On the Nature of the CP Bond in Phosphaalkynes

Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach

The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11 kcal·mol(-1)), with barrier heights ranging from 16 to 19 kcal·mol(-1). In contrast, the barrier energies on the keto/enol isomerization are almost 10 kcal·mol(-1) higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed.

The CH3PH2 and CH3PH isomers: isomerization, hydrogen release, thermodynamic, and spectroscopy properties

In this study was performed a quantum chemical investigation of the methylphosphine molecule and its radical, which may show potential implications in interstellar processes, and may be crucial atmospheric tracer gasses in the atmosphere of Giant planets. The analyses were performed with the density functional theory and coupled cluster methods. The anharmonic vibrational modes were predicted for all the isomers. The atomic charge distribution was analyzed with different methodologies and some methods fail to establish the correct sign for phosphorous atom charges. The CH2PH2/CH3PH and CHPH3/CH3PH energy gap is 16.45-17.43 and 67.05-69.02 kcal mol(-1), respectively. The CH2PH3/CH3PH2 energy difference ranges from 44.62 to 50.05 kcal mol(-1). The ionization energy predicted with the W1BD method for CH3PH and CH3PH2 are 8.73 and 9.01 eV, respectively. The heat of formation at 298 K for each molecule were calculated in kcal mol(-1): CH3PH (24.16-25.27), CH2PH2 (41.20-42.47), CHPH3 (92.50-94.23), CH3PH2 (-4.73-2.83) and CH2PH3 (40.03-42.55). The rotational energy barriers for CH3PH2 and CH2PH3 are 1.65 and 2.81 kcal mol(-1), respectively. The CHPH3→CH2PH2 unimolecular arrangement presents a barrier energy of 29.89 kcal mol(-1), whereas CH3PH→CH2PH2 is accessible overcoming a barrier of 42.42 kcal mol(-1). The H2-release routes for CH2PH2 from carbon and phosphorous atoms show a barrier of 98.19 and 46.67 kcal mol(-1), respectively. For the CH3PH2→CH2PH3 isomerization, an energy barrier of 94.00 kcal mol(-1) was predicted, while for the H2-release pathway for CH3PH2 it is necessary to pass a potential energy barrier of 97.56 kcal mol(-1).

Photophysical and excited-state intramolecular proton transfer of 2-(1-(3,5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol: DFT analysis

Fluorescent phenenthrimidazole derivatives have been synthesized and characterized by (1)H, (13)C NMR and mass spectral analyses. Synthesized compounds have been. The solvent effect on the absorption and fluorescence bands has been analyzed and supplement by computational studies. Phenenthrimidazole containing hydroxy group shows a single prominent absorption and emission in polar solvents and dual emission in non-polar solvents due to excited state intramolecular proton transfer (ESIPT). The ESIPT of 2-(1-(3,5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol was cross validated by the analysis of optimized geometry parameters, potential energy surface (PES), mulliken's charge distribution on the heavy atoms and molecular orbitals of its tautomers. Nonviability of ground state electron transfer was explained by HOMO-LUMO analysis. The intramolecular hydrogen bonding (IMHB) interaction has been explored by the calculation of electron density ρ(r) and the Laplacian Δ(2)ρ(r) at the bond critical point (BCP) using atoms-in-molecule (AIM) method and by calculation of hyper conjugative interaction between N17 lone pair and σ*(O53⋯H54) using natural bond orbital (NBO) analysis.

Quantum entanglement in carbon–carbon, carbon–phosphorus and silicon–silicon bonds

We present a quantum entanglement analysis to dissect the bond orders in polyatomic molecules.