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Oxidative addition of aliphatic amine on monocyclic 2‐R‐1,3,2‐dioxaphospholane (R = methyl or phenyl) leading to phosphoranes bearing a PH axial bond was investigated using a combined theoretical and experimental approach. The reaction followed first order kinetics for both reactants. The activation parameters were consistent with a concerted mechanism exhibiting stereo, enantio, and regio specificities. Systematic density functional theory studies including reactivity descriptors, structural parameters, determination of all possible phosphorane isomers, their transition states and their formation mechanisms were carried out to delineate the reaction pathway. Depending on the nature of the atom in the final apical position (H, N of the amine, or C of the methyl), three types of phosphoranes were identified. Energy profiles, using the intrinsic reaction coordinate technique for the formation of each isomer, were established. It was shown that the phosphorus biphilicity acts in three consecutive sequences, namely nitrogen nucleophilic attack leading to a supermolecule structure, nucleophilic behavior of phosphorus in the transition state zone of influence, and electrophilic approach of the nitrogen atom to complete the reaction. Phosphorane with an equatorial PH bond was found to be a kinetic product that transforms rapidly to the thermodynamically stable isomer with axial PH via two consecutive Berry pseudo‐rotations. A new tool, referred to reactive internal reaction coordinates, was introduced to represent the reaction path more clearly. [ABSTRACT FROM AUTHOR]

The SNAr mechanism invoked in this work concerned the substitution reaction of the methoxy group by a secondary amine on the 2-methoxy-5-nitrothiophene and 2-methoxy-3,5-dinitrothiophene molecules. We performed theoretical DFT and TD-DFT calculations. It was examined by theoretical DFT calculations. The hypothesis of a zwitterion formation during the kinetically determining step has been confirmed. However, our calculations have shown that the structure of this reaction intermediate is much more diffuse than commonly accepted. Its geometry can be described as one situation in which the nitrogen of the nucleophilic entity is not totally bound to the carbon, whereas the oxygen of the leaving group prepares to be separated from the substrate. The transition state corresponding to the formation of the zwitterion has a barrier of 17.78 kcal mol−1 in methanol. Three pathways have been studied to describe the second step, leading to the formation of methanol or methoxyammonium. The most probable pathway uses, in a first sequence, a second amine molecule to convert the zwitterion, a dipolar compound, into a hydrogen-bonding association of a carbanion located on the carbon C5 carrying the nitro group and an ammonium with a weak activation barrier of 2.25 kcal mol−1. The electron density supplement provided by the nucleophile is stored at the oxygen atoms of the 5-nitro group in position α of the sulfur atom. The presence of a second nitro group in position β modifies the structure of this carbanion by locating the negative charge on the carbon C3 carrying the second nitro. To visualize the reaction mechanism, we propose an innovative technique called reactive internal reaction coordinate that traces the reaction pathway in a 3D figure as a variation of the energy according to the most active internal coordinates in the transition-state zone of influence. [ABSTRACT FROM AUTHOR]

An investigation of the solid-state X-ray structure of the new organic–inorganic compound [C5H14N2]2PbCl6·3H2O shows a layered organization of the (PbCl6)4– anions, with (R2NH2)+ groups and water molecules developed in the [001] plane at x = (2n + 1)/4. The crystal structure is stabilized by N − H···Cl, N − H···O, O − H···Cl, O − H···O, and C − H···Cl hydrogen bonds. The powder X-ray diffraction and X-ray photoelectron spectroscopic (XPS) analyses confirm the phase purity of the crystal sample. The intermolecular contacts are quantified using the Hirshfeld surfaces computational method. The major inter-contacts contributing to the Hirshfeld surfaces are H...Cl, H...H, and O...H. The vibrational modes were identified and assigned by IR and Raman spectroscopies. The optical properties were investigated by UV–visible and photoluminescence spectroscopic studies. The compound was characterized by thermal analysis to determine its thermal behavior with respect to the temperature. Finally, X-ray photoelectron spectroscopy analysis is reported for analyzing the surface chemistry of [C5H14N2]2PbCl6·3H2O. [ABSTRACT FROM AUTHOR]

