The C−NO2 bond dissociation energies of some nitroaromatic compounds: DFT study

The C−NO₂ bond dissociation energies in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene; 2-methyl-nitrobenzene; 4-methyl-nitrobenzene; and 1,3,5-trinitrobenzene nitroaromatic molecules, are computed using B3LYP, B3PW91, B3P86 three-parameter hybrid Density Functional Theory (DFT) methods in conjunction with 6-31G^** basis set. By comparing the computed energies and experimental ones, it is found that B3P86/6-31G^** is not capable of predicting the satisfactory bond dissociation energy (BDE). The BDEs computed with both B3LYP/6-31G^** and B3PW91/6-31G^** for the nitroaromatic molecules are closer to the experimental ones than those obtained with B3P86/6-31G^**. But, when compared with the experimental one, the BDE from the B3LYP/6-31G^** has the maximum deviation, which is completely outside our desired target accuracy for chemical predictions (less than 2.00 kcal mol⁻¹). Therefore, we suggest B3PW91/6-31G^** method as a reliable method of computing the BDE for removal of the nitrogen dioxide group in the nitroaromatic compounds. In addition, the C−NO₂ BDEs for 2,4,6-trinitrotoluene (TNT), triaminotrinitrobenzene (TATB), diaminotrinitrobenzene (DATB), and picramide are studied with B3PW91/6-31G^** method.     

High level ab initio and density functional theory study of bond selective dissociation of CH3SH and CH3CH2SH radical cations

Selective bond dissociation energies for CH₃SH and CH₃CH₂SH radical cations were evaluated with G1, G2, G2MP2, B3LYP, BLYP, and SVWN computational methods. It was determined that both G2 and CBSQ evaluate very accurate bond dissociation energies for thiol radical cations, while gradient-corrected BLYP computes the best energies of three employed DFT methods. For the CH₃CH₂SH radical cation, new, higher than previously estimated selective bond dissociation energies were suggested. Received: 10 September 1997 / Accepted: 9 September 1998 / Published online: 11 November 1998     

AM1 calculations of bond dissociation energies. Allylic and benzylic C-H bonds

AM1 method and correlation dependence between electronic relaxation energy and valence change on the C atom of the breaking bond were used to calculate the bond dissociation energies in 50 compounds with allylic or benzylic C-H bonds. The average calculation error is 0.8 kcal/mol.     

The scalar relativistic contribution to gallium halide bond energies

The one-electron Douglas–Kroll (DK) and perturbation theory (+R) approaches are used to compute the scalar relativistic contribution to the atomization energies of GaF _n . These results are compared with previous GaCl _n results. While the +R and DK results agree well for the GaCl _n atomization energies, they differ for GaF _n . The present work suggests that the DK approach is more accurate than the +R approach. In addition, the DK approach is less sensitive to the choice of basis set. The computed atomization energies of GaF₂ and GaF₃ are smaller than the atomization energies from the somewhat uncertain experiments. It is suggested that additional calibration calculations for the scalar relativistic effects in GaF₂ and GaF₃ would be valuable. Received: 20 November 1998 / Accepted: 21 December 1998 / Published online: 16 March 1999     

Determination of bond dissociation energies using mass spectrometry

Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR/MS) offers the opportunity for gas phase cluster formation reactions at very low pressures and at temperatures that are different from room temperature. Reactions take place with single positive‐charge metal ions that are normally +2, +3, +4, etc., charged in solution. The ions formed are detected by measuring the current induced by their cyclotron rotation, but they cannot be physically separated and collected. Collision‐induced dissociation (CID) is widely used for ion‐structure determination via the fragmentation of the excited ions. CID study aims to determine the relationship between the V_pp [peak‐to‐peak voltage of the radiofrequency (rf) pulse] and the mass‐to‐charge (m/z) ratio, which will be used for the calculation of the center‐of‐mass translational kinetic energy (Ek_cm) of the excited ion under investigation. CID studies are restricted to stable ions with relatively high abundance. Nevertheless, with the evolution of computational chemistry, such problems can be overcome whereby CID calculations will be used to provide the substantial parameters for computer software, such as the Gaussian 03 program, for the structure determination of the less stable Ni_xS anions. The latter constitutes the core for our current research. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Correlations between F NMR chemical shifts and bond dissociation energies, enthalpies of formation and group electronegativities

Correlations between ¹⁹F NMR chemical shifts (Φ) in fluorohalohydrocarbons and enthalpies of formation, bond dissociation energies, group contribution to enthalpies of formation and enthalpies of formation of free radicals are presented. A good correlation between these properties has been found with the square root of Φ. A relationship between fluorine chemical shifts and group electronegativities is also discussed.     

