Bond Dissociation Energy Values Research Articles

Quantitative assessment of reparameterized PM6 (rPM6) for hydrogen abstraction reactions

In the present study, the usability of semiempirical quantum mechanical methods for calculating bond dissociation energy (BDE) was investigated systematically. Density functional theory (DFT) methods with the B3LYP and B97-1 functionals were used for comparison. We introduced a new test set for BDE, called BDE200, which covers a wide range of compounds including large aromatic compounds. The use of BDE200 test set revealed that the accuracy of the methods studied was ordered from best to worst as: B97-1 > B3LYP > rPM6 >> PM7 > PM6 > AM1 > PM3. In addition to the improved accuracy of rPM6 for predicting BDE, it was found that rPM6 can provide a quantitative correlation between BDE values and reactivity. The rPM6 calculated activation enthalpies for C–H hydroxylation catalysed by the compound I of cytochrome P450 were proportional to the calculated and experimental C–H BDE values, in line with the results of previous DFT studies. We believe that rPM6 can help develop a database, for instance, for the determination of site of metabolism.

Substituent effects on antioxidant activity of monosubstituted indole‐3‐carbinols: A DFT study

AbstractIndole‐3‐carbinol (I3C) is an indole compound with proven health benefits and thus potential preventive medicine and therapeutic applications. Here the origins of the substituent effects on the antioxidant activity of monosubstituted indole‐3‐carbinols (I3Cs) were studied in silico by calculating their thermochemical properties using the (RO)B3LYP/6‐311++G(2df,2p)//B3LYP/6‐311G(d,p) model chemistry. It was found that the electron withdrawing groups such as CF3, CN, COOH, COOMe can increase the bond dissociation energy (BDE) values of N‐H bonds and decrease the BDE(C8‐H) values, while the presence of the Br, Cl, F, Me, NMe2, NH2, NHMe, OH, OMe, Ph groups seems to decline the BDE(X‐H)s (X = N, C). It is worth noticing that a sequential electron transfer mechanism is responsible for these I3Cs with the strong electron donating groups including NMe2, NHMe and NH2, while a hydrogen atom transfer mechanism is likely favored for the remaining monosubstituted I3Cs. The kinetic study according to the HAT mechanism showed that the CH3OO• radical scavenging of 2‐NMe2‐I3C derivative has the highest rate constant (k = 1.93×1010 M‐1s‐1) and it is higher than that of typical antioxidants i.e. Trolox or ascorbic acid. Thus, the results appear to suggest that the N‐Br‐I3C and 2‐NMe2‐I3C compounds are potential antioxidants.

Carbon‐centered radical initiators for polymerization of unsaturated monomers: Modeling and reactivity studies

A series of sterically encumbered diphenylethane molecules was examined to understand their fundamental ability to undergo homolytic bond cleavage and initiate radical polymerization of unsaturated monomers. The structures computed by density functional theory (DFT) showed a relationship between increasing C‐C bond length of the ground state molecule and reduced bond dissociation energy (BDE). The computed activation barriers associated with radical addition to acrylate were relatively low indicating that once radicals were formed, initiation of polymerization would be facile. Good correlations between computed BDE and experimentally‐determined onset temperatures for acrylate polymerization were found. The Molecule (13) with the lowest BDE (33.8 kcal/mol) determined in this work had an onset temperature of 85 °C. Ethylene polymerization failed to show a similar trend as molecules possessing the weakest C‐C bonds did not effectively initiate ethylene polymerization. Theoretical calculations demonstrated a trend in which the molecules with the lowest BDEs had the highest barriers for addition of ethylene. These barriers were significantly higher than standard peroxide initiation or chain propagation. Upon ramping the temperature, it is postulated that molecules with low BDE values form radicals but do not have sufficient energy to add to ethylene before succumbing to detrimental side‐reactions. POLYM. ENG. SCI., 59:E52–E58, 2019. © 2018 Society of Plastics Engineers

Theoretical and experimental analysis of the antioxidant features of substituted phenol and aniline model compounds

