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Species generally exhibit one‐state aromaticity either in the lowest singlet state (S0) or the lowest triplet state (T1) according to the Hückel's and Baird's rules. Hence, it is rare for species exhibit two‐state aromaticity in both the S0 and T1 states (termed as adaptive aromaticity), let alone adaptive σ aromaticity. Here, we report adaptive σ aromaticity in unsaturated rhenacyclopropene rings via density functional theory (DFT) calculations. Various aromaticity indices including NICS, ACID, EDDB together with isodesmic reactions support the adaptive σ aromaticity in these rhenacyclopropene rings. As the T1 state of these species is formed by the ππ* excitation, the σ‐aromaticity of these three‐membered rings in the S0 state could hold in the T1 state. In addition, the aromaticity effect of the fused rings is also examined. Our findings expand the family of adaptive σ aromaticity, enriching the metallaaromatic chemistry. [ABSTRACT FROM AUTHOR]

2,6-Dichlorobenzamide (BAM), 2-(trifluoromethyl)benzamide (TBAM), 2-(trifluoromethyl)benzoic acid (TBA), and 3-chloro-5-(trifluoromethyl)pyridine-2-carboxylic acid (PCA) are degradation by-products of fluopicolide and fluopyram fungicides. In this work, a detailed theoretical study of their different molecular, spectroscopic and thermochemical properties was carried out with different formulations of the density functional theory and high-level model chemistries. The mean values of −146.0 ± 6.3, −763.2 ± 6.3, −949.0 ± 6.3, and −919.4 ± 6.3 kJ mol−1 for the standard enthalpies of formation of BAM, TBAM, TBA and PCA, respectively, were derived for the first time at the G3MP2//DFT and G4MP2//DFT levels of theory (DFT = B3LYP, BMK, and B98). Additionally, a good agreement between formation enthalpies derived from isodesmic reaction approach and from Benson's group additivity method was obtained. [ABSTRACT FROM AUTHOR]

5‐amino‐3‐nitro‐1‐nitramino‐1,2,4‐triazole was synthesized through the nitration reaction of 1,5‐diamino‐3‐nitro‐1,2,4‐triazole, and several energetic salts were prepared based on the reactivity of the acidic proton in nitramino group (−NHNO2). These compounds were fully characterized by NMR (1H and 13C), IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. Their thermal stabilities were analyzed by differential scanning calorimetric (DSC) and Impact and friction sensitivities were determined using standard BAM technology. Moreover, the structural differences between individual compounds were studied to investigate the potential structure‐property relationship. All compounds possess positive heats of formation calculated based on isodesmic reaction to be between 173.7~454.6 kJ ⋅ mol−1. Among them, 5‐amino‐3‐nitro‐1‐nitramino‐1,2,4‐triazole (D=8682 m ⋅ s−1, P=33.0 GPa, IS=0.75 J), hydrazine salt (D=8908 m ⋅ s−1, P=34.9 GPa, IS=0.5 J) and hydroxylamine salt (D=9117 m ⋅ s−1, P=36.7 GPa, IS=2 J) exhibits desirable detonation properties similar to RDX (D=8795 m ⋅ s−1, P=34.9 GPa), calculated by Kamlet‐Jacobs equations and features comparable impact sensitivity with DDNP (IS=1 J). The simple synthetic route, free of heavy metals and superior detonation properties of above compounds make them serve as promising candidate for green primary explosives. [ABSTRACT FROM AUTHOR]

Phosphine oxides and arsine oxides feature highly polarized pnictoryl groups (Pn+–O−/Pn = O; Pn = P, As) and react as Brønsted bases through O-centered lone pairs. We recently reported the first example of a monomeric stibine oxide, Dipp3SbO (Dipp = diisopropylphenyl), allowing periodic trends in pnictoryl bonding to be extended to antimony for the first time. Computational studies suggest that, as the pnictogen atom becomes heavier, delocalization of electron density from the O-centered lone pairs to the Pn–C σ* orbitals is attenuated, destabilizing the lone pairs and increasing the donor capacity of the pnictine oxide. Herein, we assess the Brønsted basicity of a series of monomeric pnictine oxides (Dipp3PnO; Pn = P, As, and Sb). Stoichiometric reactivity between Dipp3PnO and a series of acids demonstrates the greatly enhanced ability of Dipp3SbO to accept protons relative to the lighter congeners, consistent with theoretical isodesmic reaction enthalpies and proton affinities. 1H NMR spectrometric titrations allow for the pKaH,MeCN determination of Dipp3AsO and Dipp3SbO, revealing a 106-fold increase in Brønsted basicity from Dipp3AsO to Dipp3SbO. The increased basicity can be exploited in catalysis; Dipp3SbO exhibits dramatically increased catalytic efficiency in the Brønsted base-catalyzed transesterification between p-nitrophenyl acetate and 2,2,2-trifluoroethanol. Our results unambiguously confirm the drastic increase in Brønsted basicity from Dipp3PO < Dipp3AsO < Dipp3SbO, a direct consequence of the variation in the electronic structure of the pnictoryl bond as the pnictogen atom increases in atomic number. [ABSTRACT FROM AUTHOR]

The wide availability, ease of handling and structural and functional diversity make carboxylic acids prized building blocks in organic synthesis. The past two decades has seen an explosion of interest in the development of new modes of reactivity of carboxylic acids and their derivatives. Of these, metal‐mediated decarboxylation reactions are attractive as they produce organometallic intermediates that can subsequently be used in C−X (where X=C, N, S etc) bond coupling reactions. Here the results of mechanistic studies integrating both gas‐ and condensed‐phase work are described for development of new extrusion‐insertion (ExIn) classes of reactions for the synthesis of amides, thioamides, amidines, alkenes and ketones from arylcarboxylic acids and suitable (hetero)cumulenes. [ABSTRACT FROM AUTHOR]

Density functional theory studies have been performed on a series of highly substituted imidazole and indole derivatives. Heats of formation have been calculated using B3LYP functional with 6-31G basis sets by designing isodesmic reaction conditions. General trend which has been observed in the case of highly substituted imidazoles is that as substitution increases the heat of formation increases. The HOF of 1,2,4,5-tetraphenyl-1H-imidazole is the largest (131.28 kJ/mol) and the HOF of 2-(4-chlorophenyl)-1-benzyl-4,5-diphenyl-1H-imidazole (H) is the smallest (85.82 kJ/mol) at the B3LYP/6-31G level. The relative stability of the substituted imidazoles have been evaluated based on the calculated HOFs and the energy gap between the frontier molecular orbitals. [ABSTRACT FROM AUTHOR]

