Journal of Physical Organic Chemistry最新文献

The double-bond isomerization of 1-octene to an equilibrium distribution of all seven linear octene isomers on a dry Amberlyst15 catalyst was followed at 90°C using gas chromatography to resolve five of the seven isomers. The simplest kinetic models that fit observed data over several hours indicated that carbenium ions are likely intermediates in these isomerizations. The C2 octyl carbenium ion appeared to be more stable than the C3 and C4 octyl carbenium ions, leading to a lower equilibrium trans to cis ratio in 2-octene than in 3-octenes and 4-octenes. At equilibrium, [2-octyl carbenium ion] / [3-octyl carbenium ion] = 1.6. The octene adsorption coefficient for double-bond isomerization on this catalyst was 0.4–0.5, indicating a rather weak adsorption. However, the concurrent dimerization of octene to branched hexadecene isomers required an adsorption coefficient of ~40, indicating octene adsorbs onto two different types of sites on this catalyst. The primary alcohol 2-ethyl-1-hexanol was added to reaction mixtures to suppress octene dimerization, and the active isomerization site in this work was a molecule of 2-ethyl-1-hexanol adsorbed onto a supported sulfonic acid group of the initial resin. This new site was less active than the original acid site.

In this article, the structure of the free dicyclopentadiene (DCPD) molecule was studied for the first time by the gas-phase electron diffraction (GED) at 268 K supplemented by quantum chemical calculations (B3LYP and MP2 with the cc-pVTZ basis set). The possibility of transition between endo and exo isomers of DCPD was considered in the gas phase. Three models of the refinement of the experimental (GED) data were applied on the base of two harmonic force fields and molecular dynamic simulations. The theoretical and experimental geometric parameters of the endo isomer are presented. In addition, the geometric parameters of the exo isomer calculated by quantum chemistry are given.

The conductivity of graphene oxide is significantly increases when it is reduced, and oxygen is removed. In this study, the mechanism of deoxygenation of the epoxide sites of small polycyclic aromatic hydrocarbons (PAHs) with triphenylphosphine (PPh₃) was investigated using DFT. When PPh₃ attacks the epoxide oxygen, the carbon–oxygen bond is immediately cleaved by electron transfer, and the oxygen is then abstracted to form triphenylphosphine oxide. The reaction was found to be single-step and different from that of three-membered ring ethers, which are not bound to PAHs. The activation energy for deoxygenation is approximately 20 kcal/mol, and the reaction is exothermic.

Chemical modification of flat graphene surfaces composed of pure sp² carbons is extremely challenging. In this study, we used density functional theory to investigate the addition of phenyl radical derivatives to the surface of graphene flakes and clarified the effect of the nature of the substituents on the activation energy using Hammett plots. Circumcoronene was used as a model for the graphene flakes, and 13 para-substituted phenyl radicals were used as radical species. The activation energy consists of the distortion energies of the graphene flakes and radical species and the interaction energy between the graphene flakes and radical species. The interaction energy is 30%–40% of the activation energy. The interaction energy between the nitrophenyl radical and graphene flake is 3.1 kcal/mol, 2.3 kcal/mol lesser than that between the N,N-dimethylamino-phenyl radical and graphene flake. As the electron-withdrawing properties of the substituents increase, the interaction energy decreases, and consequently, the activation energy decreases. Furthermore, natural energy decomposition analysis shows that the intermolecular interactions are stabilized by charge transfer and electrostatic interactions, the magnitudes of which increase when increasing the Hammett constants of the substituents.

We report on a quantum chemical study (B2PLYP-D3BJ/6-311+G**//B3LYP/6-31+G*) of the mechanism of the reaction of N-allenyl-1H-pyrrole-2-yl-carbaldehydes with hydroxylamine in ethanol leading to pyrrolopyrazine oxides. The main focus is placed on unraveling the influence of the nature of the substituent in the fourth and fifth positions of the pyrrole ring on the kinetic characteristics of the key stages of the reaction, which are oximation and intramolecular cyclization. The aryl substituents are found to favor the reaction, in contrast to the alkyl substituents.

The current understanding of the nature of the physical factors making up the experimentally measured heat capacity change ($��∆�C_P�$) for hydration/solvation occurring with net-neutral solutes at equilibrium in an aqueous solution is based on a large body of experimental work done from 1970 to 2000 which postulates the leading role of the hydrophobic effect (HE) in $��∆�C_P�$. Other contributions have also been identified, but their relative role and nature are not well understood. In the present work, we provide a new insight into the nature of the fundamental terms contributing to $��∆�C_P�$ for a wide variety of molecular processes in an aqueous solution. The crux of our findings is the identification of two leading physical factors, viz., the long known HE and the newly found non-specific solute-solvent van der Waals orientational interactions (Keesom force), making up the magnitude of experimental $��∆�C_P�$ in a general case under the standard conditions of an aqueous solution, “classical” manifestation of HE and employing the model of a rigid net-neutral solute. As a consequence, one can now characterize the thermodynamic nature of various molecular interactions in a solution based on the level of $��∆�C_P�$ from a single viewpoint, including the identification of the leading factor, understanding the interrelation of different factors, the interpretation of the sign of