Although natural polyphenols have attracted extended attention as antioxidants, there is only limited information available on their structure-activity relationship (SAR). In addition, while often having significant antioxidant activity, amino group-containing compounds have only been sporadically studied. Often, the complex structure makes studying the individual contribution of aromatic OH or NH2 groups on the activity of these antioxidants difficult. In this work, several substituted simple phenols and anilines were selected as model compounds. Both the experimental radical scavenging activity and major structural descriptors have been determined to gain more insights into the potential SAR. Physicochemical properties pertaining to energetic and structural parameters were determined and experimental data gathered from three antioxidant assays to identify fundamental features with reasonable effect on antioxidant activity. Density functional theory (DFT) calculations were carried out at the B3LYP/6-31G(d,p) level to determine the N–H and O–H bond distances, dipole moments, logP values, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbital energies, HOMO-LUMO gaps, radical spin densities, proton affinities, and ionization potentials. The compounds were screened for activity against the 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 2,2-diphenyl-1picrylhydrazyl (DPPH), and peroxyl (ORAC assay) radicals. Based on the results, ABTS antioxidant activity was selected for further investigations to observe correlations with the calculated properties. The HOMO energies, bond-dissociation energy values, HOMO-LUMO gap energies, dipole moment, proton affinity, and the Hammett constants appear to show meaningful correlation with the experimental data.

A systematic electronic structure study of the O–O bond dissociation energy of hydrogen peroxide and the electron affinity of the hydroxyl radical

Hydroxyl radical reduction and peroxide bond breaking in hydrogen peroxide are reactions involved in various processes such as the Fenton reaction, which has applications as e.g. groundwater remediation. Here, we study these two reactions from a thermodynamical point of view through the bond dissociation energy (BDE) of the O–O bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. High-level ab-initio calculations at the complete basis set (CBS) limit were carried out, and the performance of different DFT-based methods was addressed by following a specific classification on the basis of the Jacob’s ladder in combination with various Pople’s basis sets. The ab-initio calculations at the CBS limit are in agreement with experimental reference data and identify a significant contribution of the electron correlation energy to the BDE and EA. The studied DFT-based methods were able to reproduce the ab-initio reference values, although no functional was particularly detected as the best for both reactions. The inclusion of certain percentage of Hartree–Fock (HF) exchange in DFT functionals leads in most cases to smaller BDE and EA values, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF methods with an accuracy comparable to the MP2 or CCSD level of theory. Additionally, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the errors in the angles were between one and two degrees with some systematic trend with respect to the basis set’s size. From our results we conclude that DFT methods present a computationally less expensive alternative to describe these two reactions that play a role in the Fenton reaction. The benchmark that is carried out in this study provides a systematic validation of various approximated $$E_{xc}[\rho ]$$ functionals combined with different basis sets, which could serve as a stepping-stone for future research on the Fenton reaction.

Comparing Protonolysis and Transmetalation Reactions: Microcalorimetric Studies of C-AuI Bonds in [AuRL] Complexes.

The protonolysis of C-Au bonds in [AuRL] organometallic complexes has been studied by calorimetry for 12 R groups. The experimental data have been combined with density functional theory calculations to obtain bond dissociation energy (BDE) values. The C-Au BDE values show a good correlation with the corresponding isolobal C-H BDE values. The heat released in the protonolysis of [AuRL] has also been measured for R = Ph and L = P(OPh)3, PPh3, PMe3, PCy3, and IPr, and these values strongly depend on the trans influence of L because of the mutual destabilization of the L-Au and Au-C bonds. The enthalpies of the transmetalation reaction [AuR(PPh3)] + SnIBu3 → [AuI(PPh3)] + SnRBu3 for seven R groups have been measured and compared with those of the corresponding [AuR(PPh3)] protonolysis.

Accurate theoretical method for homolytic cleavage of C[sbnd]Sn bond: A benchmark approach