Addition of anhydrous HF to the hydrochloride [MeCAACH][Cl(HCl)0.5] resulted in the formation of salts with high HF content. By stepwise removal of HF in vacuo, we selectively prepared [MeCAACH][F(HF)2] (3) and [MeCAACH][F(HF)3] (4). We also characterised a salt with [F(HF)4]− anions within the structure of [MeCAACH][F(HF)3.5] (5). Compounds with a lower content of HF were not accessible under vacuum conditions. MeCAAC(H)F (1) was selectively prepared by abstraction of HF from 3 with CsF or KF, while [MeCAACH][F(HF)] (2) was prepared by mixing 3 and 1 in a 1 : 1 ratio. Compound 2 proved to be quite unstable as it tends to disproportionate into 1 and 3. This observation triggered our computational study, in which the structural relationships between CAAC-based fluoropyrrolidines and dihydropyrrolium fluorides were investigated using different DFT methods. The study showed that the results were very sensitive to the computational method used. For a correct description, the quality of the triple-ζ basis set was crucial. Surprisingly, the isodesmic reaction of [MeCAACH][F] + [MeCAACH][F(HF)2] → [MeCAACH][F(HF)] + [MeCAACH][F(HF)] did not confirm the low thermodynamic stability of 2. Furthermore, the use of 3 as a nucleophilic fluorinating reagent was tested on a range of organic substrates, as it is the most stable compound in this series. It was found to have the potential to fluorinate benzyl bromides, 1- and 2-alkyl bromides, silanes and sulfonyls with good to excellent yields of the target fluorides. [ABSTRACT FROM AUTHOR]

The open‐source statistical mechanics software described here, Arkane–Automated Reaction Kinetics and Network Exploration–facilitates computations of thermodynamic properties of chemical species, high‐pressure limit reaction rate coefficients, and pressure‐dependent rate coefficient over multi‐well molecular potential energy surfaces (PES) including the effects of collisional energy transfer on phenomenological kinetics. Arkane can use estimates to fill in information for molecules or reactions where quantum chemistry information is missing. The software solves the internal energy master equation for complex unimolecular reaction systems. Inputs to the software include converged electronic structure computations performed by the user using a variety of supported software packages (Gaussian, Molpro, Orca, TeraChem, Q‐Chem, Psi4). The software outputs high‐pressure limit rate coefficients and pressure‐dependent phenomenological rate coefficients, as well as computed thermodynamic properties (enthalpy, entropy, and constant pressure heat capacity) with added energy corrections. Some of the key features of Arkane include treatment of 1D, 2D or ND hindered internal rotation modes, treatment of free internal rotation modes, quantum tunneling effect consideration, transition state theory (TST) and Rice‐Ramsperger‐Kassel‐Marcus (RRKM) rate coefficient computations, master equation solution with four implemented methods, inverse‐Laplace transform of high‐pressure limit rate coefficients into the energy domain, energy corrections based on bond‐additivity or isodesmic reactions, automated and efficient PES exploration, and PES sensitivity analysis. The present work describes the design of Arkane, how it should be used, and refers to the theory that it employs. Arkane is distributed via the RMG‐Py software suite (https://github.com/ReactionMechanismGenerator/RMG‐Py). [ABSTRACT FROM AUTHOR]

Isodesmic reactions represent mild alternatives to other chemical transformations that require harsh oxidizing agents or highly reactive intermediates. However, enantioselective isodesmic C−H functionalization is unknown and enantioselective direct iodination of inert C−H bond is very rare. Rapid synthesis of chiral aromatic iodides is of significant importance for synthetic chemistry. Herein, we report an unprecedented highly enantioselective isodesmic C−H functionalization to access chiral iodinated phenylacetic Weinreb amides via desymmetrization and kinetic resolution with PdII catalysis. Importantly, further transformations of the enantioenriched products are readily available at the iodinated or the Weinreb amide position, paving the way of related studies for synthetic and medicinal chemists. [ABSTRACT FROM AUTHOR]

Accurate thermochemical data of SixHy and SixFy series is a prerequisite for high‐end materials design. In this study, the standard enthalpies of formation (∆fHθ) of SixHy and SixFy were calculated from atomization and isodesmic reactions using the composite methods CBS‐QB3, G3, G4, W1U, W1BD, and W2‐F12. Second, their temperature‐dependent thermochemical parameters (∆푓푆θ and Cp) are derived from the optimized geometries and frequency calculation at B3LYP/cc‐pV(T + d)Z level. In addition, this paper uses nonexpert‐user methods (CBS‐QB3, G3, G4, W1U and W1BD) to compare the calculated ∆fHθ with recommended values of Active Thermochemical Table, Burcat database, and W2‐F12 calculation results. The accuracy of these nonexpert‐user methods are interpreted in terms of descriptive statistics. The results show that: (1) the accuracy rank of individual compound methods is as follows: CBS‐QB3 > W1BD > W1U > G4 > G3; (2) for Si/H/F compounds, three combination methods, CBS‐QB3/G4/W1U or CBS‐QB3/G4/W1BD, and two combination methods, G4/W1U or G4/W1BD, were quite powerful, and the weighted results could reproduce the recommended values within "near‐chemical‐accuracy," (3) the popular W1BD and W1U methods give highly erroneous results, indicating that one should not apply these methods in isolation unless other error‐cancellation strategies are collocated indicated. [ABSTRACT FROM AUTHOR]

• Δ f H gas ° for 2- and 8-hydroxy azaazulene and their mercapto analogues were estimated at B3LYP, M06-2X, and G3MP2 levels. • Δ f H gas ° is calculated using atomization and isodesmic reactions. • ketonization/thionization is thermodynamically preferred process. • PA, GB, and DPE for studied structures were calculated at three levels of calculation. • Transfer a proton from keto/thione form is not a preferred process. The gas phase standard enthalpies of formation Δ f H gas ° for the tautomers and rotamers of 2- and 8-hydroxy azaazulene and their mercapto analogues have been estimated at B3LYP/6–311 + G(d,p) and M06-2X/6–311++G(2d,2p) levels of theory. The G3MP2 composite method has also been utilized to obtain more accurate correlated computational results. By using atomization and isodesmic reactions, it has been possible to calculate the theoretical enthalpies of formation for the structures under study. Depending on the enthalpies of formation results, the stability of the examined tautomers and rotamers has been discussed. The gas-phase basicity (GB), proton affinities (PA) of the N and O/S atoms, and the deprotonation enthalpies (DPE) of the NH and OH/SH bonds for the investigated system have been determined at the three levels of theory as well. [ABSTRACT FROM AUTHOR]

Large π-π Separation Energies of azafullerene. C 48 N 12 (xiii) +12 NH 3 +24 CH 4 →6 C 8 H 6 N 2 (xiii)+12 CH 3 NH 2 + 6 CH 3 CH 3. C 48 N 12 (xiv) +12 NH 3 +24 CH 4 →6 C 8 H 6 N 2 (xiv)+12 CH 3 NH 2 + 6 CH 3 CH 3. E π - π = ∑ i (ν i E 0 , i + ν i Z P E i) [Display omitted] • A method for calculating the large π – π separation energy for aza fullerene is provided. • Large π − π separation energies were calculated for fullerene-like C48N12-like and C24N36 derivatives. • Large π − π separation energy is a new theoretical concept, an extension of aromaticity. The stability of green, high-energy and high-nitrogen compounds has always been the focus of our attention.The large π-π interconnected structures of fullerene C 60 and its aza derivatives C 48 N 12 and C 24 N 36 and their separation methods were established.This method can directly reflect the structural characteristics of fullerene C 60 and its aza derivatives and the arrangement of atoms in space.The large π-π separation energies have been calculated at WB97XD/DEF2TZVP level with high accuracy by using equal bond reaction design.The higher the large π-π separation energy, the more stable the molecular structure. The large π-π separation energy is related to the aromaticity of compounds. As the concept of aromaticity is constantly developing and updated, the connotation of large π-π separation energy will also have new development. The concept and calculation method of large π-π separation energy can be applied to other non-energetic large π-π interconnected structures. [ABSTRACT FROM AUTHOR]