Spectroscopic calculations of CH and OH bond dissociation energies for aldehydes, ketones, acids, and alcohols

CH and OH bond dissociation energies were calculated by the spectroscopic and quantum-chemical methods for aldehydes, ketones, acids, and alcohols. The spectroscopic values of CH and OH bond dissociation energies were obtained from the fundamental absorption bands by the variational method in an anharmonic approximation using the Morse-anharmonic basis set. Quantum-chemical calculations were carried out using the 6-311G(3df,3pd)/B3LYP basis set. It is discussed how the bond dissociation energies change with the structure of the molecule.     

Computational studies of bond dissociation energies, ionization potentials, and heat of formation for NH and NH+. Are hybrid density functional theory methods as accurate as quadratic complete basis set and Gaussian-2 ab initio methods?

Ionization potentials, bond dissociation energies, and heat of formation for NH and NH⁺ molecular species as well as for their elements were computed with highly reliable quadratic complete basis set and Gaussian-2 ab initio methods. The results are compared with experimental results and the assurance of these ab initio approaches is assessed. The same studies were also performed with three hybrid density functional methods (B3LYP, B3P86, and B3PW91) in combination with variously sized basis sets. The computational results are discussed in light of density functional theory reliability for exploring the potential energy of small polar molecular systems. Received: 21 July 1997 / Accepted: 8 December 1997     

Quantum Monte Carlo calculations of bond dissociation energies for some nitro and amino molecules

Bond dissociation energies (BDEs) for some nitro or amino contained prototypical molecules in energetic materials are computed by fixed‐node diffusion quantum Monte Carlo method. The nodes are determined from a Slater determinant calculated within density functional theory at the B3LYP/6‐311G** level. The possible errors, the nodal error, and the cancellation of nodal errors in calculating BDE are discussed, and the accuracy is compared with other available ab initio computations and experimental results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Population analysis based on occupation numbers II. Relationship between shared electron numbers and bond energies and characterization of hypervalent contributions

The population analysis based on occupation numbers, originally proposed by Davidson, is briefly reviewed. A new way is proposed to determine modified AOs and to characterize hypervalent contributions. This is discussed in application to the molecules NSF, NSF₃, SF₆, OPCl, OPCl₂, O₂PCl, SO₂, ClO ₄ ^– . It is the main objective of this work to investigate the connection between shared electron numbers — considered as a measure of covalent bond strength — and bond energies, is found to be a reliable measure of bond energies.     

A theoretical study of five nitrates: Electronic structure and bond dissociation energies

Three density-functional methods (B3P86, B3PW91, and B3LYP) are employed to investigate the O–NO₂ bond lengths, frontier orbital energies, and O–NO₂ bond dissociation energies (BDEs) of n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), triethylene glycol dinitrate (Tri-EGDN), and tetraethylene glycol dinitrate (Tetra-EGDN). It is found that the O–NO₂ bond lengthens (destabilizes) in the order of IPN, NPN, EHN, Tetra-EGDN, and Tri-EGDN. From the data of frontier orbital energies (E_HOMO, E_LUMO), and energy gaps (ΔE), we estimate the relative thermal stability ordering of five nitrates and their corresponding radicals. The predicted BDEs of O–NO₂ bond in NPN, IPN, EHN, Tri-EGDN, and Tetra-EGDN, are 176.6, 174.5, 168.1, 156.1, and 159.3 kJ mol⁻¹, respectively. Based on the finding that the present results of BDEs are well coincident with the experimental results of apparent activation energies from the literature, we can draw a conclusion that the experimental thermolysis of five nitrates is only unimolecular homolytical cleavage of the O–NO₂ bonds.     

