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Tubulin self-association is a critical process in microtubule dynamics. The early intermediate structures, energetics, and their regulation by fluxes of chemical energy, associated with guanosine triphosphate (GTP) hydrolysis, are poorly understood. We reconstituted an in vitro minimal model system, mimicking the key elements of the nontemplated tubulin assembly. To resolve the distribution of GTP- and guanosine diphosphate (GDP)-tubulin structures, at low temperatures (∼10 °C) and below the critical concentration for the microtubule assembly, we analyzed in-line size-exclusion chromatography-small-angle X-ray scattering (SEC-SAXS) chromatograms of GTP- and GDP-tubulin solutions. Both solutions rapidly attained steady state. The SEC-SAXS data were consistent with an isodesmic thermodynamic model of longitudinal tubulin self-association into 1D oligomers, terminated by the formation of tubulin single rings. The analysis showed that free dimers coexisted with tetramers and hexamers. Tubulin monomers and lateral association between dimers were not detected. The dimer-dimer longitudinal self-association standard Helmholtz free energies were -14.2 ± 0.4 kBT (-8.0 ± 0.2 kcal mol-1) and -13.1 ± 0.5 kBT (-7.4 ± 0.3 kcal mol-1) for GDP- and GTP-tubulin, respectively. We then determined the mass fractions of dimers, tetramers, and hexamers as a function of the total tubulin concentration. A small fraction of stable tubulin single rings, with a radius of 19.2 ± 0.2 nm, was detected in the GDP-tubulin solution. In the GTP-tubulin solution, this fraction was significantly lower. Cryo-TEM images and SEC-multiangle light-scattering analysis corroborated these findings. Our analyses provide an accurate structure-stability description of cold tubulin solutions.

Enhanced thermodynamic stability is a fundamental characteristic of aromatic molecules, yet most previous studies of aromatic stabilization energy (ASE) have been limited to small rings with up to 18 π-electrons. Here we demonstrate that ASE can be detected experimentally in π-conjugated porphyrin nanorings with Hückel circuits of 76-108 π-electrons. This conclusion is supported by analyzing redox potentials to calculate the energy change for isodesmic reactions that convert an aromatic ring to an antiaromatic ring or vice versa. It is also supported by analyzing the energy barriers to conformational equilibria that disrupt aromaticity in the transition state. Both types of experiment indicate that cationic porphyrin nanorings display ASEs of 1-5 kJ mol-1. Density functional theory calculations reproduce the results for both types of experiment and predict ASEs in the range of 1-16 kJ mol-1. The experimental ASEs in porphyrin nanorings are compared with an experimental ASE of [18]annulene of ∼11 kJ mol-1, deduced from analysis of the energy barriers to conformational equilibria in [16], [18], and [20]annulene. Calculated energies of isodesmic reactions give an ASE of ∼37 kJ mol-1 in [18]annulene. This work contributes to a fundamental understanding of aromaticity in large macrocycles.

Controlled supramolecular polymerization has emerged as an active research area in the last decade. Recent contributions have revealed that their dynamic self-assembly into different molecular packings is strongly influenced by kinetic effects. However, the examples reported are very limited and the understanding of pathway complexity by molecular design remains elusive. In this work, two supramolecular monomers 1 and 2 by coupling BODIPY with a class of newly designed pyrazole-based motifs were designed. The flexible ethylene linker together with the presence of benzamide groups bring about intramolecular hydrogen-bonding (H-bonding) interactions between pyrazole N as the H-bonding acceptor and the adjacent amide. Our results unveiled two distinct pathways during self-assembly. Namely, a metastable J-aggregate is formed through an isodesmic model, while the thermodynamically stable H-aggregate obeys the cooperative mechanism. The detailed transformation of 1J-agg into 1H-agg, as well as the individual formation mechanisms of 1J-agg and 1H-agg have been investigated by various spectroscopic techniques. Encouraged by the drastic emission changes of monomers and aggregates, luminescence temperature sensing has been demonstrated as a proof of concept.

A prerequisite for the generation of detailed fundamental kinetic models is the availability of accurate thermodynamic properties. To address the scarcity of accurate experimental data, theoretical calculations can be used. The accuracy of these quantum chemistry methods for determination of thermodynamic properties can be improved by making use of empirical correction methods, such as the isodesmic bond additivity correction (BAC) method. In this work, ab initio calculations for a set of 371 molecules have been performed to determine a new set of BACs for the CBS-QB3 level of theory. For each of these molecules also accurate experimental data, that is with an experimental uncertainty less than 3 kJ mol(-1), is available. This broad dataset of hydrocarbons and heteroatomic compounds contains (non)cyclic molecules with a wide range of functional groups consisting of hydrogen, carbon, oxygen, nitrogen, and sulfur. The new set of 26 BAC parameters is obtained via linear regression analysis, minimizing the differences between experimental and corrected CBS-QB3 values. The CBS-QB3 method combined with BACs succeeds in approximating the experimental standard enthalpy of formation at 298 K with an accuracy of 4 kJ mol(-1) for almost all species. The BACs reduce the mean absolute deviation for the complete dataset from 5.65 to 2.37 kJ mol(-1), corresponding to a decrease of the root mean square deviation from 6.95 to 3.00 kJ mol(-1).

The utilization of anions to induce the formation of self-assembled supramolecular polymers in solution is an undeveloped area of host-guest chemistry. We report in this manuscript a comparative study of two tripodal anion receptors by hydrogen or halogen bonding interactions to form self-assembled supramolecular structures induced by the presence of anions. DOSY NMR and DLS experiments provided evidence for the formation of supramolecular structures in solution in both halogen and hydrogen bond donors with H2PO4- anions. The nucleation and elongation constants obtained using the thermodynamic model indicate that the polymers grow following an isodesmic mechanism. Emission studies demonstrate that only the formation of the supramolecular polymer between the halogen bond donor receptor and H2PO4- anions results in the appearance of the excimer emission band.

International audience; The synthesis of two series of N-annulated perylene bisimides (PBIs), compounds 1 and 2, is reported, and their self-assembling features are thoroughly investigated by a complete set of spectroscopic measurements and theoretical calculations. The study corroborates the enormous influence that the distance between the PBI core and the peripheral groups exerts on the chiroptical properties and the supramolecular polymerization mechanism. Compounds 1, with the peripheral groups separated from the central PBI core by two methylenes and an ester group, form J-type supramolecular polymers in a cooperative manner but exhibit negligible chiroptical properties. The lack of clear helicity, due to the staircase arrangement of the self-assembling units in the aggregate, justifies these features. In contrast, attaching the peripheral groups directly to the N-annulated PBI core drastically changes the self-assembling properties of compounds 2, which form H-type aggregates following an isodesmic mechanism. These H-type aggregates show a strong aggregation-caused quenching (ACQ) effect that leads to nonemissive aggregates. Chiral (S)-2 and (R)-2 experience an efficient transfer of asymmetry to afford P- and M-type aggregates, respectively, although no amplification of asymmetry is achieved in majority rules or "sergeants-and-soldiers" experiments. A solvent-controlled stereomutation is observed for chiral (S)-2 and (R)-2, which form helical supramolecular polymers of different handedness depending on the solvent (methylcyclohexane or toluene). The stereomutation is accounted for by considering the two possible conformations of the terminal phenyl groups, eclipsed or staggered, which lead to linear or helical self-assemblies, respectively, with different relative stabilities depending on the solvent.