A set of C2-chiral bases with bis-protonation sites (1–9) on dimethyl-binaphthalene derivatives have been explored using the B3LYP/6-311+G(d,p) level and the proton affinities calculated are in the range of superbases for both the sites. This would be the first report to possess a basicity exceeding the range of superbases on either basic site. The pKa predicted for the designed system (9) in acetonitrile comes in the range of 32–36 at the B3LYP/6-311+G(d,p) level. The molecular electrostatic isopotential surface (MESP) shows that the two basic sites can simultaneously be protonated and the average PA results are also in the superbase region. The isodesmic reactions suggest that the super basicity achieved in these cases is the interplay of the ring strain of unprotonated bases, the steric repulsion, and the strength of intramolecular hydrogen bonding interactions. The kinetic activity predicted from the proton transfer study suggests that such chiral bases can perform as potential catalysts. [ABSTRACT FROM AUTHOR]

Nitro-substituted derivatives of indole were designed by substituting the hydrogen atoms of indole one by one. To explore the thermal stability, the heats of formation were calculated by using the isodesmic reaction and positive values are confirmed for all of them, which indicated their energetic nature. To explore the kinetic stability, the bond dissociation energies are calculated accompanied by the bond orders, and enough kinetic stability is evaluated. To detect the potential application as high-energy-density compounds, the detonation velocity (D), the detonation pressure (P), the explosive heats (Q), and the molecular density (ρ) is calculated further according to the famous Kamlet-Jacobs equation. Based on our calculation, hex-substituted indole has excellent detonation characters (D = 8.80 km/s, P = 35.88 GPa) and can be regarded as high-energy-density compounds for further research. [ABSTRACT FROM AUTHOR]

The ability of three semiempirical methods (PM3, PM5, and PM7) in reproducing the enthalpy of formation (ΔfH°) of polycyclic aromatic phenols (PAPs) was tested by comparing experimental and calculated values for 33 compounds. In addition, the results from the semiempirical methods were compared to those obtained from the suitable isodesmic reactions, performed using the B3LYP–D3 and M06–2X functionals in combination with the 6-311 + G(d,p) basis set. With an average absolute error less than 10 kJ mol−1, all five methodologies yielded mutually comparable results. Considering low computational cost of semiempirical methods, the influence of structural features on ΔfH° of PAPs was investigated using the PM5 and PM7 methods. It was found that the greatest influence on ΔfH° has the size of the molecules, while the effects of other properties, i.e., the position of the OH group, number of bay regions, and molecular branching are weaker. The influence of the OH group position decreases with its moving away from molecular ends, and eventually becomes insignificant. As branching and the number of bay regions are mutually dependent and respective molecules are often nonplanar, it is difficult to examine individual contributions of these two structural features. In general, ΔfH° decreases with increasing number of bay regions and molecular branching. [ABSTRACT FROM AUTHOR]

The discovery and preparation of important molecules rely on the synthetic chemist's ability to valorize common feedstock materials, such as petroleum or biomass. Key to this endeavor is the design of efficient methods to introduce, remove or interconvert functional groups. Our group has a longstanding interest in developing conceptually novel catalytic reactions for the installation of unprotected amines, the selective activation of C–O bonds (in polyols) and the transfer (shuttle) or exchange (metathesis) of functionalities between two molecules. This account describes representative examples from our group in these different research areas.

Cyclododecane preferentially adopts a square‐like geometry, giving rise to corner and edge methylene (CH2) groups, whose hydrogens assume different orientations. In edge CH2 groups, hydrogens can be inward‐ (endo) and outward‐looking (exo) the ring. Herein, we have quantum‐chemically studied the replacement of two hydrogens in cyclododecane with iodines at the relative positions 1,4, 1,5, 1,6, and 1,7. Intramolecular interactions are only slightly unfavorable in 1,7‐diiodocyclododecane containing the organic iodines in the edge/endo positions, less than expected from steric considerations. This behavior was discussed in terms of transannular interactions, and a numerical estimation for the magnitude of the intramolecular interaction energy has been performed based on an isodesmic reaction scheme and by natural energy decomposition analysis. 1,5‐Diiodocyclododecane with both edge iodines in the endo orientation (occupying opposite faces of the ring) is strongly favored (by ca. 2.0 kcal mol−1) compared to the respective monosubstituted counterparts, due to highly stabilizing hyperconjugative interactions. Although halogen bonding involving anionic species is widely known, we show that organic halogens, in particular iodine, can be useful for stereochemical control in macrocycles. [ABSTRACT FROM AUTHOR]

The effects of nitrogen substituent on stability (ΔΕs–t) of novel germylenes with one, two, and three germylene centers are compared and contrasted at B3LYP/6‐311++G** level of theory. These singlet and triplet germylenes (1s–18s and 1t–18t, respectively) appear as minimum on its energy surface, and the order of their stability estimated by singlet (s)–triplet (t) energy difference (ΔEs–t = Et − Es) is 16 > 6 > 1 > 15 > 17 > 2 > 8 > 3 > 9 > 11 > 7 > 10 > 12 > 14 > 5 > 4 > 18 > 13. Hence, every singlet germylene shows more stability than its corresponding triplet. Germylene 13 with the lowest stability (ΔEs–t = 4.31 kcal/mol) has the highest nucleophilicity (4.47 eV). Applying suitable isodesmic reactions, we show that the σ‐acceptor nitrogen substituents stabilize not only the singlet but also the triplet states with their positive ΔE. The aim of the present work is to recognize the influence of nitrogen and germylene centers on the stability and band gap (ΔΕHOMO–LUMO), electrophilicity (ω), nucleophilicity (N), and etc. They can be used as accumulated multidentate ligands. [ABSTRACT FROM AUTHOR]

Various 1,2,5-oxadiazole-1,2,3,4-tetrazole-based high-energy materials were designed and their properties investigated. Their heat of formation, detonation properties, and thermal stability were calculated on the basis of isodesmic reactions, Kamlet-Jacobs equation, and bond dissociation energy, respectively. The results showed that all designed compounds possess high positive heat of formation, and the –N=N–/–N3 substituents were found to be the most effective for improving the heat of formation. The trend of changes in density, detonation pressure, and detonation velocity was almost identical in all compounds, which suggests that density was key to the determination of detonation properties. In view of bond dissociation energy, the –CN/–NH2 substituents improved the thermal stability of the designed compounds, while the other substituents/bridges decreased the stability to some extent. Considering the detonation properties and thermal stability, six compounds (C7, D3, D7, F7, G7, and H7) were selected as potential high-energy materials because they exhibited higher detonation properties and thermal stability than 1,3,5-trinitro-1,3,5-triazinane (RDX). Finally, electronic structures (such as distribution of frontier molecular orbitals and electrostatic potential) of the selected compounds were simulated to obtain detailed information about the electronic structures of the screened compounds. [ABSTRACT FROM AUTHOR]