木质素模化物键离解能的理论研究

采用密度泛函理论B3P86方法,在6-31G(d,p)基组水平上,对木质素结构中的6种连接方式(β-O-4、α-O-4、4-O-5、β-1、α-1、5-5)的63个木质素模化物的醚键(C-O)和C-C键的键离解能E_B进行了理论计算研究。分析了不同取代基对键离解能的影响以及键长与键离解能的相关性。计算结果表明,C-O键的键离解能通常比C-C键的小,在各种醚键中C_α-O键的平均键离解能最小,为182.7 kJ/mol;其次是β-O-4连接中的C_β-O键,苯环和烷烃基上的取代基对醚键的键离解能有较强的弱化作用,C-O键的键长和键离解能的相关性较差。与C-O键相比,C-C键的键离解能受苯环上取代基的影响很小,而烷烃基上的取代基对C-C键的键离解能有较大的影响,C-C键的键离解能和键长之间存在较强的线性关系,C-C键的键长越长,其键离解能越小。     

TiCl, TiH, and TiH+ bond energies: a test of a correlation-consistent Ti basis set

Correlation-consistent basis sets are developed for the Ti atom. The polarization functions are optimized for the average of the ³F and ⁵F states. One series of correlation-consistent basis sets is for 3d and 4s correlation, while the second series includes 3s and 3p correlation as well as 3d and 4s correlation. These basis sets are tested using the Ti ³F–⁵F separation and the dissociation energies of TiCl X⁴Φ, TiH X⁴Φ, and TiH⁺ X³Φ. The CCSD(T) complete basis set limit values are determined by extrapolation. The Douglas–Kroll approach is used to compute the scalar relativistic effect. Spin-orbit effects are taken from experiment and/or are computed at the CASSCF level. The Ti³F–⁵F separation is in excellent agreement with experiment, while the TiCl, TiH, and TiH⁺ bond energies are in good agreement with experiment. Extrapolation with the valence basis set is consistent with other atoms, while including 3s and 3p correlation appears to make extrapolation more difficult. Received: 20 January 1999 / Accepted: 26 February 1999 / Published online: 7 June 1999     

Effects of geminal disubstitution on C-H and N-H bond dissociation energies

Composite ab initio methods including G3, CBS-Q, and G3B3 were used to calculate the C-H and N-H bond dissociation energies (BDEs) of a variety of disubstituted methane and ammonia molecules. The calculated BDEs were in excellent agreement with the available experimental data. Using these reliable BDEs we studied the effects of geminal disubstitution on C-H and N-H BDEs. It was found that the effects of the two substituents were not additive. Detailed separation of the substituent effects on BDEs to those associated with the parent molecules and those associated with the radicals was then performed using appropriate isodesmic reactions. It was found the geminal substitution effects on the stabilities of methanes, methyl radicals, amines, and amine radicals were all governed by five basic types of energetic effects, namely, hyperconjugation effect (stabilizing), electrostatic attraction (stabilizing) or repulsion (destabilizing), conjugation saturation effect (destabilizing), captodative effect (stabilizing), and steric effect (destabilizing). The conformations of the species played an essential role in determining whether a particular energetic effect could take place. Because the carbon-centered and nitrogen-centered species often had quite different conformational preferences, the geminal substitution effects on these two classes of species were quite dissimilar to each other.     

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory

The C? NO₂ bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C? NO₂ bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO₂ groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol^?1 from experimental ones for CH₂(NO₂)₂ and CH(NO₂)₃, when the diffusion functions are not augmented. For the C(NO₂)₄ molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Micro-hydration of the MgNO3+ cation in the gas phase.

Coordination complexes of the magnesium nitrate cation with water [MgNO(3)(H(2)O)(n)](+) up to n=7 are investigated by experiment and theory. The fragmentation patterns of [MgNO(3)(H(2)O)(n)](+) clusters generated via electrospray ionization indicate a considerable change in stability between n=3 and 4. Further, ion-molecule reactions of mass-selected [MgNO(3)(H(2)O)(n)](+) cations with D(2)O reveal the occurrence of consecutive replacement of water ligands by heavy water, and in this respect the complexes with n=4 and 5 are somewhat more reactive than their smaller homologs with n=1-3 as well as the larger clusters with n=6 and 7. For the latter two ions, the theory suggests the existence of isomers, such as complexes with monodentate nitrato ligands as well as solvent-separated ion pairs with a common solvation shell. The reactions observed and the ion thermochemistry are discussed in the context of ab initio calculations, which also reveal the structures of the various hydrated cation complexes.     