Two ionic and two neutral luminescent platinum(II) isocyanide complexes bearing different linkers (amide vs. ester) 1–4 have been rationally designed and synthesized. Their supramolecular polymerization and gelation properties have been comprehensively investigated by spectroscopic studies. Significant emission enhancement was observed upon aggregation, with their emission maxima highly dependent on pincer ligands. Due to the additional ionic interaction, two ionic complexes 1–2 provide stronger driving forces for the supramolecular polymerization than the neutral derivatives 3–4. Moreover, different linkers (amide vs. ester) were found to lead to distinct supramolecular polymerization mechanisms. Amide-bearing complex 1 undergoes highly cooperative supramolecular polymerization, while replacement of the amide by ester groups leads to isodesmic self-assembly. Unexpectedly, only ester-containing derivative 2 can form reversible metallogel. The reason is attributed to its synergistic participation of π–π and ionic interactions, as well as suitable organization of anions. This work presented here highlights that subtle variation of noncovalent interactions, particularly hydrogen bonding and ionic interactions, exerts pronounced influence on the supramolecular self-assembly mechanism and gel formation.

The use of stoichiometric organoborane reductants in organic synthesis is well established. Here these reagents have been rendered catalytic through an isodesmic B-O/B-H transborylation applied in the borane-catalyzed, chemoselective alkene reduction and formal hydrofunctionalization of enones. The reaction was found to proceed by a 1,4-hydroboration of the enone and B-O/B-H transborylation with HBpin, enabling catalyst turnover. Single-turnover and isotopic labeling experiments supported the proposed mechanism of catalysis with 1,4-hydroboration and B-O/B-H transborylation as key steps.

There is considerable interest in dynamic materials featuring modular components with nano-scale dimensions and controlled responsiveness to external stimuli. Supramolecular polymers are a class of materials that fulfil all these conditions well. Here, we present a family of host–guest supramolecular polymers that combine the outstanding complexing properties of tetraphosphonate cavitands toward N-methylpyridinium guests with molecular switching. The designed monomer is a cavitand featuring four inward facing PO groups at the upper rim and a single N-methylpyridinium unit at the lower rim, forming instantaneously a polymeric species in solution, thanks to the high complexation constants measured for these host–guest interactions. This system has been analyzed by NMR spectroscopy and electrochemical techniques. In order to interpret the results of diffusion-sensitive experiments, we took advantage of the X-ray crystal structure obtained for the polymeric species and developed an original treatment for the PGSE data by non-linear fitting. The analysis of the experimental data identified an isodesmic polymerization model at a monomer concentration below 20 mM, driven by intrachain host–guest interactions, and an additional level of tetrameric bundle aggregation above 20 mM, due to interchain dipolar and quadrupolar interactions. Two orthogonal disassembly procedures have been implemented: electrochemical reduction for the linear chains and solvent-driven dissolution for the bundles.

Various rhodium(I) pincer complexes with different structural features have been prepared and found to display interesting self-assembly properties due to the extensive Rh(I)···Rh(I) interactions. The incorporation of electron-withdrawing −CF3 substituent has been found to improve the stability of the complexes and also facilitate the directed assembly of complex molecules, providing an opportunity for the systematic investigation of the various noncovalent interactions in their versatile self-assembly behaviors and insights into the structure–property relationship in governing the intermolecular interactions. An isodesmic growth mechanism is identified for the solvent-induced aggregation process. The complex molecules exhibit intense low-energy absorption bands corresponding to the absorptions of the dimers, trimers, and higher order oligomers upon aggregation, with energies related to the electronic properties of the tridentate N-donor ligand. Chiral auxiliaries have also been introduced into the rhodiu...

Pathway complexity in supramolecular polymerization has recently sparked interest as a method to generate complex material behavior. The response of these systems relies on the existence of a metastable, kinetically trapped state. In this work, we show that strong switch-like behavior in supramolecular polymers can also be achieved through the introduction of competing aggregation pathways. This behavior is illustrated with the supramolecular polymerization of a porphyrin-based monomer at various concentrations, solvent compositions, and temperatures. It is found that the monomers aggregate via an isodesmic mechanism in weakly coupled J-type aggregates at intermediate solvent quality and temperature, followed by nucleated H-aggregates at lower solvent qualities and temperatures. At further increased thermodynamic driving forces, such as high concentration and low temperature, the H-aggregates can form hierarchical superhelices. Our mathematical models show that, contrary to a single-pathway polymerization, the existence of the isodesmic aggregation pathway buffers the free monomer pool and renders the nucleation of the H-aggregates insensitive to concentration changes in the limit of high concentrations. We also show that, at a given temperature or solvent quality, the thermodynamically stable aggregate morphology can be selected by controlling the remaining free external parameter. As a result, the judicious application of pathway complexity allows us to synthesize a diverse set of materials from only a single monomer. We envision that the engineering of competing pathways can increase the robustness in a wide variety of supramolecular polymer materials and lead to increasingly versatile applications.

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.

Density functional theory (DFT) has been applied to explore the general rules for structure design of azo compounds through energetic properties and stability. Structures of 2,2′, 4,4′, 6,6′- hexanitroazobenzene (HNAB) derivatives were designed and optimized using B3LYP /6-31G(d,p) level, and the heat of formation (ΔfH) were evaluated by constructing isodesmic reactions. Results reveal that the azo bridging (–N N–) is useful for increasing the heat of formation. Kamlet–Jacobs equations were employed to evaluate detonation performance, while the sensitivity was explored by correlating with the bond dissociation energy (BDE), electronic structural parameters (EHOMO, ELUMO, and ΔELUMO-HOMO), oxygen balance (OB), and charges on nitro group (QNO2). According to our calculations, some designed HNAB derivatives possess interesting properties, such as good detonation performance and high stability, even beyond RDX and HMX, revealing that the presence of azo bridging (–N N–) backbone together with the introduction of various energetic groups is a promising choice in the design of high energy density materials (HEDMs).