The effective charges on hydrogen and carbon atoms and the Fukui functions for the electrophilic and radical attacks for the hydrogen atoms of the chair and boat conformations of cyclohexanone were calculated using the density functional theory (DFT) with the hybrid functionals: B3LYP in the 6-311g++(d,p) basis set; X3LYP in the 6-311g++(d,p) and D95++(d,p) basis sets; and pbe1pbe in the D95++(d,p) basis set, and by the MP2 method in the 6-311g++(d,p) basis set. For these conformations, the transition states were localized; the length of the broken CH bond in the transition state was determined; and the activation energies, activation entropies, and enthalpies of the elementary reactions of the tert-butylperoxyl ((СН3)3СOO•) radical with all types of CH bonds of cyclohexanone were calculated. The relative reactivity of the CH bonds of cyclohexanone in reactions with ((СН3)3СOO•); the local electrophilicity indices of the carbon-centered radicals formed from cyclohexanone after elimination of the hydrogen atom; and the energy difference (ΔЕSOMO) between the single-occupied molecular orbitals of these carbon-centered radicals and the (СН3)3СOO• radical were calculated. The CH bond dissociation energies of cyclohexanone were calculated by the DFT B3LYP 6-311g++(d,p), CBS-QB3, and G3MP2B3 methods using the isodesmic reactions technique. The factors governing the CH bond reactivity of cyclohexanone in reactions with the (СН3)3СOO• radical were considered. The increased reactivity of CH bonds of cyclohexanone in the 2, 6 (α) positions was shown to be due to the low bond dissociation energy, high electron-donor capacity of hydrogen atoms, smaller length of the broken CH bond in the transition state, and small ΔЕSOMO value. The lower reactivity of CH bonds at positions 3, 5 (β), and 4 (γ) is determined by the higher bond dissociation energies, decreased electron density due to the inductive effect of the carbonyl group, nucleophilicity of the carbon-centered radicals, greater length of the broken CH bonds in the transition state, and larger ΔЕSOMO value. The difference in the reactivity of CH bonds at positions 3, 5 (β), and 4 (γ) is determined by these factors, but not by the difference in the dissociation energies of these bonds. The reactivity of CH bonds in the boat conformation is higher than that in the chair conformation in the reactions with the (СН3)3СOO• radical. [ABSTRACT FROM AUTHOR]

The physicochemical properties of a drug molecule determine the therapeutic effectiveness of the drug. Thus, the development of fast and accurate theoretical approaches for the prediction of such properties is inevitable. The participation to the SAMPL7 challenge is based on the estimation of logP coefficients and pKa values of small drug-like sulfonamide derivatives. Thereby, quantum mechanical calculations were carried out in order to calculate the free energy of solvation and the transfer energy of 22 drug-like compounds in different environments (water and n-octanol) by employing the SMD solvation model. For logP calculations, we studied eleven different methodologies to calculate the transfer free energies, the lowest RMSE value was obtained for the M06L/def2-TZVP//M06L/def2-SVP level of theory. On the other hand, we employed an isodesmic reaction scheme within the macro pKa framework; this was based on selecting reference molecules similar to the SAMPL7 challenge molecules. Consequently, highly well correlated pKa values were obtained with the M062X/6–311+G(2df,2p)//M052X/6–31+G(d,p) level of theory. [ABSTRACT FROM AUTHOR]

We have scrutinized eighteen new derivatives of carbenes with one, two, and three carbenic centers and compared their structural and thermodynamic parameters, at B3LYP/6-311++G** level of theory. All novel carbene scrutinized show singlet ground stat, and the highest stability belongs to 1,2,3,4-tetraazabicyclo[1.1.1]-5-pentanylene (9) (ΔEs-t = 47.95 kcal/mol). This stability can be related to their σ−bond and intermolecular interactions. This bond arose from a tendency of nonbonding electrons of nitrogen (N(E or G)) to empty p orbital of the carbenic center. In addition, carbene 16s and 17s because of three coordinate covalent bonds with their carbenic centers have low nucleophilicity (N). The increase in band gaps (ΔΕHOMO–LUMO) is correlated with an increase in ΔΕs–t values. The purpose of the present work was to assess the influence of 1 to 4 nitrogen substituents on the stability (ΔEs-t), ΔΕHOMO–LUMO, N, electrophilicity (ω), and isodesmic reactions. Finally, our investigation introduces novel carbenes that can be applied as cumulated multi-dentate ligands. [ABSTRACT FROM AUTHOR]

Polyoxymethylene dimethyl ether (PODE n) is a promising fuel additive to reduce soot emissions. In this work, a theoretical study on the H-abstraction reaction from PODE 2 (CH 3 OCH 2 OCH 2 OCH 3) by the H atom and CH 3 radical, as well as the subsequent isomerization and β-dissociation reactions of PODE 2 radicals were carried out. The geometry optimization and frequency analysis for all the stationary points on the potential energy surfaces (PESs) were performed at the M08-HX/6-311+G(2df,2p) level of theory. Single point energies were calculated using the CCSD(T)-F12 method together with the cc-pVTZ basis set. The high-pressure limit rate constants of the H-abstraction reactions from PODE 2 were determined through the multistructural canonical variational transition state theory (MS-CVT) with small-curvature tunneling (SCT) correction. The temperature and pressure dependent rate constants for the unimolecular reactions of radicals produced by the H-abstraction reactions from PODE 2 were calculated by solving the energy-dependent master equation using the Tsinghua University Minnesota Master Equation (TUMME) program. For the H-abstraction channels of PODE 2 , reaction pathways initiated via H atom attack are more energetically and kinetically favored over those via CH 3 radical within the studied temperature range. The PODE 2 radicals with H atoms abstracted from CH 3 and CH 2 sites are denoted as PODE2A (CH 3 OCH 2 OCH 2 OCH 2) and PODE2B (CH 3 OCH 2 OCHOCH 3), respectively. For unimolecular reaction channels of PODE2A radical, with increased temperatures, the dominant reaction shifts from isomerization to the decomposition process. In the case of the PODE2B radical, the two decomposition channels are consistently preferred across all temperature ranges, resulting in a competitive relationship between them. The thermodynamic properties of PODE 2 and its associated radicals were calculated using the isodesmic reaction method in conjunction with multistructural torsional partition functions. Based upon the newly calculated rate constants and existing literature models, an updated kinetic model describing PODE 2 combustion chemistry is developed in this work. This model incorporates the latest findings and contributes to a more comprehensive understanding of the oxidation and auto-ignition characteristics of PODE 2. [ABSTRACT FROM AUTHOR]

