High Bond Dissociation Energy Research Articles

Gallium Halides as Alternative Ligands to CO and N2 in Transition Metal Complexes: A Bonding Analysis

Quantum chemical calculations using gradient-corrected DFT at the BP86/TZ2P+ level have been carried out for the gallium halide complexes [Fe(CO)4(GaX)] (X = F−I) and for [Fe(CO)5] and [Fe(CO)]4(N2)]. The nature of the metal−ligand bond has been investigated with an energy decomposition analysis. The Fe−GaX bonds in [Fe(CO)4(GaX)] have rather high bond dissociation energies that are smaller than the BDE of [Fe(CO)5] but larger than the BDE of [Fe(CO)]4(N2)]. The axial isomer of [Fe(CO)4(GaF)] is predicted to be slightly more stable than the equatorial form, while the equatorial isomers of the heavier halogen systems [Fe(CO)4(GaX)] (X = Cl−I) are a bit lower in energy than the axial form. The energy difference between the two isomers is for all gallium complexes [Fe(CO)4(GaX)] smaller than 1.0 kcal/mol. The ratio of covalent bonding and electrostatic attraction in the (CO)4Fe−GaX bonds is very similar to the values that are calculated for the (CO)4Fe−CO and (CO)4Fe−N2 bonds. The analysis of the bonding sit...

Formation of Methyl Acrylate from CO2 and Ethylene via Methylation of Nickelalactones

The nickel-induced coupling of ethylene and CO2 represents a promising pathway toward acrylates. To overcome the high bond dissociation energies of the M−O moieties, we worked out an in situ methylation of nickelalactones to realize the β-hydride elimination and the liberation of the acrylate species.

Autoxidation Resistant Cyclopentyl Methyl Ether

Abstract The bond dissociation energy of the C–H bond at the α-position of an ether oxygen in cyclopentyl methyl ether (CPME) has been evaluated theoretically to be 393.3 kJ/mol by using an isodesmic reaction method. Essential factors accounting for this rather higher bond dissociation energy in CPME comparable to secondary C–H bond have been investigated on the basis of the structures and their thermodynamic data such as heats of formation (ΔHf°) of CPME radical and relevant ether radicals evaluated by the theoretical approach.

Structures and Properties of s-Triazine Derivations Substituted by Substitutent Groups Containing Nitrogen

B3LYP/aug-cc-pvDZ level of theory was applied to study the geometries, bond dissociation energies,and energetic material properties of s-triazine derivatives in which hydrogen atoms of s-triazine have been substituted by —CN, —NO2, —NH2, —N3, —N2H, —NHNH2, —N4H, and —N4H3 groups. Compared with the parent molecules unsubstituted, derivatives substituted by —CN and —NH2 groups result in higher bond dissociation energies, whereas the others lead to lower ones. The studies indicated that the higher formation heats of compounds substituent groups possess, the higher ones of derivatives. The normalized formation heats of these derivatives substituted by —CN, —N3, and —N4H are 71.9, 78.7, and 82.6 kJ, which are higher than that of triazido-s-triazine (70.2 kJ) reported. For derivatives substituted by —N4H, —N3, —N4H3, —N2H, and —CN groups, formation heats calculated lie in the range of 863.1-1735.2 kJ·mol-1, but derivatives substituted by —N4H and —N4H3 show low dissociation energies and relatively low stability.

THERMOGRAVIMETRIC ANALYSIS AND THERMAL AGEING OF CROSSLINKED NITRILE RUBBER/POLY- (ETHYLENE-CO-VINYL ACETATE) BLENDS

The thermal behaviour of nitrile rubber (NBR)/poly(ethylene-co-vinyl acetate) (EVA) blends was studied by thermogravimetry. The effects of blend ratio, different crosslinking systems (sulphur, peroxide and mixed), various fillers (silica, clay and carbon black) and filler loading on the thermal properties were evaluated. It was found that the initial decomposition temperature increased with the addition of NBR to EVA. Among the various crosslinking systems studied, the peroxide cured system showed the highest initial decomposition temperature. This is associated with the high bond dissociation energy of C–C linkages. The addition of fillers improved the thermal stability of the blend. The mass loss at different temperatures and activation energy of degradation were also studied. The thermal ageing of these blends was carried out at 50 and 100°C for 72 h. It was seen that the properties are not affected by the mild ageing condition. Also, the peroxide cured system was found to exhibit better retention in properties, than other crosslinking systems.