In the present work, the thermochemical properties of seventeen adducts, expected for the reaction of NH2CO with HCO, are studied using the CBS-Q energies of the isodesmic/isodesmotic and the atomization reactions as well as the group additivity method. The good agreement between the values of ΔfHo298.15, calculated using the different methods and the quantum mechanical approaches are observed. According to the values of ΔfHo298.15, calculated in the present work, the formation of trans- and cis-diones (trans- and cis-1NH2(O)C C(O)H) is thermochemically more favorable than the formation of carbene esters (1NH2C(O) O CH and 1NH2C OC(O)H). Nevertheless, in all those cases, the reactions of formation of these adducts in the ground singlet state are exothermic. The formation of adducts in the triplet state is favorable only in the case of the trans- and cis-diones (trans- and cis-3NH2(O)C C(O)H). The formation of peroxides (NH2C O O CH) as products of this reaction is found to be impossible for both the singlet and triplet states. The mean values of ΔfHo298.15(trans-1NH2(O)C C(O)H)iso = −293.6 ± 4.3 kJ/mol and ΔfHo298.15(cis-3NH2(O)C C(O)H)iso = −6.7 ± 3.2 kJ/mol of the most thermochemically favorable adducts, respectively, in the lowest singlet and triplet states have been calculated, respectively, using the CBS-Q enthalpies of seven and three isodesmotic reactions. The first of these two values also agrees well with the values of ΔfHo298.15(trans-1NH2(O)C C(O)H)Benson = −299.5 kJ/mol and ΔfHo298.15(trans-1NH2(O)C C(O)H)atom = −302 kJ/mol, calculated, respectively, using the group additivity method and thermochemistry of the atomization reaction, as well as with tabulated values of ΔfHo298.15 of others trans-diones (H(O)C C(O)H, CH3(O)C C(O)H, CH3(O)C C(O)CH3, HO(O)C C(O)OH, HO(O)C C(O)NH2, NH2(O)C C(O)NH2) and with the energy of dissociation of their (O)C C(O) bond (BDE). The exothermic formation of the (O)C C(O) bond have also been determined for the several trans-diones (H(O)C C(O)H, CH3(O)C C(O)H, CH3(O)C C(O)CH3, HO(O)C C(O)OH) in the lowest triplet state. Moreover, the good linear correlation between the values of BDE((O)C C(O)) and energy of S-T gap of the corresponding trans-diones is observed for all considered trans-diones, excluding only Cl(O)C C(O)Cl. The reactions of the cis-3NH2(O)C C(O)H with the main stable components of the prebiotic atmosphere of Earth, such as CH4 and NH3, are assumed on the basis of their thermochemistry. The values of ΔfHo298.15, calculated in the present work, have also been used for the estimation of the increment values for several groups containing carbene that are not available in the literature. Based on the scan of the potential energy surface, it is concluded that the formation of trans-1NH2(O)C C(O)H is barrierless and the value of rate constant of it formation must be in the range of (3 ± 2) × 10−11 cm3/(molec. s). As a result, this reaction pathway should be one of the main channel for the sink of NH2CO radicals under the atmospheric conditions of the prebiotic Earth, and leads to the formation of relatively stable cis- and trans-1NH2(O)C C(O)H.

The molecular structures and relative energies of various methyl and tert-butyl substituted naphthalenes and azulenes have been studied by DFT method ωB97XD/6-311(d, p) with dispersion correction. The relative energies of molecules and effects of steric repulsion, strain and ring distortion were estimated via the appropriate homodesmotic and isodesmic reactions. The calculated standard reaction enthalpies allowed us to estimate the magnitude of various nonbonding intramolecular interactions. The introduction of bulky tert-butyl substituents leads to significant distortions of naphthalene and azulene rings. The aromaticity of the rings had been estimated using HOMA indices. For the most distorted aromatic rings it was found that the net destabilization is more pronounced in octa-tert-butylnaphthalene than in the octa-tert-butylazulene even though the structural distortions of the rings were smaller in the former.

In the present work, the thermochemical properties of the several N,N′-ethylenbisalkaneamides are calculated using RB3LYP/6-31G(d,p), UB3LYP/6-311++G(d,p), CBS-4M and CBS-Q approaches. The values of standard enthalpies of their formation ((ΔfHo298.15)(g)) are calculated using thermochemistry of the isodesmic reactions as well as using the group additivity methods. Due to the high uncertainty in the values of (ΔfHo298.15)(g) of the high atomic molecules, calculated using different approaches, the simple methodology for determination of (ΔfHo298.15)(g) values of compounds with more than 16 “heavy” atoms (C, N and O) is proposed. This methodology is based on the extrapolation of the linear dependence of results of the CBS-4M and RB3LYP/6-31G(d,p) calculations. Reliability of the values of (ΔfHo298.15)(g), determined using this methodology, is comparable with the results of CBS-4M calculations. The following expression for the determination of (ΔfHo298.15)CBS-4M = 0.45 + 1.023 × (ΔfHo298.15)RB3LYP describes well the values of (ΔfHo298.15)(g) of amides, n-alkanes and N,N′-ethylenbisalkaneamides, calculated using the CBS-4M approach. The values of (ΔfHo298.15)CBS-4M = −578.9 ± 7 and −1128.8 ± 7 kJ/mol, determined using this expression, and the values of (ΔfHo298.15)RB3LYP, calculated, respectively, for (C4H9C(O)NHCH2)2 and (C17H35C(O)NHCH2)2, agree with those values determined using the group additivity method (respectively, equal to −568.8 and −1126.8 kJ/mol). Values of (S°298.15)(g) of the considered N,N′-ethylenbisalkaneamides are also calculated in the present work. It’s shown that tabulated values of (S°298.15)(g) of the n-alkanes and n-alkaneamines depend linearly upon those values, calculated using RB3LYP/6-31G(d,p) quantum mechanics (QM) approach. In both cases, the same values of slope of these dependencies are observed. As a result, the following expression for determination of S°298.15((CnH2n+1C(O)NHCH2)2) = −108.2 + 1.266 × S°298.15(((CnH2n+1C(O)NHCH2)2)RB3LYP) and the method for determination of (S°298.15)(g) values of high atomic compounds that belong to the same homologous series is proposed. The values of S°298.15((CnH2n+1C(O)NHCH2)2), calculated in the present work for considered compounds are: 383.5 (n = 0), 481.4 (n = 1), 554.8 (n = 2), 630 (n = 3), 712.3 (n = 4) и 1709.9 (n = 17) J/(mol K).

This paper assesses the performance of quantum chemical models with regard to the calculation of enthalpy of formation of CHON molecules using isodesmic reactions. The high accuracy of prediction of enthalpy of formation of CHON compounds can be achieved by the combination of isodesmic reaction scheme with composite ab initio methods. The best composite methods, such as G4, G4MP2, CBS-QB3, and CBS-APNO, can attain near chemical accuracy or better depending on reaction type. Other composite methods yield the same accuracy only in conjunction with isodesmic or homodesmotic reactions. The DFT and MP2 methods lead to good results if they are used with homodesmotic reactions. For CHO compounds, all composite methods demonstrate the high accuracy not only with isodesmic and homodesmotic reactions, but also with isogyric reactions. Moreover, the DFT and MP2 methods can also yield a high accuracy estimate of the enthalpy of formation when they are used with isodesmic or homodesmotic reactions. Four composite methods (G4, G3, CBS-APNO, and CBS-QB3) employed in conjunction with 45 isogyric reactions yield the enthalpy of formation of hydrazine (97.7 ± 2.0 kJ/mol) in agreement with the best approximating to CCSD(T)/CBS energy, thus calling into question the usually quoted experimental value of 95.5 kJ/mol.