The DLPNO-CCSD(T1)/CBS and G4 methods combined with isogyric, isodesmic, and homodesmotic working reactions were applied to calculate gas-phase enthalpies of formation for thirty-three C–H–N–O compounds with well-established experimental values. Unlike the G4 method, the DLPNO calculations, even together with isogyric reactions with small reference species, reproduce the experimental enthalpies of formation within chemical accuracy (≈ 4 kJ/mol). For more than half of the compounds, a better accuracy, within 2 kJ/mol, was achieved. These results make the DLPNO-CCSD(T1)/CBS method a promising tool for accurate prediction of enthalpy of formation of medium-sized organic compounds. Being convinced of its reliability, the DLPNO-CCSD(T1)/CBS method was also used to estimate the enthalpies of formation for some challenging compounds with conflicting values reported in the literature (glycerol, nitromethane, nitrobenzene, 1-aminoadamantane, piperazine, and others). [ABSTRACT FROM AUTHOR]

Following our quest for stable group 14 divalents, novel N-heterocyclic plumbylenes (NHPbs), composed of 2,4,6-cycloheptatriene-2,7-diazaplumbylene (1), benzannulated with one (2), two (3, 4), and three benzene rings (5), are compared and contrasted at the density functional theory level. Results indicate that in going from 1 to 5, the absolute values of singlet-triplet energy gap (ΔEs-t) and band gap (ΔEH-L) increase, while nucleophilicity (N), electrophilicity (ω), and chemical potential (μ) decrease. The most benzannulated structure, ([a,c,e]tribenzo)cyclohepta-2,7-diazaplumbylene (5), turns out as the most stable plumbylene for showing the most negative ΔEs-t of − 194.94 kcal/mol. Furthermore, 5 shows the highest ΔEH-L (− 2.75 eV), with the lowest N (1.31 eV), ω (8.20 eV), μ (− 7.15 eV), and charge of (+ 0.736) on Pb atom. Isodesmic reactions of 1-5 with common transition metal halides, MX2, give forty new metal complexes of 1M-X-5M-X, where M = Pt and Pd, while X = F, Cl, Br, and I. Their complexation energies (ΔECom) indicate that 1-5 are rather stronger ligands with Pt than Pd. Bader's atoms in molecules (AIM) and NBO analyses show the partial covalent and partial electrostatic nature of Pb-M bonds. [ABSTRACT FROM AUTHOR]

Recently, we found less nucleophilicity (N) for normally and abnormally disubstituted Arduengo‐type monosilylenes [R2N4Si:] (1–10) than their corresponding disilavinylidene ligands [R2N4SiSi:] (1′–10′). Considering the importance of silylene–iron complexes, here we compare and contrast thermodynamic properties of their novel [R2N4Si: → Fe(N(SiH3)2)2] (1c–10c) and [R2N4SiSi: → Fe(N(SiH3)2)2] iron complexes (1′c–10′c), for R = H, Me, ethyl, i‐propyl, and t‐butyl, at B3LYP/6‐311++G**+ LANL2DZ level of theory. Isodesmic reactions show higher stability for disilavinylidenes 1′c–10′c compared with their corresponding monosilylene 1c–10c. In all species, the natural bond orbital (NBO) calculations show transfer of charge from the silylene (of the ligand) to iron(II). Multiple Fe–Si bonding character is detected in all complexes (Wiberg bond index > 1). Yet Fe–Si bond distances in 1′c–10′c appear shorter than those in their corresponding 1c–10c. Binding energy (ΔEbin) of [Fe(N(SiH3)2)2] with 1′–10′ appears higher in 1′c–10′c than the corresponding 1c–10c. [ABSTRACT FROM AUTHOR]

A computational study on the molecular structure, harmonic vibrational frequencies and thermochemical parameters of the postulated intermediates and final products involved in the gas-phase pyrolysis of (c-C3H5)NH2 (CPA) has been carried out by ab-initio and DFT methods. Internal rotor potentials were determined employing CAS-MP2 calculations for the singlet ĊH2CH2ĊHNH2 biradical and DFT for singlet CH3CH2C̈NH2,cis- and trans-CH3CH=CHNH2, E- and Z-CH3CH2CH=NH, (c-C3H5)NHCH(NH2)CH2CH3, E- and Z-(c-C3H5)N=CHCH2CH3. The enthalpies of formation at 0 and 298 K for these species were derived from isodesmic reactions using the B3LYP and M06-2X functionals coupled to the 6-311++G(3df,3pd) basis set and ab-initio G3(MP2) and G3(MP2)//B3LYP/6-311++G(3df,3pd) composite models. At the last level, enthalpies of formation at 298 K of 69.94 and 40.37 kcal mol−1 were estimated for the first time for ĊH2CH2ĊHNH2 and CH3CH2C̈NH2, and values of 7.28, 8.12, 5.37 and 6.08 kcal mol−1 were derived for cis-CH3CH=CHNH2, trans-CH3CH=CHNH2, E-CH3CH2CH=NH and Z-CH3CH2CH=NH, respectively. Accordingly, the pyrolysis of CPA to give ĊH2CH2ĊHNH2 and CH3CH2C̈NH2 is predicted to be endothermic by 51.58 and 22.01 kcal mol−1, whereas all other reaction steps are exothermic. For the overall reaction, 2 CPA → (c-C3H5)N=CHCH2CH3 + NH3, a standard change in enthalpy of about −20 kcal mol−1 was obtained. [ABSTRACT FROM AUTHOR]

We present a systematic assessment of the density functional tight binding (DFTB) method for calculating heats of formation of fullerenes with isodesmic‐type reaction schemes. We show that DFTB3‐D/3ob can accurately predict ΔfH values of the 1812 structural isomers of C60, reproduce subtle trends in ΔfH values for 24 isolated pentagon rule (IPR) isomers of C84, and predict ΔfH values of giant fullerenes that are in effectively exact agreement with benchmark DSD‐PBEP86/def2‐QZVPP calculations. For fullerenes up to C320, DFTB ΔfH values are within 1.0 kJ mol−1 of DSD‐PBEP86/def2‐QZVPP values per carbon atom, and on a per carbon atom basis DFTB3‐D/3ob yields exactly the same numerical trend of (ΔfH [per carbon] = 722n−0.72 + 5.2 kJ mol−1). DFTB3‐D/3ob is therefore an accurate replacement for high‐level DHDFT and composite thermochemical methods in predicting of thermochemical stabilities of giant fullerenes and analogous nanocarbon architectures. [ABSTRACT FROM AUTHOR]

A combinatorial approach was applied to devise a set of reference Si–C–O–H species that is used to derive group‐additivity values (GAVs) for this class of molecules. The reference species include 62 stable single‐bonded, 19 cyclic, and nine double‐bonded Si–C–O–H species. The thermochemistry of these reference species, that is, the standard enthalpy of formation, entropy, and heat capacities covering the temperature range from 298 to 2000 K was obtained from quantum chemical calculations using several composite methods, including G4, G4MP2, and CBSQB3, and the isodesmic reaction approach. To calculate the GAVs from the ab initio based thermochemistry of the compounds in the training set, a multivariable linear regression analysis is performed. The sensitivity of GAVs to the different composite methods is discussed, and thermodynamics properties calculated via group additivity are compared with available ab initio calculated values from the literature. [ABSTRACT FROM AUTHOR]