Stille coupling is a well-known cross coupling reaction, where the rate determination step is the dissociation of carbon stannous (CSn) bond. The organotin compounds are also used as precursors in the manufacturing of tin oxide films, solar cells, gas sensors, flat panel display technology and low emission glass materials, etc. The reactivity of organotin compounds has direct relationship with the homolytic cleavage of CSn bond. Therefore, accurate determination of CSn bond has direct relevance in understanding many phenomena. The current benchmark study is aimed at finding out the accurate theoretical method for the homolytic cleavage (bond dissociation energy) of CSn bond. In this regard, nineteen DFs from eight different classes of DFT with two effective core potential basis sets (LANL2DZ and SDD) and two Karlsruhe basis sets (def2-SVP and def2-TZVP) are selected for the BDE calculation of CSn bond. Ten structurally diverse organotin compounds with experimentally known BDE of CSn bond are selected from the literature. The statistical [root mean square deviation (RMSD), standard deviation (SD), Pearson’s correlation (R) and mean absolute error (MAE)] results are obtained by the comparison of theoretical data with the experimental BDE values of CSn bond of selected organotin compounds. Among all DFT classes, GGA-D class is a batter class and BLYP-D3 functional of this class is selected as the best functional for homolytic bond dissociation energy (BDE) calculation of CSn bond. This functional with SDD basis set shows remarkable performance in reproducing the BDE of CSn bond with more accuracy. The SD, RMSD, R and MAE are 4.11 kcal mol−1 is 3.9 kcal mol−1 is 0.963 and −0.01 kcal mol−1, respectively.

The natural food colorant Peonidin from cranberries as a potential radical scavenger – A DFT based mechanistic analysis

A theoretical evaluation of the antioxidant property of a natural food colorant Peonidin has been performed. The most suitable mechanism for explaining the radical scavenging capacity of Peonidin is the Hydrogen Atom Transfer and the most active site for radical formation is position 3 and is confirmed through Mulliken charge analysis, pKa value evaluation, Bond Dissociation Energy values, and Natural Bond Orbital analysis. Position 3 and 5 in Peonidin exists in blood as deprotonated as their pKa values are lower than the pH of blood. Peonidin is highly reactive than Quercetin and less stable than flavan-3-ols due to the small band gap. Global descriptor analysis shows that PN prefers to accept electrons than to donate. The effect of number of OH groups and the nature of substituents are well explained through this work.

Molecule and Synthesis Design of a Family of High Energy Density Materials Based on “565” Chemical Structure

AbstractA family of high energy density materials based on “565” chemical structure were designed and the spatial structure, heat of formation, detonation velocity, detonation pressure and sensitivity of each compound were investigated systematically by density functional theory. The results show that all the designed molecules possess high positive heat of formation (from 336.8 to 4135.7 kJ mol−1) and moderate detonation properties (detonation velocities range from 6.15 to 11.69 km s−1 and detonation pressures range from 16.4 to 68.28 GPa). Based on the values of detonation properties, impact sensitivities (range from 6.8 to 54.3 cm) and bond dissociation energies (range from 30.7 to 402.6 kJ mol−1), compounds A1, A2, A4 and B4 were selected as the potential high energy density materials. Then frontier molecular orbital, electrostatic potential on the surface and thermal dynamic parameters of these selected molecules were simulated to give a better understanding of their chemical and physical properties. Also, a reasonable synthetic path of the selected molecules were provided for further experimental synthesis and testing.

Computational study of the structure and properties of bicyclo[3.1.1]heptane derivatives for new high-energy density compounds with low impact sensitivity.

To design new high-energy density compounds (HEDCs), a series of new bicyclo[2.2.1]heptane derivatives containing an aza nitrogen atom and nitro substituent were designed and studied theoretically. The density, heat of sublimation and impact sensitivity were estimated by electrostatic potential analysis of the molecular surface. Based on the designed isodesmic reaction, and the reliable heat of formation (HOF) of the reference compounds, HOFs were calculated and compared at B3LYP/6-311G(d,p) and B3P86/6-311G(d,p), respectively. The detonation performances, bond dissociation energies (BDE) and impact sensitivity were calculated to evaluate the designed compounds. The calculated results show that the number of aza nitrogen atoms and NO2 groups are two important factors for improving HOF, density and detonation properties. Thermal stability generally decreases with increasing nitro groups. And the N-NO2 bond is the trigger bond for all designed compounds except B8, whose trigger bond is C-NO2. Importantly, the BDE values are between 86.95 and 179.71kJmol-1 and meet the requirement for HEDCs. Detonation velocity and detonation pressure were found to be 5.77-9.65kms-1 and 12.30-43.64GPa, respectively. After comprehensive consideration of thermal stability, impact sensitivity and detonation properties, A7, A8, B8, C8, D7, E7, F7 and G6 may be considered as potential HEDCs. Especially, A8, B8, C8, and D7 have better detonation properties than the famous caged nitramine CL-20 (D = 9.40km/s, P = 42.00GPa). Besides, all the designed potential HEDCs have reasonable impact sensitivity. Graphical abstract New high-energy density compounds (HEDCs) with low impact sensitivity (A8, B8, C8 and D7 have better detonation properties than CL-20).

