÁH-F complexes were investigated in this work. The results indicate that the electron-withdrawing/donating substituents decrease/increase the magnitude of the binding energies compared to the unsubstituted X-ben\pyrÁÁÁH-F (X = H) complex. The cooperative effects have been studied while using the atoms in molecules (AIM) and natural bond orbital (NBO) methods, allowing us to evaluate the interplay between T-shape stacking and hydrogen bond interactions. There are good relationships among binding energies, Hammett constants, geometrical parameters, and the results of AIM and NBO analysis in X-ben\pyrÁÁÁH-F complexes.

ABSTRACT:The effect of some substituents on intramolecular hydrogen bonding of 5-X-2-hydroxybenzaldehyde (5-X-2-HBA) has been studied by B3LYP and MP2 methods using 6-311ϩϩG** and AUG-cc-PVTZ basis sets. The relationship between hydrogen bond energy E HB and electron donation (or withdrawal) of substituents has been investigated. An approximately good linear relationship has been detected between Hammett coefficients and hydrogen bond formation energy (R 2 ϭ 0.98). Herein, population analysis has been performed by atoms in molecules (AIM) and natural bond orbital (NBO) methods. The results of AIM and NBO analyses are in a good agreement with calculated energy values. Furthermore, correlation between ring aromaticity and hydrogen bonding has been investigated by nucleus-independent chemical shift (NICS) at GIAO/B3LYP/6-311ϩϩG** level of theory.

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