In this study, based on two attractive energetic compounds pentazole (PZ) and tetraazacubane (TAC), a new family of high energy and high nitrogen compounds pentazolyltetraazacubanes were designed. Then, a different number of NH2 or NO2 groups were introduced into the system to further adjust the property. The structures, properties, and the structure-property relationship of designed molecules were investigated theoretically. The results showed that all nine designed compounds have extremely high heat of formation (HOF, 1226-2734 kJ/mol), good density (1.73e1.88 g/cm3), high detonation velocity (8.30e9.35 km/s), high detonation pressure (29.8e39.7 GPa) and acceptable sensitivity (ΔV: 41-87 Å3). These properties could be effectively positive adjusted by replacing one or two PZ rings by NH2 or/and NO2 groups, especially for the energy and sensitivity performance, which were increased and decreased obviously, respectively. As a result, two designed pentazolyltetraazacubanes were predicted to have higher energy and lower sensitivity than the famous high energy compound in use 1,3,5,7-tetranitro- 1,3,5,7-tetraazacyclooctane, while two others have better combination property than 1,3,5-Trinitro-1,3,5- triazacyclohexane. In all, four new pentazolyltetraazacubanes with good combination performance were successfully designed by combining PZ with TAC, and the further property adjustment strategy of introducing a suitable amount of NH2/NO2 groups into the system. This work may help develop new cage energetic compounds. [ABSTRACT FROM AUTHOR]

Two closely related compounds, namely, O-methyl (4-fluorobenzoyl)carbamothioate (I) and O-methyl (4-methylbenzoyl)carbamothioate (II) were prepared in good yields by the reaction of the corresponding benzoyl isothiocyanates and methanol. The structural and conformational properties of both compounds were analyzed using a combined approach including single-crystal X-ray diffraction and quantum chemical calculations. A rich conformational landscape is envisaged for the vacuum-isolated species around the central carbamothioate group, with the pseudo-anti conformation (C＝O and C＝S double bonds pointing toward opposite orientations) being the most stable form. The X-ray molecular structure shows the presence of this form in the crystalline phase for both compounds. The occurrence of a 1,5-O⋯O intramolecular short distance was observed, suggesting the relevance of chalcogen⋯chalcogen interactions in the conformational preference. Natural bond orbital population analysis and quantum chemical calculations through an isodesmic reaction scheme were applied to better understand the conformational preference and the nature of the O⋯O intramolecular interactions. The quantum theory of atoms in molecules was also used to examine the electronic densities around the S(5) pseudo-ring formed through the intramolecular interaction in the carbamothioate moiety. Furthermore, the vibrational features were analyzed by measuring the infrared and Raman spectra. [ABSTRACT FROM AUTHOR]

Si–C–H-containing radicals and stable species are present in the oxidation of silicon-organic compounds such as methyl and ethyl silanes, which are frequently-used precursors for the synthesis of silicon-based nanoparticles and coatings via combustion processes. Silicon-containing intermediates interact with flame radicals and thus play a major role in flame chemistry and influence flame propagation. Mechanistic understanding of these effects is hampered by very limited thermochemical properties available for relevant organosilane species. This paper presents quantum-chemical calculations and isodesmic reaction schemes for the determination of temperature-dependent heat of formation, entropy, and heat capacity of Si–C–H radicals and molecules, from which group additivity values (GAVs) were obtained from combinatorial considerations. The data for 22 stable Si–C–H species are revised using isodesmic reactions and the related 24 GAVs were refined by considering 19 additional stable Si–C–H species. In addition, quantum chemical calculations are made to calculate the thermochemistry of 61 radicals and used to derive 56 GAVs for Si–C–H containing radicals for the first time. [ABSTRACT FROM AUTHOR]

Machine learning techniques are increasingly being employed to predict molecular properties. Such models are often trained on large computationally derived datasets, and are only as accurate as the underlying data. We exploit the well-known error cancelling effect of isodesmic and homodesmotic reactions to develop a multi-fidelity data-driven molecular property prediction method. First, we propose an optimization-based scheme to quickly and automatically identify all isofragmented reactions for a target molecule u , i.e., balanced reactions involving u and one or more molecules from a given set of molecules (M), which conserve a predefined set of fragments of arbitrary size. Second, we show that such isofragmented reactions can be leveraged to improve the predictive accuracy of a data-driven model by infusing a small high-accuracy dataset comprising molecules in M. We applied this method with a high-accuracy subset of the NIST thermochemistry database and a simple additive data-driven model trained on a QM9 subset. Our results show that the heats of formation using our method were ∼4.4 kcal/mol more accurate on average than the data-driven model. • An optimization-based method for generalized isofragmented reactions. • Error canceling nature of isofragmented reactions used for multifidelity models. • Method to incorporate isofragmented reactions to correct data-driven models. • A data-driven model for heats of formation improved by 4 kcal/mol. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) has been applied to understand the influence of various linkages on the energetic properties and stability of the polynitro-biphenyl compounds. Structures were optimized using the B3PW91/6-31G(d,p) level, and the heats of formation (HOFs) were computed by employing the selected isodesmic reactions. The results reveal that the –N=N– linkage helps to gain high HOF while the –O–, –NH–C(O)NH–, and –NH–C(O)–C(O)–NH– show a negative impact on energy content. Kamlet-Jacobs (K-J) equations were used to determine detonation properties based on the computed densities and HOFs, while stability and sensitivity were investigated by correlating with the bond dissociation energy (BDE), charge on the nitro group, and the balance parameter on surface potentials. Comparing the effect of different linkages on performance and stability of selected polynitro-biphenyl derivatives reveals that –NH–NH– and –N=N– are suitable for a connection between energetic moieties and these results are expected to demonstrate primary information for designing new energetic materials. [ABSTRACT FROM AUTHOR]

The NiI salt [Ni(cod)2]+[Al(ORF)4]– {RF = C(CF3)3} is the starting material for ligand exchange reactions with arenes (benzene, mesitylene and hexamethylbenzene) yielding cationic and purely organometallic 19 valence electron [Ni(cod)(arene)]+ complex salts. The reactions are accompanied by fast solution color changes from yellow to intensely green. Single crystal X‐ray structure analysis, EPR, UV/Vis and IR‐spectroscopic investigations confirm the formation of [Ni(cod)(C6Me6)][Al(ORF)4] (2) as well as [Ni(cod)(mes)][Al(ORF)4] (3, mes = mesitylene) with η6‐coordinated arenes and bidentate cod ligands. The reaction with benzene is plausible but remains less characterized. The energetics of these reactions were used to evaluate diverse DFT methods. 16 functionals with and without D3(BJ) dispersion correction failed to describe the reaction energetics correctly. However, correcting the basic reaction energies with a CCSD(T)/TZ→QZ approach and using further isodesmic reactions with inclusion of COSMO‐RS solvation gave reaction energetics in best agreement with all experimental observations. [ABSTRACT FROM AUTHOR]

