Samira Dalbouha

In the title molecule, C₁₄H₁₁NO₃, the dihydroquinoline core deviates slightly from planarity, indicated by the dihedral angle of 1.07 (3)° between the two six-membered rings. In the crystal, layers of molecules almost parallel to the bc plane are formed by C—H...O hydrogen bonds. These are joined by π–π stacking interactions. A Hirshfeld surface analysis revealed that the most important contributions to the crystal packing are from H...H (36.0%), H...C/C...H (28.9%) and H...O/O...H (23.5%) interactions. The evaluation of the electrostatic, dispersion and total energy frameworks indicates that the stabilization is dominated by the dispersion energy contribution. Moreover, the molecular structure optimized by density functional theory (DFT) at the B3LYP/6-311G(d,p) level is compared with the experimentally determined molecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

The asymmetric unit of the title compound, C₁₀H₁₂N₄O₂S, contains two molecules differing slightly in the orientations of the methyl groups. In the crystal, a sandwich-type structure extending parallel to the ab plane is formed by weak C—H...O and C—H...N hydrogen bonds together with slipped π-stacking interactions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H...H (43.5%), H...O/O...H (17.9%) and H...N/N...H (17.4%) interactions. The molecular structure optimized by density functional theory (DFT) at the B3LYP/ 6–311 G(d,p) level is compared with the experimentally determined structure in the solid state. Further calculations include the HOMO–LUMO energies and molecular electrostatic potential (MEP) surfaces.

In the title molecule, C₇H₆N₄O₃, the bicyclic ring system is planar with the carboxymethyl group inclined by 81.05 (5)° to this plane. In the crystal, corrugated layers parallel to (010) are generated by N—H...O, O—H...N and C—H...O hydrogen-bonding interactions. The layers are associated through C—H...π(ring) interactions. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H...O/O...H (34.8%), H...N/N...H (19.3%) and H...H (18.1%) interactions. The volume of the crystal voids and the percentage of free space were calculated to be 176.30 ų and 10.94%, showing that there is no large cavity in the crystal packing. Computational methods revealed O—H...N, N—H...O and C—H...O hydrogen-bonding energies of 76.3, 55.2, 32.8 and 19.1 kJ mol⁻¹, respectively. Evaluations of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via dispersion energy contributions. Moreover, the optimized molecular structure, using density functional theory (DFT) at the B3LYP/6–311G(d,p) level, was compared with the experimentally determined one. The HOMO–LUMO energy gap was determined and the molecular electrostatic potential (MEP) surface was calculated at the B3LYP/6–31G level to predict sites for electrophilic and nucleophilic attacks.

In the title compound, C₁₂H₁₀ClNO₃, the dihydroquinoline moiety is not planar with a dihedral angle between the two ring planes of 1.61 (6)°. An intramolecular C—H...O hydrogen bond helps to establish the rotational orientation of the carboxyl group. In the crystal, sheets of molecules parallel to (10\overline{1}) are generated by C—H...O and C—H...Cl hydrogen bonds, and are stacked through slipped π-stacking interactions between inversion-related dihydroquinoline units. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (34.2%), H...O/O...H (19.9%), H...Cl/Cl...H (12.8%), H...C/C...H (10.3%) and C...C (9.7%) interactions. Computational chemistry indicates that in the crystal, the C—H...Cl hydrogen-bond energy is −37.4 kJ mol⁻¹, while the C—H...O hydrogen-bond energies are −45.4 and −29.2 kJ mol⁻¹. An evaluation of the electrostatic, dispersion and total energy frameworks revealed that the stabilization is dominated via the dispersion energy contribution. Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state, and the HOMO—LUMO behaviour was elucidated to determine the energy gap.

Torsional and rotational spectroscopic properties of pyruvic acid are determined using highly correlated ab initio methods and combining two different theoretical approaches: Second order perturbation theory and a variational procedure in three-dimensions. Four equilibrium geometries of pyruvic acid, Tc, Tt, Ct, and CC, outcome from a search with CCSD(T)-F12. All of them can be classified in the C_s point group. The variational calculations are performed considering the three internal rotation modes responsible for the non-rigidity as independent coordinates. More than 50 torsional energy levels (including torsional subcomponents) are localized in the 406–986 cm⁻¹ region and represent excitations of the ν₂₄ (skeletal torsion) and the ν₂₃ (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν₂₃. The A₁/E splitting of the ground vibrational state has been evaluated to be 0.024 cm⁻¹ as it was expected given the high of the methyl torsional barrier (338 cm⁻¹). A very good agreement with respect to previous experimental data concerning fundamental frequencies (ν^CAL − ν^EXP ~ 1 cm⁻¹), and rotational parameters (B₀^CAL − B₀^EXP < 5 MHz), is obtained.

The structural and spectroscopic parameters of dimethyl sulfoxide (DMSO) are predicted from CCSD(T)-F12 calculations that can help to resolve the outstanding problem of the rovibrational spectroscopy. DMSO is a near oblate top that presents a trigonal pyramidal geometry. Rotational parameters are determined at the equilibrium and in selected vibrational states. For the ground state, the rotational constants were calculated to be A₀ = 7031.7237 MHz, B₀ = 6920.1221 MHz, and C₀ = 4223.3389 MHz, at few megahertz from the previous experimental measurements. Ab initio calculations allow us to assert that DMSO rotational constants are strongly dependent on anharmonic effects. Asymmetry increases with the vibrational energy. Harmonic frequencies, torsional parameters, and a two-dimensional potential energy surface (2D-PES) focused to describe the internal rotation of the two methyl groups are determined at the CCSD(T)-F12 level of theory. For the medium and small amplitude motions, anharmonic effects are estimated with MP2 theory getting an excellent agreement with experimental data for the ν₁₁ and ν₂₃ fundamentals. Torsional energies and transitions are computed variationally form the 2D-PES that denotes strong interactions between both internal tops. The vibrationally corrected V₃ torsional barrier is evaluated to be 965.32 cm^–1. The torsional splitting of the ground vibrational state has been estimated to be lower than 0.01 cm^–1. Although the ν₁₃ torsional fundamental is found at 229.837 cm^–1 in good agreement with previous assessment, there is not accord for the low intense transition ν₂₄. A new assignment predicting ν₂₄ to lie between 190 and 195 cm^–1 is proposed.