Corrigendum: Acid-Mediated Formation of Radicals or Baeyer-Villiger Oxidation from Criegee Adducts.

An error has occurred in this Communication, the calculated bond dissociation energies (BDE) of compounds 15 a and 15 b have been mixed up. The corrected Figure 1 with the correct values is shown below. The discussion of the manuscript and its conclusions remain unchanged. O−O bond dissociation enthalpies (BDE) of peroxide species potentially formed under the reaction conditions; calculated in vacuum using the wB97XD functional with the aug-cc-pVTZ basis set. In the same way, the BDE values for 15 a and 15 b have been mixed up in Table S3 of the Supporting Information. Additionally, the enthalpies of some structures reported in Table S6 have to be corrected, since they were actually calculated using geometries and vibrational frequencies obtained with the larger basis set aug-cc-pVTZ, instead of 6-31++G(d,p), as indicated. However, the changes are small (as the final electronic energies are computed using the larger basis set in both cases) and will not change the conclusions. Also, in Figure 2 of the manuscript, the correct values had been used. A corrected version of the Supporting Information is available along with this Corrigendum. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A Spinning Umbrella: Carbon Monoxide and Dinitrogen Bound MB12- Clusters (M = Co, Rh, Ir).

Strong binding of carbon monoxide (CO) and dinitrogen (N2) by MB12- (M = Co, Rh, Ir) clusters results in a spinning umbrella-like structure. For OCMB12- and NNMB12- complexes, the bond dissociation energy values range within 50.3-67.7 kcal/mol and 25.9-35.7 kcal/mol, respectively, with the maximum value obtained in Ir followed by that in Co and Rh analogues. COMB12- complex is significantly less stable than the corresponding C-side bonded isomer. The associated dissociation processes for OCMB12- and NNMB12- into CO or N2 and MB12- are highly endergonic in nature at 298 K, implying their high thermochemical stability with respect to dissociation. In OCMB12- and NNMB12- complexes, the C-O and N-N bonds are found to be elongated by 0.022-0.035 Å along with a large red-shift in the corresponding stretching frequencies, highlighting the occurrence of bond activation therein toward further reactivity due to complexation. The obtained red-shift is explained by the dominance of L←M π-back-donation (L = CO, OC, NN) over L→M σ-donation. The binding of L enhances the energy barrier for the rotation of the inner B3 unit within the outer B9 ring by 0.4-1.8 kcal/mol, which can be explained by a reduction in the distance of the longest bond between inner B3 and outer B9 rings upon complexation. A good correlation is found between the change in rotational barrier relative to that in MB12- and the energy associated with the L→M σ-donation. Born-Oppenheimer molecular dynamics simulations further support that the M-L bonds in the studied systems are kinetically stable enough to retain the original forms during the internal rotation of inner B3 unit.

Experimental bond dissociation energies of benzylpyridinium thermometer ions determined by threshold-CID and RRKM modeling

Benzylpyridinium salts (BPs) have often been used as thermometer ions to obtain an energy calibration of mass spectrometric experiments (in particular to determine internal energy distributions of ions after the ionization process). Fragmentation of BP+ molecular ions is characterized by specific Bond Dissociation Energies (BDE) which depend on the substituent group and its location on the benzyl ring. Although those BDE values are regularly re-evaluated by quantum chemical calculations, their experimental determination is still missing from the literature. In this paper, a modified Quadrupole-hexapole-Quadrupole (QhQ) mass spectrometer is used to obtain such values on 4 BP+ molecular ions (characterized by a wide range of CN bond strengths) using Threshold Collision-Induced Dissociations (TCID) and Rice–Ramsperger–Kassel–Marcus (RRKM) kinetic modeling. It is found that experimental values are systematically 0.5eV lower than their most recent theoretical evaluations. Despite this shift, the absolute critical energy values are maintained in the same order (pOMe<pMe<pCl<pCN), and the relative energy differences are in very good agreement. We argue that the observed 0.5eV shift relates to the energy dependence of the Transition State’s number of states that is typical for barrier-less fragmentation processes and, relates to a kinetic rather than an energetic bottleneck. Notably, by taking into account the bond elongations characterizing the transition states and their corresponding calculated critical energies (E0), close agreement is found with experimentally obtained E0 values. We thus conclude that much care should be taken when describing the transition state during an internal energy calibration procedure where the involved energy is lower than 3–4eV.