Highlights • There were pure samples dicyclopropyldinitromethane and tricyclopropylmethane. • Energy of combustion of these compounds was determined by calorimetry of combustion. • The enthalpies of vaporization were estimated using electrostatic potential model. • The formation enthalpies of liquid and gas of these compounds were calculated. • Obtained experimental and calculation values of formation enthalpy were compared. Abstract The energies of combustion of liquid dicyclopropyldinitromethane and liquid tricyclopropylmethane were determined by calorimetry of combustion at T = 298.15 K. The enthalpies of vaporization were estimated on the basis of electrostatic potential model. The formation enthalpies of the compounds in liquid and gas states were obtained from these data. The gas enthalpies of formation were also calculated by methods of the group additivity and isodesmic reactions. The obtained experimental and calculation values were compared. [ABSTRACT FROM AUTHOR]

Gas-phase enthalpies of formation of diamantane and some of its derivatives were calculated from isodesmic reactions using adamantane as reference species. The G4 theory was applied to calculate the energies of all molecules involved in the isodesmic reactions. The sublimation enthalpies were predicted by the molecular electrostatic potential (MEP) model. Their values were computed from an equation that describes the relationship between the sublimation enthalpy and computed crystal density, and molecular surface area plus four quantities obtained from the surface electrostatic potential. The coefficients in this equation were determined earlier from least squares fitting to reliable values of sublimation enthalpy of 23 adamantanes. The enthalpy formation of diamantanes in the crystalline phase was estimated on the basis of calculated gas-phase enthalpies of formation and sublimation enthalpies. The difference between experimental and theoretical data and inconsistencies in available experimental data are discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Thermochemical network of isodesmic reactions is applied to urea and its derivatives. • 8 ureas are recommended as reference species. • Experimental enthalpies of formation for 9 ureas require reexamination. Abstract The thermochemical network of 91 isodesmic and other balanced reactions was used to adjust simultaneously the enthalpies of formation of 14 urea compounds. The experimental enthalpies of formation of these compounds were treated as unknowns in the least-squares minimization of deviations between the theoretically predicted enthalpies of reaction and experimental values. A result of a least-squares fit confirms the accuracy of experimental enthalpies of formation of 8 ureas, whereas the experimental measurements for 6 urea compounds require re-examination. The gas-phase standard enthalpies of formation of 8 ureas were used as a consistent basis to obtain values for other 15 ureas through isodesmic reactions. To estimate the enthalpies of formation in crystalline state, the sublimation enthalpies were predicted using the molecular electrostatic potential model. [ABSTRACT FROM AUTHOR]

Abstract Some energetic compounds are formed by linking several energetic aromatic rings directly or through bridging groups or spiro or fused structures. To describe the interactions between these aromatic rings, large π-π separation energy was proposed, and a computational approach based on isodesmic reaction equations was also developed. This novel energy can indicate the stability of these energetic compounds, and it is closely related to their sensitivities. The large π-π separation energy was derived for energetic compounds, it can be applied to other directly linked, atom-bridged (or group-bridged), spiro and fused aromatic structures, including some dimetallic coordination compounds. [ABSTRACT FROM AUTHOR]

The simplest ideas of antiaromaticity refer to regular monocyclic systems and the eigenfunctions of the Hückel Hamiltonian for 4n electrons in such systems. The antiaromaticity is expressed in the energy penalty for such idealized systems relative to the Hückel energy for 2n noninteracting π pairs. Observed systems seldom achieve the regular planar geometry assumed in this picture, owing to their ability to ease the antiaromaticity penalty by departures from the regular geometry and also by export of the 4n π electrons' charge to substituents. In this report we estimate numerical values for the stabilization derived from such departures from the structure and the charge distribution of the idealized antiaromatic cyclopropenyl anion for a specific case, 3-dehydro-3-methyl carboxylate cyclopropenyl anion 1(-) using the thermochemical scheme CBSQB3 supplemented by CCSD(T) calculations. According to the isodesmic reaction, the anion 1(-) is destabilized by about 10-15 kcal/mol relative to the saturated 3-dehydro-3-methylcarboxylate cyclopropyl anion 2(-). We propose that the anion relieves a portion of the antiaromatic destabilization by (a) pyramidalization of one carbon of the ring, and (b) export of negative charge into the ester substituent. Both of these responses are expressed in the equilibrium structure of the anion. In the course of the study we estimate the acidity of several related anions and the enthalpy of formation of their neutral conjugate acids, and describe the interconversion of 1 to the dehydrotriafulvalene anion 3(-) by reaction with CO2. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We determined the enthalpy of formation Δ f H m o (g) of gallic acid. • Isodesmic-reactions methodology allowed us to estimate the plausible Δ f H m o (g) of ellagic acid. • DFT/M05-2X and composite ab initio Gn (n = 3, 4) theories provided the consistency of the experimental results. Abstract We report a study on the energetics and structural properties of gallic (1) and ellagic (2) acids. The experimental values of standard enthalpy of formation in solid state at 298.15 K, Δ f H m 0 (cd) of 1 as (−985.0 ± 2.9 kJ·mol−1) and 2 as (−1377.9 ± 4.7 kJ·mol−1) have been determined. The vapour pressure of 1 have been measure by Knudsen effusion methodology and the derived enthalpy of sublimation, Δ cd g H m 0 , was combined with the Δ f H m 0 (cd) in order to derive its gas-phase enthalpy of formation, Δ f H m 0 (1 ,g) = −835.7 ± 4.0 kJ·mol−1. Quantum chemical calculations, at DFT (M05-2X) and composite ab initio Gn (n = 3, 4) levels of theory, provided the consistency of the experimental results and a plausible estimation of Δ f H m 0 (g) of 2 as (−1128.6 ± 6.4 kJ·mol−1), which was deduced from the isodesmic-reactions methodology. [ABSTRACT FROM AUTHOR]

Based on our studies on biphasic self‐assembly behavior of an amphiphilic BF2‐azadipyrromethene (aza‐BODIPY) dye 1, a new analytical model to quantitatively describe the thermodynamic properties of the aggregation involving two competing supramolecular polymerization processes is proposed. In this model, the formation of the metastable as well as the thermodynamically stable aggregates was considered to follow a nucleated polymerization mechanism. The numerical calculation based on the new model gives insight into the formation of different species in such complicate aggregate systems. Moreover, the aggregation of the biphasic self‐assembly processes for dye 1 was investigated by concentration‐dependent UV/Vis spectroscopy. The experimental data were analyzed by using the new model to evaluate the thermodynamic parameters including aggregation constants, the size of nuclei, and the cooperativity the two types of aggregates. Modelling polymerization: A new analytical model of coupled cooperative supramolecular polymerizations is proposed to describe the biphasic aggregation of an amphiphilic BF2‐azadipyrromethene (BODIPY) dye. [ABSTRACT FROM AUTHOR]