Structure of six-membered cyclic aminoiminocarbenes (pyrimidine ylidenes) and their group 13–15 homologues was studied by quantum chemical calculations. Isodesmic and dimerization reaction energies, NICS values, frontier molecular orbitals, as well as NBO, Bader’s “atoms in molecules” and Laplacian bond order (LBO) analyses were employed for estimating relative stability of the studied carbenes (carbene homologues). They show a low degree of aromatic delocalization and considerable variation of electronic structure depending on the nature of divalent element. The predicted stability for the series of interest is lower than that for the corresponding five-membered Arduengo carbenic structures, but comparable with Alder’s bis(dimethylamino)carbene.

Salts, when added to milk, profoundly influence casein aggregation.. Even though this well-known phenomenon has been widely exploited, there are still many unanswered questions. How do salts affect casein aggregation? Does water contribute significantly to the aggregation change? The key to answering these questions comes from statistical thermodynamics, i.e., the principles of physics that can link macroscopic data to the collective behaviour of molecules. We present two theoretical approaches, a rigorous approach which demands far more measurements than reported hitherto, and an approximate and pragmatic approach based on stoichiometric models (isodesmic model for aggregation equilibria and von Smoluchowski model for kinetics) that can yield information on protein-water and protein-salt interactions from “real life” experimental measurements on a model systems available in a wide variety of formats. Using the experimental data in the literature, casein aggregation in the absence of κ-casein has been shown to be modulated by protein-salt interaction, while the contribution from water structure changes has been shown to be negligible.

For new high-energy density compounds, a series of new bicyclo[2.2.1]heptane derivatives were designed and studied by density functional theory (DFT) method. The heat of formation (HOF) was evaluated by the isodesmic reaction. The densities and the heats of sublimation were predicted by the electrostatic potential analysis at B3PW91/6-31G(d,p) and B3LYP/6-311++G(2df,2p) levels, respectively. The detonation performances were predicted by the Kamlet-Jacobs equations. The bond dissociation energies (BDE) and impact sensitivity that is evaluated by the free space per molecule were also studied to give a better understanding of the stability. Results show that HOFs increase with the increasing number of N atoms. When the number of NO2 groups is larger than 4, HOFs generally increase with the increasing number of NO2 groups. Even though solid-phase HOF is decreasing, detonation energy is always rising with Oxygen Balance (OB) closing to zero-OB, and positive value of OB will largely reduce detonation energy. Detonation velocity and detonation pressure of the designed compounds are in the range of 5.62–9.46 km/s and 11.72–41.44 GPa, respectively. And detonation velocity and detonation pressure always increase with the increasing number of N atoms or NO2 groups except when OB is positive value. BDEs of all designed compounds are larger than 20 kcal/mol shows that all designed compounds have a reasonable thermal stability. The calculated impact sensitivities show that all designed HEDCs have acceptable sensitivity. Especially impact sensitivity of C7, D7, E7, F6 and G6 are expected to be very close to Tetryl (h50 = 25 cm). Considering the thermal stability, impact sensitivity and detonation performance, A8, B8, C7, C8, D7, E7, F6 and G6 might be interesting candidates for use as HEDCs.

Pyrolysis of azido- meta -meconine yields only a single product 1D, which has been characterized spectroscopically ( 1 H NMR, 13 C NMR, HSQC, DEPT & MS). These results reveal that the fused five-member lactone ring can influence the product selectivity. The DFT calculations suggest the formation of favourable oxazolidine intermediate compared to azirine ( 1Z ) and ketenimine ( 1H ) intermediates. The isodesmic analysis showed that the fused lactone aryl nitrene ( 1N ) would have more strain to form azirine ( 1Z ) intermediate than the corresponding aryl nitrene ( 1M ).

The synthesis of various new polyvalent nitrocarbamates derived from sugar alcohols was accomplished by an economically benign two-step synthesis. The precursor carbamates were synthesized with the reagent chlorosulfonyl isocyanate (CSI) and further nitrated using mixed acid. The starting materials, sugar alcohols, are renewable biomass, mainly used in food and cosmetic industry. The structures of one carbamate and one nitrocarbamate were exemplary described by single-crystal X-ray-analysis. The heat of formation is calculated by the use of isodesmic reactions and the energetic performance data were estimated. All compounds were fully characterized by elemental analysis, vibrational spectroscopy, (1)H, (13)C, and (14/15)N NMR spectroscopy and thermal analysis (DSC). The nitrocarbamates exhibit good detonation performance and have significantly lower sensitivities compared to the commonly used nitrate ester explosive PETN.

We have reached novel borastannylenes with an unprecedented common frame work that can accommodate up to five nitrogen heteroatoms. All species appear as ground state minima on their energy surface, for showing no negative force constant. Singlets 7-boratricyclo[1.1.1.01,7.07,3.07,5]hexa-2-stannylenes (1s-20s) are ground states and more stable than their corresponding triplets (1t-20t). They are compared and contrasted with respect to their geometrical parameters, stability (ΔEs-t), heat of hydrogenation (ΔEH), nucleophilicity (N), electrophilicity (ω), and isodesmic reactions at B3LYP/AUG-cc-pVTZ//B3LYP/6–311++G** level of theory. The highest stability belong to the singlet 1,3-diaza-7-boratricyclo[1.1.1.01,7.07,3.07,5]hexa-2-stannylene (5) which shows the highest value of ΔEs-t. Boracyclics singlet 1,4,6-triaza-7-boratricyclo[1.1.1.01,7.07,3.07,5]hexa-2-stannylene (14s) with coordinate covalent bond between nitrogen and stannylene center and 1,4,5,6-teraaza-7-boratricyclo[1.1.1.01,7.07,3.07,5]hexa-2-stannylene (18s) with high LPN → LP*Sn interactions have low ω. Also, the highest band gap (ΔEHOMO–LUMO) belong to theirs. Our investigation introduces novel stannylene with possible applications in chemistry such as semiconductors, cumulated multi-dentate legends, etc.

A detailed combustion mechanism of hydrocarbon fuels usually contains a large number of reactions and need to have kinetic data assigned to them, where the rate constants are usually given by approximate estimation leading to inaccuracies. In this work, a method for construction transition state (TS) and an isodesmic reactions correction scheme for accurate and automatic calculation of rate constants have been designed. These methods are tested using the cyclization reactions of QOOH radicals and the concerted elimination reactions of RO2 radicals. The results show that the automatic TS construction method is effective to construct the initial guesses of the transition states, the isodesmic reactions corrected results are close to the CCSD(T) results and some of the rate constants are significantly different from the rate constants used in the automated mechanism generator, indicating that it is necessary and significant to perform on-the-fly accurate calculation of rate constants in an automated mechanism generator.