Adducts and dimers of SF n+ ( n = 1–5) with benzene, acetonitrile, and pyridine. Gas-phase generation and ab initio structures and thermochemistry

Pentaquadrupole (QqQqQ) mass spectrometry is used to explore the abilities of gaseous SF n + ( n = 1–5) ions to form adducts and dimers with three π-electron rich molecules—benzene, acetonitrile, and pyridine, whereas ab initio calculations estimate most feasible structures, bond dissociation energies (BDEs), and reaction enthalpies of the observed products. With benzene, SF + reacts by net H-by-SF +· replacement. As suggested by the calculations, this novel benzene reaction forms ionized benzenesulfenyl fluoride, C 6H 5–SF +·, via a Wheland-type intermediate that spontaneously loses a H atom. SF 3 + forms a rare, loosely bonded π complex with benzene, [Bz ⋯ SF 3] +, which is stable toward both H and HF loss. No dimer, Bz 2SF 3 +, is formed. According to calculations, an unsymmetrically bonded, π-coordinated Bz 2SF 3 + dimer exists, i.e. (Bz–SF 3 ⋯ Bz) +, but its formation from [Bz ⋯ SF 3] + is endothermic; hence, thermodynamically unfavorable. With acetonitrile, SF 2 +·, SF 3 +, and SF 5 + form both adducts and dimers. CH 3–C ·N–SF 2 + (a new distonic ion) and CH 3CN–SF 5 + are covalently bonded, but CH 3CN ⋯ SF 3 + is loosely bonded. The binding natures of the acetonitrile adducts are reflected in the dimers; [CH 3CN–SF 2 ⋯ NCCH 3] +· and [CH 3CN–SF 5 ⋯ NCCH 3] + are unsymmetrically bonded, whereas [CH 3CN ⋯ SF 3 ⋯ NCCH 3] + is symmetrically and loosely bonded. Such dimers as [CH 3CN ⋯ SF 3 ⋯ NCCH 3] + are ideal for measurements of ion affinity via the Cooks’ kinetic method. With pyridine, only SF 3 + forms adduct and dimer. Py–SF 3 + is covalently bonded through nitrogen; [Py ⋯ SF 3 ⋯ Py] + is loosely but unsymmetrically bonded. The unsymmetric 2.28 and 2.44 Å long N–S bonds in [Py ⋯ SF 3 ⋯ Py] +, which are expected to rapidly interconvert, result likely from steric hindrance that forces orthogonal alignment of the two pyridine rings. Most observed adducts and dimers display relatively high BDEs, i.e. they are formed in thermodynamically favorable reactions. The extents of dissociation of the adducts and dimers observed in MS 3 experiments reflect the structures and BDEs predicted by the calculations.

How Long Can You Make an Oxygen Chain?

This paper reports theoretical gas-phase structures and energetics using G2(MP2) theory for saturated oxygen chains of the general formula HOnH. Structural trends are discussed using a simple hyperconjugation model which is capable of giving a qualitative explanation for trends in bond lengths and dihedral angles. Bond dissociation energies (BDEs) are calculated for chains of increasing length, giving 49.9, 33.9, and 17.8 kcal/mol for H2O2, H2O3, and H2O4, respectively. From an analysis of the radical stabilization energy of the fragments remaining after dissociation, it is shown that a minimum value for the BDE for any hydrogen polyoxide is 6.4 kcal/mol, which occurs for the center bond in H2O6, and that longer chains will have a higher BDE. Decomposition pathways responsible for the observed instability of the polyoxides higher than hydrogen peroxide are discussed and results are given for three low-barrier dissociation paths: a solvent-assisted path, a base-catalyzed path, and a proton relay mechanism. These mechanisms are probably general and account for the instability of polyoxide chains in proton-containing solvents. Preventing proton transfer, e.g. by perfluoroalkylation, would therefore be expected to increase chain stability, in agreement with experimental observations.

Donor-acceptor effects on the stability of radicals derived from .alpha.-dialkylamino ketones

The bond dissociation energies (BDEs) for the acidic C−H bonds in CH 3 COCH 2 NMeNMe 2 and CH 3 COCH 2 NEt 2 ketones, estimated in DMSO from pK HA and oxidation potential data, are 3-4 kcal/mol higher than that for the acidic C−H bond in PhCOCH 2 NMe 2 . It is suggested that the electronic and steric effects of the Ph group dictate a Z structure for the precursor enolate ion and the generation of a radical that is strongly stabilized by electrostatic effects, which are responsible for the apparent synergistic effects of the PhCO and NMe 2 groups in stabilizing the PhCOCHNMe 2 radical. This suggestion was supported by the observation that the BDEs of the acidic C−H bonds in ketocyclic analogues of the α-dialkylamino open-chain ketones, wherein the enolate ion is locked in an E structure, have higher BDEs by 9-11.5 kcal/mol