N-Acetyl-cysteine Increases Chemical Stability of Hydroquinone in Pharmaceutical Formulations: a Theoretical and Experimental Approach

In this study, the chemistry stability of hydroquinone (HQ) was evaluated according to its effects in redox properties and compared to kojic acid (KA). The HQ oxidation was more inhibited by N-acetylcysteine (NAC) than ascorbic acid (AA). These results were elucidated using theoretical methods at the DFT/B3LYP level of theory. All electronic parameters were related between antioxidant performance and highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), HOMO-LUMO value gap (GAP), ionization potential (IP), and phenol or enol bond dissociation energy (BDEOH) values. However, the interactions between HQ and NAC cannot be related by changing of these electronic parameters. Therefore the high calculated values for electron transfer can be associated to NAC due to polarizability or chelation properties of sulfur moiety.

Palladium-catalyzed intramolecular reductive olefin hydrocarbonation: benzylic hydrogen serving as a new hydrogen donor.

A palladium-catalyzed intramolecular hydrocarbonation of unactivated alkenes was achieved, in which toluene is used as a hydrogen donor for the first time. The radical transfer hydrogenation is designed and realized based on the Bond Dissociation Energy (BDE) value. A toluene derivative, which is cheap, readily available and easy to handle, serves as a new hydrogen donor in radical involved reactions, providing a novel and promising perspective for future reductive reactions.

On the formation of SFn– (n = 1–6) anions via a novel route and their properties

Sulfur hexafluoride (SF6 ) being a potential greenhouse gas, coupled with its numerous applications, makes the study of the formation and fragmentation of SF6 -based species important. The formation of SF6 -based anionic species has been studied using the gas feed-sputtering route and the mechanisms at play during the sputter-ejection of guest molecule-derived particles have also been probed. Studies of the formation of SFn (-) (n = 1-6) anions were conducted from various surfaces (metal and compound) that were subjected to Cs(+) ion sputtering in the presence of SF6 gas employing the gas feed-cesium sputter technique. The anions generated were mass analyzed using a double-focusing magnetic sector mass spectrometer. Quantum mechanical computations were performed to study the ground state structure and stability of neutral and negatively charged SFn (n = 1-6) systems applying density functional theory (DFT) and ab initio methods (MP2 and CC). This technique readily generated (32) SFn (-) (n = 1-6) anions for all sizes of 'n' with practicable yields. Mass spectrometric measurements of the yield of sputter-ejected (32) SFn (-) (n = 1-6) anions reveal an oscillatory pattern as a function of 'n', with odd values of 'n' being relatively more abundant. The relative yield of (34) SFn (-) (n = 1-6) anions with respect to size was also measured albeit with low signal intensity. Also observed were F(-) , S(-) , F2 (-) , (33) SF5 (-) and (33) SF6 (-) anionic species. The relevant electron affinity and bond dissociation energy (BDE) values were also computed. Gas-phase SFn (-) (n = 1-6) anions can be effectively generated by using the gas spray-cesium sputter technique. Both experimental measurements and calculations indicate the existence of odd-even oscillations in the stability and electronic structure of the SFn (n = 1-6) systems. The highest yield recorded was for the sputter-ejected SF5 (-) species and this may be attributed to its 'superhalogen' anionic character coupled with the relatively favorable F(0) fragmentation pathway of sputtered SF6 (-) . A signature pertaining to intact SF6 (-) anion ejection is also observed.

Kinetics and thermodynamics of 1-hydroxyethyl radical reaction with unsaturated lipids and prenylflavonoids.