The reaction mechanism of OH-initiated hydrogen abstraction reactions of CF3C(O)OCH2CH3, ethyl trifluoroacetate (ETFA) were investigated by performing DFT calculations. The optimized geometries, frequencies and minimum energy path were obtained at MPWB1K in conjunction with 6-31+G(d,p) basis set. The single-point energy calculations were further refined by using high level G2(MP2) method. Two conformers of ETFA have been located and considered for kinetic calculations. The rate constants of the two reactions are determined for the first time in a wide temperature range of 200–450 K. The evaluated rate constant (2.43 × 10−13) at 298 K is found to be in good agreement with the available experimental data [(2.64 ± 0.59) × 10−13]. The standard enthalpies of formation for species are evaluated by using a series of isodesmic reactions. The OH-driven atmospheric life time are also estimated and compared with literature values. Based on mechanistic and kinetics studies, we suggest that the H abstraction from CH2 group is more favorable than the CH3 group.

Quantum chemical calculations were carried out at the M062X, B3LYP, and CCSD methods in order to examine the relative energies of 2,4,6,1,3,5-trisilatriphosphabenzene (2) and 2,4,6-trisilatriazine (1) compared to their isomer (mono, di and tri)silylenes. The relative energies of isomer silylenes are higher than the parent compound 2,4,6,1,3,5-trisilatriphosphabenzene (2). On the other hand, 2,4,6-trisilatriazine (1) is a higher energy compound than its silylene isomers. Both compounds 1 and 2 are aromatic that is supported by calculated geometries, nucleus-independent chemical shifts (NICS), para-delocalization indices (PDIs), resonance and isodesmic/homodesmic stabilization energies (RSEs and ISEs/HSEs, respectively). Both NICS(1) and PDIs predict that silylene isomers of 2 (except disilylene) are fairly aromatic and (all three) silylene isomers of 1 are marginally aromatic.

The mechanism, kinetics and thermochemistry of the reaction of (CF3)2C(OH)CH3 with OH radicals are theoretically investigated using DFT based M06-2X functional method. Three important H-abstraction channels have been identified for (CF3)2C(OH)CH3 + OH reaction and one transition state has been located for each reaction channel. Formation of pre-reactive complex at the entry of each reaction channel indicates an indirect mechanism for hydrogen-abstraction reaction. The rate coefficients for (CF3)2C(OH)CH3 are evaluated using canonical transition state theory along with Eckart's tunneling correction over a wide range of temperature (270–1000 K). At 298 K, our calculated total rate coefficient for (CF3)2C(OH)CH3 + OH reaction is in good agreement with the experimental result. The results show that H-abstraction from the CH3 group is the predominant channel and has more contribution to the total rate coefficient than that from the OH group of (CF3)2C(OH)CH3. The standard heats of formation for (CF3)2C(OH)CH3 molecule, (CF3)2C(OH)CH2 and (CF3)2C(O)CH3 radicals are estimated by using group-balanced isodesmic reactions and the values are −1599.6, −1369.8 and −1335.6 kJ mol−1, respectively at 298 K. The atmospheric lifetime of (CF3)2C(OH)CH3 is estimated to be around 5.0 years. The 100-year time horizon global warming potentials of (CF3)2C(OH)CH3 with respect to CO2 is 705. Potential atmospheric degradation routes for the resulting (CF3)2C(OH)CH2 radical is also discussed here.

We present a detailed study of the molecular conformations, vibrational spectra and thermochemistry of the CF2(OH)CF2OONO2 and CF3CF2OONO2 peroxynitrates. In addition, we studied the CF2(OH)CF2OO, CF2(OH)CF2O, CF3CF2OO and CF3CF2O radicals, formed by the rupture of Osingle bondN and Osingle bondO bonds of the above peroxynitrates. The geometric structures of the most stable conformations were determined by density functional theory calculations. At the B3LYP/6-311++G(3df,3pd) level of theory, both peroxynitrates present dihedral angle COON values of about 104°. At the best levels of theory employed, G3(MP2)B3 and G4(MP2), the standard enthalpies of formation at 298 K derived from isodesmic reactions, are −265.6, −248.6 and −248.5 kcal mol−1 for CF2(OH)CF2OONO2, CF2(OH)CF2OO and CF2(OH)CF2O respectively; while for CF3CF2OONO2, CF3CF2OO and CF3CF2O the values of −268.2, −252.6 and −251.9 kcal mol−1 were obtained. Bond dissociation enthalpies of 25.1 and 35.0 kcal mol−1 have been predicted for the first time for CF2(OH)CF2OOsingle bondNO2 and CF2(OH)CF2Osingle bondONO2 and of 23.7 and 34.2 kcal mol−1 have been estimated for CF3CF2OOsingle bondNO2 and CF3CF2Osingle bondONO2. The obtained result of the dissociation enthalpy of CF3CF2OOsingle bondNO2 is in excellent agreement with the available experimental determination. Therefore, the Osingle bondN bond fission is the primary thermal dissociation pathway for both studied peroxynitrates. Fil: Delvalle Mongelós, Rosa Isabel. Universidad Nacional de Asuncion; Paraguay Fil: Badenes, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de la Plata; Argentina

The molecular structures of azole substituted tetrazolo[1,5-b][1,2,4,5]tetrazine (AsTT) derivatives were designed and fully optimized at the B3PW91/6-31G(d,p) level of theory. Isodesmic reaction was constructed to predict gas phase heat of formation (HOF) and heat of sublimation derived from Politzer approach was used to calculate HOF at condensed phase. The presence of nitrogen-rich AsTT backbone is found promising in increasing the HOF values. Politzer approach also extended to predict the densities of these derivatives from the calculated surface electrostatic properties. Kamlet–Jacobs equations were used to calculate detonation performances based on predicted solid phase heats of formation, densities and gaseous detonation products. The charge distribution on molecular surface and free space per molecule in the unit cell were used to analyze the sensitivity. The explosive power and power index were calculated to assess the potential of designed compounds. According to our calculations, the designed AsTT derivatives possess interesting explosive properties and could be the potential addition in high energy materials (HEMs).

The major reaction path for oxidation of di-tert-butyl peroxide (DTBP) is generally considered to occur via fission of the weak peroxide ROOR bond at temperatures above 393 K. The initial stable intermediates in the thermal decomposition or combustion of DTBP are acetone and ethane, and the overall reaction is accompanied by an important heat release which when mixed with air (oxygen) may exceed the self-ignition temperatures. A kinetic study on plausible DTBP reaction paths was initiated in this work, and a detailed study of the thermochemistry of new intermediates, transition state structures, and products is reported. The density functional theory (DFT; B3LYP/6-311g(d,p)), which is practical for large compounds along with the composite ab initio G3MP2B3 and G3 calculations, (when possible), are used. Computational chemistry results from DFT and ab initio calculations are coupled with isodesmic reaction analysis which, as demonstrated in previous studies, results in good accuracy. Over 10 unimolecular decomposition pathways are identified and reported.