Abstract: New poly‐phenylenevinylenes PPVs containing 1,3,4‐thiadiazole as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) and time‐dependent DFT levels. This study has been conducted in order to investigate the geometrical and electronic properties as well as the conductivity of a series of PPV–thiophene–1,3,4–thiadiazole–thiophene (H–PhTAT–H) containing –CHO, –CH2–P(=O)(OCH3)2, and phenyl–CHO (PhCHO) terminal groups. The impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy was studied for different oligomers and for a limit polymer. The incorporation of terminal groups did not affect the chain length evolution and the vertical transition energy Evert value for a polymer limit compared with the unsubstituted oligomer (H–PhTAT–H). All studied properties showed that CHO–PhTAT–PhCHO and H–PhTAT–H oligomers can be considered as n‐type semiconductors. [ABSTRACT FROM AUTHOR]

The quality of predictions of reactivity coming from alternative theoretical approaches as related to the experimental values is examined for the hydrolysis of phenyl N-methylcarbamates. We have combined literature kinetic data for phenyl N-phenylcarbamates with our own kinetic data and have correlated them all with theoretically estimated reactivity indices: i.e. Hirshfeld and NBO atomic charges, the Parr electrophilicity index (ω), and the electrostatic potential at the carbon and oxygen atoms of the reaction centre (VC, VO). The results show that the best correlation coefficients are obtained with the electrostatic potentials VO and VC and the electrophilicity index ω. The variations of electronic structure in the phenolate ions (leaving groups) were also analysed. The results obtained illustrate the accuracy of theoretical description of local properties as provided by the electrostatic potential at the nuclei. [ABSTRACT FROM AUTHOR]

Reaction of the bis(dihydrogen) ruthenium complex RuH2(H2)2(PCy3)2 (1) with an excess of 9-borabicyclononane yields Ru[(μ-H)2BC8H14]2(PCy3) (6) and the phosphine adduct PCy3·HBC8H14. The new complex is characterized by NMR spectroscopy and X-ray diffraction. New X-ray data on 9-BBN dimer, from a measurement at 180 K, are also reported. DFT calculations (B3LYP) on Ru[(μ-H)2BC8H14]2(PMe3) (7), the PMe3 analogue of 6, confirm the ruthenium (II) formulation with two dihydroborate ligands. The data obtained using PH3 or PMe3 as models for PCy3 in PR3·HBC8H14 are also discussed. [Copyright &y& Elsevier]

A unified CO 2 -amine reaction mechanism applicable to absorption in aqueous or nonaqueous solutions and to adsorption on immobilized amines in the presence of both dry and humid conditions is proposed. Key findings supported by theoretical calculations and experimental evidence are as follows: (1) The formation of the 1,3-zwitterion, RH 2 N + -COO - , is highly unlikely because not only the associated four-membered mechanism has a high energy barrier, but also it is not consistent with the orbital symmetry requirements for chemical reactions. (2) The nucleophilic attack of CO 2 by amines requires the catalytic assistance of a Bro̷nsted base through a six-membered mechanism to achieve proton transfer/exchange. An important consequence of this concerted mechanism is that the N and H atoms added to the C=O double bond do not originate from a single amine group. Using ethylenediamine for illustration, detailed description of the reaction pathway is reported using the reactive internal reaction coordinate as a new tool to visualize the reaction path. (3) In the presence of protic amines, the formation of ammonium bicarbonate/carbonate does not take place through the widely accepted hydration of carbamate/carbamic acid. Instead, water behaves as a nucleophile that attacks CO 2 with catalytic assistance by amine groups, and carbamate/carbamic acid decomposes back to amine and CO 2 . (4) Generalization of the catalytic assistance concept to any Bro̷nsted base established through theoretical calculations was supported by infrared measurements. A unified six-membered mechanism was proposed to describe all possible interactions of CO 2 with amines and water, each playing the role of a nucleophile and/or Bro̷nsted base, depending on the actual conditions., Competing Interests: The authors declare no competing financial interest.