The structure, thermochemical properties and reaction pathways of a cyclic amine diborane complex (1,3-bis(λ
4
-boraneyl)-1λ
4
,3λ
4
-imidazolidine) were investigated using quantum chemical ...calculations. Structural and thermochemical analysis revealed that the simultaneous and spontaneous elimination of both hydrogen molecules from this complex is predicted to occur under thermoneutral conditions. This observation is further supported by the investigation of the BH
3
-catalysed dehydrogenation pathway. The calculated thermochemical parameters indicate that the energy requirements for hydrogen release from this complex are minimal, suggesting efficient hydrogen release capability under suitable conditions. Additionally, the activation barriers, ∼75 and ∼20 kJ mol
−1
for the first and second dihydrogen release from the catalysed dehydrogenation reactions of this compound exhibit moderate kinetics, confirmed by kinetic studies. These findings and the ability of the system to easily release two molecules of dihydrogen emphasize the potential of 1,3-bis(λ
4
-boraneyl)-1λ
4
,3λ
4
-imidazolidine as a highly effective hydrogen storage material.
The structure, thermochemical properties and reaction pathways of a cyclic amine diborane complex (1,3-bis(λ
4
-boraneyl)-1λ
4
,3λ
4
-imidazolidine) were investigated using quantum chemical calculations.
The structure, thermochemical properties and reaction pathways of a cyclic amine diborane complex (1,3-bis(λ
-boraneyl)-1λ
,3λ
-imidazolidine) were investigated using quantum chemical calculations. ...Structural and thermochemical analysis revealed that the simultaneous and spontaneous elimination of both hydrogen molecules from this complex is predicted to occur under thermoneutral conditions. This observation is further supported by the investigation of the BH
-catalysed dehydrogenation pathway. The calculated thermochemical parameters indicate that the energy requirements for hydrogen release from this complex are minimal, suggesting efficient hydrogen release capability under suitable conditions. Additionally, the activation barriers, ∼75 and ∼20 kJ mol
for the first and second dihydrogen release from the catalysed dehydrogenation reactions of this compound exhibit moderate kinetics, confirmed by kinetic studies. These findings and the ability of the system to easily release two molecules of dihydrogen emphasize the potential of 1,3-bis(λ
-boraneyl)-1λ
,3λ
-imidazolidine as a highly effective hydrogen storage material.
The structure, thermochemical properties and reaction pathways of a cyclic amine diborane complex (1,3-bis(λ4-boraneyl)-1λ4,3λ4-imidazolidine) were investigated using quantum chemical calculations. ...Structural and thermochemical analysis revealed that the simultaneous and spontaneous elimination of both hydrogen molecules from this complex is predicted to occur under thermoneutral conditions. This observation is further supported by the investigation of the BH3-catalysed dehydrogenation pathway. The calculated thermochemical parameters indicate that the energy requirements for hydrogen release from this complex are minimal, suggesting efficient hydrogen release capability under suitable conditions. Additionally, the activation barriers, ∼75 and ∼20 kJ mol−1 for the first and second dihydrogen release from the catalysed dehydrogenation reactions of this compound exhibit moderate kinetics, confirmed by kinetic studies. These findings and the ability of the system to easily release two molecules of dihydrogen emphasize the potential of 1,3-bis(λ4-boraneyl)-1λ4,3λ4-imidazolidine as a highly effective hydrogen storage material.
Diketene (4-methylideneoxetan-2-one) is a precursor to the formation of either two molecules of ketene, or allene and CO
2
using pyrolysis techniques. It is not known experimentally which of these ...pathways is followed, or indeed if both are, during the dissociation process. We use computational methods to show that the formation of ketene has a lower barrier than formation of allene and CO
2
under standard conditions (by 12 kJ/mol). According to CCSD(T)/CBS, CBS-QB3 and M06-2X/cc-pVTZ calculations the formation of allene and CO
2
is favoured thermodynamically under standard conditions of temperature and pressure; however, kinetically the formation of ketene is favoured from transition state theory calculations at standard and elevated temperatures.
Graphical abstract
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The gas-phase molecular structure of iso-propyl(
tert
-butyl)(trichlorosilyl)phosphine has been determined using a combination of gas electron diffraction and computational methods. The structure ...presents a conformational challenge that required use of the SARACEN method to combine theoretical observations into the least-squares refinement process, a great advance on the techniques used to solve the structure of the parent trisilyl phosphine. Five conformers were found on the potential-energy surface for iso-propyl(
tert
-butyl)(trichlorosilyl)phosphine using the UCONGA program, and following a series of individual structure refinements a combined model with the two most abundant confirmers was evaluated. Key structural parameters (
r
a
) include
r
P-Si 225.5(6) pm,
r
Si-Cl
mean
204.0(1) pm and
r
P-C
mean
204.0(1) pm, ∠P-C-H 101.5(5)°, ∠C-C-C (iPr) 110.5(5)°, ∠C-C-C (
t
Bu) 109.2(5)° and ∠C-P-C 105.4(5)°.
GED has evolved hugely in the 50 years of Dalton Transactions. Combining experimental and theoretical data now allows complicated structures free from intermolecular interactions like iso-propyl(
tert
-butyl)(trichlorosilyl)phosphine to be revealed.