The effect of the SF5 group as a substituent on various classes of carbocation was probed computationally employing DFT to examine geometrical changes, relative energies, and charge delocalization modes. Relative electron withdrawing power of the SF5 group was compared with CF3, NO2, CN, and SCF3 through isodesmic reactions. NPA charge densities were employed to gauge the influence of SF5 group on the charge delocalization modes in the carbocations. Fil: Borosky, Gabriela Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Laali, Kenneth K.. University of North Florida; Estados Unidos

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF3CHFCF2OCF3 with OH radicals and Cl atoms using M06-2X/6-31+G(d,p) level of theory. The energetic calculations were refined by using aug-cc-pVTZ basis set. Our calculations reveal that OH-initiated hydrogen abstraction is thermodynamically and kinetically more facile than that from the Cl-initiated hydrogen abstraction. Using group-balanced isodesmic reactions, the standard enthalpies of formation (ΔHf°) for species and bond dissociation energies for C H bond are also reported. The ΔHf° for CF3CHFCF2OCF3 and •CF(CF3)CF2OCF3 species calculated from M06-2X/6-31+G(d,p) results are −523.15 and −471.65 kcal mol−1, respectively. The rate constants evaluated by canonical transition state theory (CTST) are found to be 1.22 × 10−15 and 3.40 × 10−17 cm3 molecule−1 s−1 which are in a reasonable agreement with the available experimental data of (1.43 ± 0.28) × 10−15 and (4.09 ± 0.42) × 10−17 cm3 molecule−1 s−1, respectively, for OH and Cl-initiated hydrogen abstraction reactions. The atmospheric life time of CF3CHFCF2OCF3 is estimated to be 38.5 years. The atmospheric fate of the alkoxy radical, CF3CF(O•)CF2OCF3 is also investigated for the first time using same level of theory.

PhSF5 1 reacts with NO2+BF4−/TfOH in CH2Cl2 (DCM) at room temperature to give 1-nitro-3-(pentafluorosulfanyl)benzene 2 in near quantitative yield. The dinitro derivative 4 is synthesized from 2 by reaction with NO2+BF4−/TfOH at 70 °C. The p-MeC6H4SF5 is mononitrated at room temperature with NO2+BF4−/DCM and dinitrated with NO2+BF4−/TfOH. Substrate selectivity ( k PhSF 5 / k RPh ) in competitive nitration for PhSF5/PhCF3 and PhSF5/PhNO2 with NO2+BF4− in DCM at room temperature was determined at 21.3 and ∼1 respectively. Relative stability of the corresponding benzenium ions were gauged by DFT from the isodesmic proton transfer reaction SF5–C6H6+ + R-C6H5 → SF5–C6H5 + R-C6H6+ (R = CF3 and NO2). These studies indicate that reactivity of ArSF5 in SEAr is similar to ArNO2.

Bending at the valence angle N–C α –C′ ( τ ) is a known control feature for attenuating the stability of the rare intramolecular i → i hydrogen bonded pseudo five-membered ring C 5 structures, the so called 2.0 5 helices, at Aib. The competitive 3 10 -helical structures still predominate over the C 5 structures at Aib for most values of τ . However at Aib ∗ , a mimic of Aib where the carbonyl O of Aib is replaced with an imidate N (in 5,6-dihydro-4 H -1,3-oxazine = Oxa), in the peptidomimic Piv-Pro-Aib ∗ -Oxa ( 1 ), the C 5 i structure is persistent in both crystals and in solution. Here we show that the i → i hydrogen bond energy is a more determinant control for the relative stability of the C 5 structure and estimate its value to be 18.5 ± 0.7 kJ/mol at Aib ∗ in 1 , through the computational isodesmic reaction approach, using two independent sets of theoretical isodesmic reactions.

Theoretical investigations have been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CF 3 CH 2 OCH 2 CF 3 and OH radical using a newly developed DFT based M06-2X functional method. Two important H abstraction channels have been identified according to different orientations of the two H atoms bonded to same carbon atom in CH 2 group, and one transition state has been located for each reaction channel. At the entry of each reaction channel, formation of pre-reactive complex indicates an indirect hydrogen-abstraction reaction. The rate coefficients were calculated for the first time over a wide range of temperature (250–1000 K) and can be expressed as a model equation: k OH = 2.55 × 10 −11 exp(− (2883.7 − 387626/ T )/ T ) cm 3 molecule −1 s −1 . At 298 K, our calculated rate coefficient for CF 3 CH 2 OCH 2 CF 3 with OH radical 1.32 × 10 −13 cm 3 molecule −1 s −1 is in very good agreement with the experimental result of k OH = 1.30 × 10 −13 cm 3 molecule −1 s −1 . Using a group-balanced isodesmic reaction, the standard heats of formation for CF 3 CH 2 OCH 2 CF 3 and CF 3 CHOCH 2 CF 3 radical are estimated to be −365.64 and −316.84 kcal mol −1 , respectively. The calculated bond dissociation energy for the C H bond in CF 3 CH(H)OCH 2 CF 3 is found to be 95.82 kcal mol −1 at 298 K. The atmospheric lifetime of CF 3 CH 2 OCH 2 CF 3 was estimated to be around 0.272 years. The global warming potential and the main degradation process of alkoxy radical CF 3 CH(O )OCH 2 CF 3 are also discussed.

A theoretical study on the mechanism and kinetics of the gas phase reactions of CH 3 CH 2 OCF 3 (HFE-263) with the OH radicals and Cl atoms have been performed using meta-hybrid density functional MPWB1K method and 6-31+G(d,p) basis set. Energetics are further refined by calculating the energy of the species with a high level G2(MP2) method. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. The hydrogen abstraction from CH 2 group is found to be the dominant reaction channel for reaction with OH radicals, whereas hydrogen abstraction from CH 3 group is the dominant channel for Cl atoms, especially at higher temperature. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CH 3 CH 2 OCF 3 and radicals generated by hydrogen abstraction, CH 3 CHOCF 3 and CH 2 CH 2 OCF 3 are reported for the first time. The calculated bond dissociation energies for C H bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–1000 K. The G2(MP2) calculated rate constant values are 0.52 × 10 −13 and 0.77 × 10 −12 cm 3 molecule −1 s −1 , respectively for reactions with OH radicals and Cl atoms at 298 K.