碱金属离子对甘氨酸五肽气相解离过程的影响

为了获得更多的多肽结构信息,采用结构简单的甘氨酸五肽(简写为GGGGG或G5)作为模型,研究了碱金属离子(Li+、Na+、K+、Rb+)对甘氨酸五肽GGGGG气相解离过程的影响.将一定化学计量比的甘氨酸五肽分别和四种碱金属盐溶液混合后,静置10h,使反应达到平衡.电喷雾质谱结果表明,四种碱金属离子均可以在溶液中与甘氨酸五肽形成非共价复合物,其中主要组分为碱金属离子与G5配合比为1:1和2:1的非共价复合物.质谱碰撞诱导解离(CID)时的碰撞能量为25eV.气相碰撞诱导解离实验结果表明,在配合比为1:1的复合物中,其碎片化程度按照Li+、Na+、K+、Rb+的次序依次减小,Rb+的复合物碎裂过程中生成了不常见的c、z离子;在配合比为2:1的复合物中,其碎片化程度按照Li+、Na+、K+、Rb+的次序依次增大.与1:1的非共价复合物相比,Na+、K+、Rb+的2:1复合物的气相解离显得更加容易.除Li+外,两个碱金属离子对G5的活化能力明显较单个碱金属离子强,它们可以诱导多肽在更多位点断裂,生成更多类型的碎片离子.     

Theoretical studies of bond dissociation energies for removal of the nitrile group in some nitrile compounds

The CCN bond distances and bond dissociation energies (BDEs) are estimated by utilizing quantum chemical calculations for 16 nitrile compounds. Since DFT methods have been researched to have low basis sets sensitivity for small and medium molecules in our earlier work [Jun Zhao, Xinlu Cheng, Xiangdong. Yang, J. Mol. Struct. (Theochem) 766 (2006) 87] 16 nitrile compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) and the complete basis set (CBS-Q) method in conjunction with the 6-311G^** basis set. The obtained results are compared with the available experimental data. It is demonstrated that CBS-Q method, which can produce reasonable BDEs for some systems, seems unable to predict accurate BDEs here. While, the B3P86 calculated results agree very well with the experimental values. So B3P86 method is suitable for computing the reliable BDEs of CCN bond for nitrile compounds.     

Heterolytic and homolytic C-D bond dissociation energies of NADH models in acetonitrile and primary isotopic effects on hydride versus hydrogen atom transfer reactions

Heterolytic and homolytic C D bond dissociation energies of three NADH models: BNAH-4,4-d 2 , HEH-4,4-d 2 and AcrD 2 in acetonitrile were first estimated by using an efficient method. The results showed that the heterolytic C D bond dissociation energies are 65.2, 70.2, and 81.9 kcal/mol and the homolytic C D bond dissociation energies are 72.66, 70.69, and 74.95 kcal/mol for BNAH-4,4-d 2 , HEH-4,4-d 2 , and AcrD 2 , respectively. According to the bond dissociation energy differences of isotope isomers, an interesting conclusion can be made that the primary kinetic isotope effects are dependent not only on the zero-point energy difference of the isotope isomers, but also on the types of C D bond dissociations, and the C D bond homolytic dissociations should have much larger primary kinetic isotope effects (26.9 28.8) than the corresponding C D bond heterolytic dissociations (3.9-5.4).     

Simplification of electrospray mass spectra of Polysorbate 80 via cation transfer to carborane anions

Mass spectrometric analysis of polymer mixtures via electrospray ionization can be complicated due the presence of multiple ion types, multiple charge states and multiple oligomeric distributions that complicate the detection and identification of mixture components. Polysorbate 80 (commercially known as Tween^® 80) provides an example of this type, where the presence of polyoxyethylene sorbitan monooleate (PSO) byproducts gives rise to overlapping polymer distributions. It is desirable to simplify the spectrum in order to identify each component of what is inherently a complex mixture of fatty esters bound to different head groups. In this work, we show that gas‐phase ion/ion reactions with carborane anions allow for the charge reduction of Tween^® 80 peaks by selectively removing metal adducts bound to the synthetic polymer. The resulting singly charged spectrum reduces overlapping distributions and thus simplifies the identification of the components found in a Tween^® 80 sample. The overall approach described here would likely lead to similar benefits in the analysis of other polymers that tend to ionize via metal ion adduction. Copyright © 2016 John Wiley & Sons, Ltd.