The thermochemical network of 300 isodesmic reactions was used to simultaneously adjust the enthalpies of formation for 25 adamantanes. The experimental enthalpies of formation of these compounds were treated as unknowns in the least-squares minimization of deviations between the theoretically predicted enthalpies of reaction and experimental values. The theoretical enthalpies of reactions were obtained using Gaussian-4 (G4) method. A result of a least-squares fit confirms the accuracy of experimental enthalpies of formation of 15 adamantanes, whereas the experimental measurements for 10 adamantanes require re-examination. [ABSTRACT FROM AUTHOR]

We constructed five novel cyclotetramethylene tetranitramine (HMX) derivatives based on the skeleton of HMX ring. The molecules were fully optimized at the B3LYP/6-311G (d) level. We designed isodesmic reactions to calculate their enthalpies of formation. Then, their heats of detonation, detonation velocities, and detonation pressures were calculated using the Kamlet-Jacobs equations on the theoretical densities and enthalpies of formation. Their oxygen balances were computed to estimate whether the title compounds are oxygen-enriched or oxygen-poor. Finally, their impact sensitivity values were evaluated via a simple equation reported in previous studies. In terms of the quantitative standard as high energy density compounds (HEDCs), the potential candidates of HEDCs were selected. [ABSTRACT FROM AUTHOR]

The energy of combustion of a pure sample diphenyl oxide in crystal and liquid states at T  = 298.15 K was determined by isoperibolic calorimeter combustion. The enthalpy of fusion, the triple-point temperature and the purity of the sample were estimated by studying the melting process by calorimetric method. The enthalpies of formation in the crystalline, liquid and gaseous states were calculated. All results are compared with the experimental values reported in the literature. The value of gas-phase enthalpy of formation was calculated by G4 method in combination with isodesmic reactions. The results of this calculation are in good agreement with the obtained experimental value. [ABSTRACT FROM AUTHOR]

The systematic control over association mechanisms of self-assembled materials has been demonstrated through the rational design and synthesis of a series of amphiphilic dinuclear alkynylplatinum(II) bzimpy (bzimpy = 2,6-bis(N-alkylbenzimidazol-2′-yl)pyridine) complexes containing the shape-persistent oligo(p-phenyleneethynylene)s. Multistage morphological transformations from plates to fibers and to spherical nanostructures under different solvent compositions have been demonstrated. The subtle balances between multiple noncovalent interactions including Pt···Pt, hydrophobic, hydrophilic, and π-π stacking interactions are found to have profound impact on the supramolecular assembly of the system, in which a change in the association mechanism from isodesmic to cooperative and back to isodesmic growth has been observed upon increasing hydrophilicity of the complexes. [ABSTRACT FROM AUTHOR]

We have studied prop-2-en-1-imine (1), prop-2-enal (2), ethane-1,2-diimine (3), ethanedial (4), and 2-iminoacetaldehyde (5) to investigate the influence of the negative hyperconjugation in π-π* interaction with the substitution of =CH2 by =NH and/or =O in trans-buta-1,3-diene (6). The analyzes of the π-π* interaction performed from evaluation of the π molecular orbital diagrams and electron localization function method demonstrated, that compared to 6, the substituted compounds 1-5 presented lower electron conjugation, especially in the structures bearing =O. The geometric parameters, natural bond orders, and topological analysis realized by quantum theory of atoms in molecules method indicated a predominant C-C and C=C character for the simple and double C-C bonds in the substituted compounds, 1-5, as compared to 6. Compound 4 had the highest enthalpy of formation, which reflected the lowest π-π* interaction, maintained by the two =O conjugated groups. The natural bond orbital (NBO) and natural resonance theory (NRT) methods revealed that the π-π* electron delocalization in substituted compounds, 1-5, is lower than in 6 from, firstly, of the less favorable interactions: π(X=C) ➔ π*(C=C) and π(X=C) ➔ π*(C=X), despite of the larger π(C=C) ➔ π*(C=X) conjugation, with X = N and/or O, of 1-5 than π(C=C) ➔ π*(C=C) of 6. But, most importantly, the weight of the interaction: nπ(O) ➔ σ*(C-C), was determined from NBO and NRT methods as proportional to the π-π* conjugation and thus demonstrating be decisive to establish the level of π electronic delocalization. [ABSTRACT FROM AUTHOR]

The isodesmic reaction method is applied to calculate the potential energy surface (PES) along the reaction coordinates and the rate constants of the barrierless reactions for unimolecular dissociation reactions of alkanes to form two alkyl radicals and their reverse recombination reactions. The reaction class is divided into 10 subclasses depending upon the type of carbon atoms in the reaction centers. A correction scheme based on isodesmic reaction theory is proposed to correct the PESs at UB3LYP/6-31+G(d,p) level. To validate the accuracy of this scheme, a comparison of the PESs at B3LYP level and the corrected PESs with the PESs at CASPT2/aug-cc-pVTZ level is performed for 13 representative reactions, and it is found that the deviations of the PESs at B3LYP level are up to 35.18 kcal/mol and are reduced to within 2 kcal/mol after correction, indicating that the PESs for barrierless reactions in a subclass can be calculated meaningfully accurately at a low level of ab initio method using our correction scheme. High-pressure limit rate constants and pressure dependent rate constants of these reactions are calculated based on their corrected PESs and the results show the pressure dependence of the rate constants cannot be ignored, especially at high temperatures. Furthermore, the impact of molecular size on the pressure-dependent rate constants of decomposition reactions of alkanes and their reverse reactions has been studied. The present work provides an effective method to generate meaningfully accurate PESs for large molecular system. [ABSTRACT FROM AUTHOR]

The gas-phase enthalpies of formation of four molecules with high flexibility, which leads to the existence of a large number of low-energy conformers, were calculated with the G4 method to see whether the lowest energy conformer is sufficient to achieve high accuracy in the computed values. The calculated values were in good agreement with the experiment, whereas adding the correction for conformer distribution makes the agreement worse. The reason for this effect is a large anharmonicity of low-frequency torsional motions, which is ignored in the calculation of ZPVE and thermal enthalpy. It was shown that the approximate correction for anharmonicity estimated using a free rotor model is of very similar magnitude compared with the conformer correction but has the opposite sign, and thus almost fully compensates for it. Therefore, the common practice of adding only the conformer correction is not without problems. [ABSTRACT FROM AUTHOR]

The supramolecular polymerization of [5]helicenes 1 and 2 is investigated. The self-assembly of these helicenes proceeds by the operation of H-bonding interactions with a negligible participation of π-stacking. The enantiopurity of the sample has a dramatic effect on the supramolecular polymerization mechanism since it reverts the isodesmic mechanism for the racemic mixture to a cooperative one for the enantioenriched sample. Noticeably, the formation of supramolecular polymers efficiently increases the configurational stability of 1,14-unsubstituted [5]helicenes. [ABSTRACT FROM AUTHOR]