The hydrogen abstraction reactions of methyl esters from methyl formate (MF) to methyl decanoate (MD) by hydrogen (H) atom at the methoxy group have been investigated on the basis of isodesmic reactions within the framework of reaction class transition state theory (RC-TST). The rate constants for the four reactions of H with MF, methyl acetate (MA), methyl propanoate (MP), and methyl butanoate (MB) are used as the benchmarking values, and are calculated via the transition state theory (TST) with the Eckart method to account for tunneling effect by employing potential energy surface information computed at the CCSD(T)/CBS//BH&HLYP/6-31G(d,p) level. The calculated rate constants of reactions H with MF and MA are in excellent agreement with experimental results. For the target reactions of H with MA, MP and MB, it is demonstrated that the calculated energy barriers and rate constants at the BH&HLYP/6-31G(d,p) level with a simple correction scheme based on isodesmic reactions within the framework of RC-TST can approach the accuracy of the CCSD(T)/CBS level. Based on the correction scheme, reaction enthalpies, energy barriers and rate constants for large reaction systems including the reactions of H with methyl valerate (MV), methyl hexanoate (MHex), methyl heptanoate (MHep), methyl octanoate (MO), methyl nonanoate (MN) and MD at the methoxy group are computed and fitted into the modified Arrhenius expression in the temperature range 300–2500 K for chemical kinetic modeling studies. Further, it is found that the reaction rate constants of H with large methyl ester molecules (from MA to MD) is nearly identical and is slightly larger than that of H with MF at the methoxy group.

The mechanism and thermodynamic functions of the self-assembly of a family of covalently linked oligomeric naphthalenediimides (NDIs) were investigated through variable-temperature NMR and CD studies. The NDIs were shown to self-assemble into helical supramolecular nanotubes via an isodesmic polymerisation mechanism, and regardless of the oligomer length a surprising entropy-enthalpy compensation was observed.

Naphthalene, polyacenes and graphene are considered aromatic. Existing models for polyacenes predict a linearly increasing aromatic stabilization energy (ASE) and give little insights into their high reactivity and decreasing stability. Graphene’s aromaticity has been studied only qualitatively suggesting alternate Clar’s sextet and two-electrons per ring, and ASE estimates are missing. In this paper, various Enthalpy of Hydrogenation (ΔHhydro) and isodesmic schemes have been proposed and compared for the estimation of naphthalene ASE. Results show that ΔHhydro schemes are simple to design, are equivalent to isodesmic schemes, and unconjugated unsaturated reference systems predict ASE values in agreement with literature reports. Partially aromatic reference systems underestimate ASE. ΔHhydro schemes require calculations for a smaller number of structures, and offer scope for experimental validation, and involve enthalpy differences. Polyacene (X-axis extensions of benzene) ASE estimates (using ΔHhydro scheme) correlate well with experimental instability data and offer new chemical physical insights. ASEs extrapolated from quadratic and logarithmic regression models have been used to estimate the largest polyacene with limiting ASE values. ASE values for Pyrene (Y-axis extension of benzene) and higher analogues (here called pyrene-vertacenes) are estimated using ΔHhydro schemes. Further truncated graphene models and graphene are approximated as combinations of polyacene and pyrene-vertacene units. First ever ASE and molecular sizes (22–255 nM) estimates predict nanometer size ranges for flat graphene in agreement with recent experiments and offer new physical insights. These ASE and size estimates for graphene will prove useful in the design of novel energy (hydrogen) storage, electronic and material science applications.

Qunatum mechanical calculations are carried out on the reactions of CF3CH2CH2CHO (TFB) with OH radical by means of meta hybrid DFT methods. The geometries of the reactants, reaction complex, products and transition states involved in the reaction pathways are optimized at MPWB1 K level of theory using 6-31G(d,p) basis set. Single point energy calculations are performed at MPWB1 K level using extended 6-311+G(3df,2pd) basis set. Using group balanced Isodesmic reactions enthalpy of formation at 298 K ( Δ f H 298 ° ) of reactant and corresponding products are also estimated for the first time by using G2(MP)2 and CBS-QB3 methods. The hydrogen abstraction rate constant for the title reaction are calculated in the temperature range of 250–400 K and atmospheric pressure using the Canonical Transition State Theory (CTST) including tunneling correction. The percentage contributions of all three reaction channels are also reported within temperature range of 250–400 K and atmospheric pressure.

The "alkane branching effect" denotes the fact that simple alkanes with more highly branched carbon skeletons, for example, isobutane and neopentane, are more stable than their normal isomers, for example, n-butane and n-pentane. Although n-alkanes have no branches, the "kinks" (or "protobranches") in their chains (defined as the composite of 1,3-alkyl-alkyl interactions-including methine, methylene, and methyl groups as alkyl entities-present in most linear, cyclic, and branched alkanes, but not methane or ethane) also are associated with lower energies. Branching and protobranching stabilization energies are evaluated by isodesmic comparisons of protobranched alkanes with ethane. Accurate ab initio characterization of branching and protobranching stability requires post-self-consistent field (SCF) treatments, which account for medium range (∼1.5-3.0 Å) electron correlation. Localized molecular orbital second-order Møller-Plesset (LMO-MP2) partitioning of the correlation energies of simple alkanes into localized contributions indicates that correlation effects between electrons in 1,3-alkyl groups are largely responsible for the enhanced correlation energies and general stabilities of branched and protobranched alkanes.

Enthalpies of formation of twenty seven mono substituted nitrobenzenes were calculated employing various DFT and composite methods using atomization approach and two types of isodesmic reactions. The overall best agreement with experiment was achieved by using Gn multilevel techniques. It was found that the best performance among DFT methods within atomization approach demonstrates long range corrected wB97XD level theory. The average absolute deviation value calculated for B3P86/6-311G(d,p) which have been recently reported as an very accurate method for calculating formation enthalpies of poly and mono substituted nitrobenzenes exceeds 50 kcal/mol. Employing of isodesmic reactions tends to it improve estimations of DFT levels, though agreement between theoretical data obtained using this methodology with experiment depends strongly on the type of reaction and the quality of experimental Δ f H 0 ,298 values available for compounds involved in these bond balanced reactions.

The molecular structures, conformational mobilities, harmonic vibrational frequencies and thermochemistry of the FC(O)OOO(O)CF, FS(O2)OOO(O2)SF and FC(O)OOO(O2)SF trioxides were studied by ab initio and density functional methods. The potential energy curves for the internal rotations were calculated using the B3LYP hybrid functional with the 6-311+G(3df) basis set. The equilibrium conformations are characterized by skew structure with dihedral angles COOO and SOOO of about 90º and 95º, respectively. The most stable structures were also calculated using the G3(MP2)B3 and G4(MP2) ab initio methods and with the functional M06-2X/6-311+G(3df). Average standard enthalpies of formation at 298 K derived for FC(O)OOO(O)CF, FS(O2)OOO(O2)SF and FC(O)OOO(O2)SF from isodesmic reactions energies calculated at the G3(MP2)//B3LYP/6-311++G(3df,3pd) and G4(MP2) levels of theory are predicted to be -195.4, -255.6, and -226.5 kcal mol-1. From these values, O-O bond dissociation enthalpies of 25?33 kcal mol-1 were estimated. Fil: Badenes, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentina Fil: Tucceri, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentina Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentina

The hydrogen abstraction reaction of CF3CH2CH2OH + OH has been studied theoretically by dual-level direct dynamics method. The required potential energy surface information for the kinetic calculation was obtained at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level. Five stable conformers of CF3CH2CH2OH have been located. For each conformer, there are three potential H-abstraction sites (Cα, Cβ and –OH), and some of the H atoms can be abstracted by more than one abstraction channel due to the different attack orientations of the incoming OH radical. As a result, 31 distinct Habstraction channels have been identified for the reaction. The individual rate constants for each Habstraction channel were calculated by the improved canonical transition-state theory with smallcurvature tunneling correction (ICVT/SCT), and the overall rate constant was evaluated by the Boltzmann distribution function. It is shown that the calculated rate constant is in good agreement with the available experimental data at 298 K, and exhibits negative temperature dependence with 200–350 K. H-abstraction from the α site dominates the reaction at low temperatures, while the contributions from the β and OH abstractions should be taken into account as temperature increases. The fitted four-parameter expressions within 200–1000 K for the overall rate constants as well as the rate constants from the α, β and OH abstractions were given to provide good estimation for future laboratory investigations. In addition, because of the lack of available experimental data for the product radicals involved in the reactions, their enthalpies of the formation (ΔHf,298°) were predicted via isodesmic reaction at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level.