Hydroxyalkyl radicals have been reported to induce lipid oxidation as the key aspect of the pathogenesis of alcoholic fatty liver disease and are responsible for the alkylation and cleavage of DNA during the metabolism of a wide range of genotoxic compounds. However, relevant kinetic data for the oxidation of unsaturated lipids by 1-hydroxyethyl radical (HER) has not been reported. In this study, the rate constants for the reaction of unsaturated fatty acid methyl esters and sterols with HER have been determined using a competitive kinetic approach employing the spin-trap α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) as the competitive substrate. Polyunsaturated fatty acid methyl ester is shown to react with HER with an apparent second-order rate constant ranging from (3.7 ± 0.1) × 10(6) L mol(-1) s(-1) for methyl linoleate to (2.7 ± 0.2) × 10(7) L mol(-1) s(-1) for methyl docosahexanoate at 25.0 ± 0.2 °C in ethanol. The apparent second-order rate constant for polyunsaturated fatty acid methyl ester oxidation by HER is dependent on the number of bisallylic hydrogen atoms rather than on the bond dissociation energy value for the weakest C-H bond as determined by ab initio density functional theory calculations. Sterols displayed higher reactivity compared to unsaturated fatty acid methyl esters with apparent second-order rate constants of (2.7 ± 0.1) × 10(6) and (5.2 ± 0.1) × 10(7) L mol(-1) s(-1) at 25.0 ± 0.2 °C in ethanol for cholesterol and ergosterol, respectively. Similar experiments with prenylflavonoids as potential herbal chemopreventive agents for preventing alcoholic liver diseases yield apparent second-order rate constants close to the diffusion control with kapp values of (1.5 ± 0.2) and (3.6 ± 0.1) × 10(9) L mol(-1)s(-1) for 6-prenylnarigerin and xanthohumol at 25.0 ± 0.2 °C in ethanol solution, respectively. Polyunsaturated lipids were revealed to be highly reactive oxidizable substrates toward HER-induced oxidation in biological systems leading to damage of membranes and sensitive structures.

Aerobic oxidation of alkylaromatics using a lipophilic N-hydroxyphthalimide: overcoming the industrial limit of catalyst solubility.

4,4'-(4,4'-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO-H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated.

Quantitative Assessment of the Multiplicity of Carbon–Halogen Bonds: Carbenium and Halonium Ions with F, Cl, Br, and I

CX (X = F, Cl, Br, I) and CE bonding (E = O, S, Se, Te) was investigated for a test set of 168 molecules using the local CX and CE stretching force constants k(a) calculated at the M06-2X/cc-pVTZ level of theory. The stretching force constants were used to derive a relative bond strength order (RBSO) parameter n. As alternative bond strength descriptors, bond dissociation energies (BDE) were calculated at the G3 level or at the two-component NESC (normalized elimination of the small component)/CCSD(T) level of theory for molecules with X = Br, I or E = Se, Te. RBSO values reveal that both bond lengths and BDE values are less useful when a quantification of the bond strength is needed. CX double bonds can be realized for Br- or I-substituted carbenium ions where as suitable reference the double bond of the corresponding formaldehyde homologue is used. A triple bond cannot be realized in this way as the diatomic CX(+) ions with a limited π-donor capacity for X are just double-bonded. The stability of halonium ions increases with the atomic number of X, which is reflected by a strengthening of the fractional (electron-deficient) CX bonds. An additional stability increase of up to 25 kcal/mol (X = I) is obtained when the X(+) ion can form a bridged halonium ion with ethene such that a more efficient 2-electron-3-center bonding situation is created.

Antioxidant potential of orientin: A combined experimental and DFT approach

The antioxidant activity of the bioactive fractions obtained from the leaves of Rhynchosia capitata is evaluated for its capacity to reduce ferric ions. In vitro antihemolytic analysis for the separated erythrocytes of Wistar rat blood cells exhibits maximum inhibition value for ethyl acetate (1202.55±9.46) than ethanol fraction (424.57±12.04). Gas and solvent phase studies of structural and molecular characteristics of C-glycosyl flavonoid, orientin present in the bioactive fraction of R. capitata is investigated through hydrogen atom transfer mechanism (HAT) using DFT/B3LYP/6-311G(d,p) level of theory. Interestingly, the intramolecular hydrogen bonding formed between 3′-O and 4′-H makes 3′-OH as the active site which is supported by its bond dissociation energy values. The computed values of the adiabatic ionization potential, electron affinity, hardness, softness, electronegativity and electrophilic index indicate that orientin possess good radical scavenging activity. In this study, role of molecular electrostatic potential and electron density distribution map in predicting the importance of B-ring are analyzed and reported. Spin density distribution analysis for the radicals is formed by summing of spin on rings A, B and C. The most active system able to transfer a hydrogen atom is orientin compared to vitexin and the bond dissociation enthalpy follows the order benzene>ethyl acetate>water.