The gas-phase molecular structure of ketene has been determined using samples generated by the pyrolysis of acetic anhydride (giving acetic acid and ketene), using one permutation of the ...very-high-temperature (VHT) inlet nozzle system designed and constructed for the gas electron diffraction (GED) apparatus based at the University of Canterbury. The gas-phase structures of acetic anhydride, acetic acid, and ketene are presented and compared to previous electron diffraction and microwave spectroscopy data to show improvements in data extraction and manipulation with current methods. Acetic anhydride was modeled with two conformers, rather than a complex dynamic model as in the previous study, to allow for inclusion of multiple pyrolysis products. The redetermined gas-phase structure of acetic anhydride (obtained using the structure analysis restrained by ab initio calculations for electron diffraction method) was compared to that from the original study, providing an improvement on the description of the low vibrational torsions compared to the dynamic model. Parameters for ketene and acetic acid (both generated by the pyrolysis of acetic anhydride) were also refined with higher accuracy than previously reported in GED studies, with structural parameter comparisons being made to prior experimental and theoretical studies.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Poly(2‐ethylhexyl acrylate) is synthesized by conventional radical bulk polymerization both with and without 1‐dodecane thiol as chain transfer agent (CTA) at temperatures from 4 to 140 °C. ...Electrospray‐ionization mass spectrometry is used to analyze the polymer. This reveals the occurrence of significant β‐scission at high temperature and confirms the presence of CTA‐capped polymers at all temperatures, as well as combination products from 4 to 65 °C. Subsequent 13C melt‐state NMR analysis allows quantification of branching and β‐scission. Both are reduced when CTA is present, consistent with a “patching” effect. As expected, the amounts of β‐scission and branching increase with synthesis temperature, although β‐scission dominates at the highest temperature. The backbiting rate coefficient of 2‐ethylhexyl acrylate is determined from NMR results, taking β‐scission into account for the first time. Remarkable agreement with literature kbb values is obtained, especially for activation energy. This strongly suggests family‐type behavior for acrylate kbb.
Poly(2‐ethylhexyl acrylate) is synthesized from 4 to 140 °C and characterized by electrospray‐ionization mass spectrometry and 13C melt‐state NMR spectroscopy. The percentages of branching points and unsaturated terminal double bonds are determined, and thus the backbiting rate coefficient is estimated.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In situ dehydrogenation of azetidine–BH3, which is a candidate for hydrogen storage, was observed with the parent and dehydrogenated analogue subjected to rigorous structural and thermochemical ...investigations. The structural analyses utilized gas electron diffraction supported by high-level quantum calculations, while the pathway for the unimolecular hydrogen release reaction in the absence and presence of BH3 as a bifunctional catalyst was predicted at the CBS-QB3 level. The catalyzed dehydrogenation pathway has a barrier lower than the predicted B–N bond dissociation energy, hence favoring the dehydrogenation process over the dissociation of the complex. The predicted enthalpy of dehydrogenation at the CCSD(T)/CBS level indicates that mild reaction conditions would be required for hydrogen release and that the compound is closer to thermoneutral than linear amine boranes. The entropy and free energy change for the dehydrogenation process show that the reaction is exergonic, energetically feasible, and will proceed spontaneously toward hydrogen release, all of which are important factors for hydrogen storage.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Display omitted
•UCONGA is a new open-source program for generating and analysis all possible sterically-allowed conformers of molecules.•The conformational search algorithm does not require any ...force field or user-adjustable parameters.•A divide-and-conquer approach makes it possible to generate conformer ensembles for large, flexible molecules.•Conformer ensembles are analysed by clustering and using heatmaps; based on differences between conformer sizes, torsion angles and atomic positions.
Molecular properties depend on molecular structure, so the first step in any computational chemistry investigation is to generate all thermally accessible conformers. Typically it is necessary to make a trade-off between the number of conformers to be explored and the accuracy of the method used to calculate their energies. Ab initio potential energy surface scans can, in principle, be applied to any molecule, but their conformational cost scales poorly with both molecular size and dimensionality of the search space. Specialized conformer generation techniques rely on parameterized force fields and may also use knowledge-based rules for generating conformers, and are typically only available for drug-like organic molecules. Neither approach is well-suited to generating or identifying chemically sensible conformers for larger non-organic molecules. The Universal CONformer Generation and Analysis (UCONGA) program package fills this niche. It requires no parameters other than built-in atomic van der Waals radii to generate comprehensive ensembles of sterically-allowed conformers, for molecules of arbitrary composition and connectivity. Analysis scripts are provided to identify representative structures from clusters of similar conformers, which may be further refined by subsequent geometry optimization. This approach is particularly useful for molecules not described by parameterized force fields, as it minimizes the number of computationally intensive ab initio calculations required to characterize the conformer ensemble. We anticipate that UCONGA will be particularly useful for computational and structural chemists studying flexible non-drug-like molecules.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
10.
A diverse view of science to catalyse change Urbina-Blanco, César A; Jilani, Safia Z; Speight, Isaiah R ...
Chemical science (Cambridge),
09/2020, Volume:
11, Issue:
34
Journal Article
Peer reviewed
Open access
Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do. We can value diversity not only in words, but also in actions.
...Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do. We must value diversity not only in words, but also in actions.
Full text
Available for:
IJS, KILJ, NUK, UL, UM, UPUK
PDF