Following the quest for stable silylenes, we have found high thermodynamic and kinetic viabilities for a series of novel cyclic alkylaminosilylenes [CAASs: including 1 N – 4 N )] over their corresponding cyclic alkylphosphinosilylenes (CAPSs: 1 P – 4 P , respectively), at ab initio and DFT levels, coupled with appropriate isodesmic reactions. Among silylenes scrutinized, 4 N immerged the most promising for its higher singlet–triplet energy difference (Δ E S–T ), wider band gap (Δ E HOMO–LUMO ), higher heat of hydrogenation (Δ E H ), significant resistance to dimerization and resistance to rearrangement to its full valence octet isomer, etc. Unsaturation destabilized 2 N , 3 N , and 3 P through cross conjugation.

ImageFunctional supramolecular systems like carbonyl-bridged triarylamine (CBT) trisamides are known for their long-range energy transport at room temperature. Understanding the complex self-assembly processes of this system allows for control over generated structures using controlled supramolecular polymerization. Here, we present two novel CBT trisamides with (S)- or (R)-chiral side chains which show a two-pathway self-assembly behavior in solution. Depending on the thermal profile during the self-assembly process, two different stable states are obtained under otherwise identical conditions. A kinetically trapped state A is reached upon cooling to 7 °C, via a proposed isodesmic process. In addition, there is a thermodynamically stable state B at 7 °C that is induced by first undercooling to −5 °C, via a nucleation-elongation mechanism. In both cases, helical supramolecular aggregates comprising H-aggregated CBTs are formed. Additionally, controlled supramolecular polymerization was achieved by mixing the two different states (A and B) from the same enantiomer, leading to a conversion of the kinetically trapped state to the thermodynamically stable state. This process is highly enantioselective, as no conversion is observed if the two states consist of opposite enantiomers. We thus show the importance and opportunities emerging from understanding the pathway complexity of functional supramolecular systems.

Isodesmic reactions and the energy of intramolecular interactions in bromoalkoxycyclohexanes (alkoxy = OMe, OEt, OiPr and OtBu) were computed to evaluate the effect of bromine and alkoxy groups when bonded together in a cyclohexane ring to give cis and trans-1,2, 1,3 and 1,4 isomers. According to the enthalpy energies obtained from the isodesmic reactions, the bromine atom is preferred to be introduced axially in methoxycyclohexane to give trans-1-bromo-2-methoxycyclohexane; otherwise, equatorial introduction of the bromine atom is favoured. Either direct or indirect intramolecular interactions involving OR and Br, obtained from comparison with the conformational energies of the monosubstituted cyclohexanes, indicate a preference for bromine axially oriented, except for the cis-1,3 isomer, in which the OR and Br groups experience high steric hindrance to each other. The effect of R is generally invariant.

The amide group plays an important role in the structure of proteins and is one of the major functional groups in organic chemistry. Although a large number of investigations were devoted to understanding the chemical character of the amide bond, little is known about the N C bond dissociation enthalpies (BDEs), which represent one of the fundamental sets of chemical thermodynamic data. In this study, the homolytic N C BDEs have been calculated for 55 amides and the effect of substituents on the strength of N C bond has been investigated using the Gaussian-4 (G4) method. The atomization reaction and isodesmic reaction procedures were used for accurate evaluations of enthalpies of formation of parent molecules and radicals derived from them by the breaking of the amide bond. It is demonstrated that the G4 method reproduces the experimental data with high accuracy in most cases. The large discrepancies between experimental and theoretical values revealed in some cases could be due to possible experimental errors. More reliable enthalpies of formation are recommended for 10 molecules and 9 radicals based on quantum chemical calculations. The accurate and internally consistent values of enthalpies of formation of amide molecules and corresponding radicals were used to calculate the N C BDEs. The trends observed in BDEs are associated with substituents on nitrogen and carbonyl. The electron-donating substituents ( C(O) , NHC(O) , O , N 3 ) on carbonyl increase the BDE; these groups, therefore, have stabilizing effect on amide bond. However, the methyl and phenyl substituents on nitrogen result in a decrease of 10–90 kJ/mol in BDEs on going from primary to tertiary amides and, therefore, cause the amide bond to weaken. The observed BDE trends correlate with the N C bond lengths. Nitrogen atomic charges and second-order stabilization energy estimates obtained by NBO analysis can be also used to uncover trends in BDEs and build qualitative descriptions.

Hypohomodesmotic reaction schemes, as described by Wheeler et al. [J. Am. Chem. Soc. 131 (2009) 2547] for the determination of enthalpies of formation (ΔHf,298) for hydrocarbons, have been extended to include sulfur. The impact of hypohomodesmotic schemes, in comparison to the atomization energy approach, upon the determination of enthalpies of formation for organosulfur compounds has been assessed. The gas phase ΔHf,298 of 43 organosulfur compounds have been calculated using the correlation consistent Composite Approach (ccCA), Gaussian-3 (G3), and Gaussian-4 (G4) methodologies using proposed hypohomodesmotic reaction mechanisms and an atomization energy approach. Effects of method and basis set combinations for these schemes have also been assessed.

In this work, the properties of the dinitro-triazole-based high nitrogen compounds were studied theoretically to facilitate further developments. The gas-phase heats of formation were predicted based on the isodesmic reactions by using the DFT-B3PW91/6-31G(d,p) method. The solid-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. The designed molecules show solid-phase heats of formation above 180.0 kcal/mol. The crystal density has been computed using molecular packing calculations with CVFF force field. Detonation properties of the designed compounds were evaluated by using the Kamlet–Jacobs equation based on predicted densities and heats of formation. Designed triazole-based derivatives show detonation velocity ( D ) over 8.3 km/s and detonation pressure ( P ) above 30 GPa. Thermal stability was evaluated via bond dissociation energies (BDEs) of the weakest C–NO 2 bond at B3PW91/6-31G(d,p) level. Bond dissociation energy analysis revealed that designed molecules are better candidates considering stability.