A comprehensive study focused on the preparation of disubstituted carboxonium derivatives of
-decaborate anion 2,6-B
H
O
CC
H
was carried out. The proposed synthesis of the target product was based ...on the interaction between the anion B
H
and benzoic acid C
H
COOH. It was shown that the formation of this product proceeds stepwise through the formation of a mono-substituted product B
H
OC(OH)C
H
. In addition, an alternative one-step approach for obtaining the target derivative is postulated. The structure of tetrabutylammonium salts of carboxonium derivative ((C
H
)
N)2,6-B
H
O
CC
H
was established with the help of X-ray structure analysis. The reaction pathway for the formation of 2,6-B
H
O
CC
H
was investigated with the help of density functional theory (DFT) calculations. This process has an electrophile induced nucleophilic substitution (EINS) mechanism, and intermediate anionic species play a key role. Such intermediates have a structure in which one boron atom coordinates two hydrogen atoms. The regioselectivity for the process of formation for the 2,6-isomer was also proved by theoretical calculations. Generally, in the experimental part, the simple and available approach for producing disubstituted carboxonium derivative was introduced, and the mechanism of this process was investigated with the help of theoretical calculations. The proposed approach can be applicable for the preparation of a wide range of disubstituted derivatives of
-borate anions.
The process of protonation of 2,6-B
H
O
CCH
was investigated both theoretically and experimentally. The most suitable conditions for protonation of the derivative 2,6-B
H
O
CCH
were found. The ...process of protonation was carried out in the presence of an excess of trifluoromethanesulfonic acid CF
SO
H at room temperature in dichloromethane solution. The structure of the resulting complex 2,6-B
H
O
CCH
*H
was established using NMR data and the results of DFT calculations. An additional proton atom H
was found to be localized on one of the facets that was opposite the boron atom in a substituted position, and which bonded mainly with one apical boron atom. The main descriptors of the B-H
bond were established theoretically using QTAIM and NBO approaches. In addition, the mechanism of 2,6-B
H
O
CCH
protonation was investigated.
In the present work, a convenient and straightforward approach to the preparation of borylated amidines based on the
-dodecaborate anion B
H
NCCH
NHR-, R=H, Alk, Ar was developed. This method has two ...stages. A nitrile derivative of the general form B
H
NCCH
was obtained, using a modified technique, in the first stage. On the second stage the resulting molecular system interacted with primary amines to form the target amidine products. This approach is characterised by a simple chemical apparatus, mild conditions and high yields of the final products. The mechanism of the addition of amine to the nitrile derivative of the
-dodecaborate anion was studied, using quantum-chemical methods. The interaction between NH
and B
H
NCCH
ammonia was chosen as an example. It was found that the structure of the transition state determines the stereo-selectivity of the process. A study of the biological properties of borylated amidine sodium salts indicated that the substances had low toxicity and could accumulate in cancer cells in significant amounts.
The preparation of novel nitrilium derivatives of closo-dodecaborate anion B12H11NCR−, R = n-C3H7, i-C3H7, 4-C6H4CH3, 1-C10H7 is described. Target compounds were obtained in good yields (up to 73%). ...The synthesis of target borylated nitrilium derivatives was characterised by the simplicity of the chemical apparatus and the absence of the necessity for the purification of desired compounds. The crystal structures of previously obtained B12H11NCCH3− and novel B12H11NCC3H7− were established with the help of X-ray structure analysis. DFT-analysis of several nitrilium derivatives B12H11NCR−, R = CH3, C3H7, 4-CH3C6H4 was carried out. The main peculiarities of the C≡N bond of the exo-polyhedral substituent were revealed in terms of bond lengths, bond orders and atomic charges. The LUMO orbitals of the systems considered were examined for understanding of the electrophilic nature of the nitrilium derivatives of the closo-dodecaborate anion.
By reacting nitrilium derivative of the closo-dodecaborate anion, Bu4NB12H11N≡CR (where R = Me, Et, nPr, iPr, p-tolyl), with lithium aluminum hydride (LiAlH4), N-alkylammonium derivatives of the ...closo-dodecaborate anion, and Bu4NB12H11NH2CH2R, were obtained. The reduction reaction procedure was optimized, achieving yields close to quantitative (90–95%). The structure of the compound Bu4NB12H11NH2CH2CH3 was determined using X-ray structural analysis. It was found that substituting lithium aluminum hydride (LiAlH4) with sodium borohydride (NaBH4) leads to the same products but only upon heating, while the reaction with LiAlH4 proceeds at room temperature.
The use of 3-D simulation programs and in particular NX and ANSYS simulators brought the design and fine tuning of gas turbine engine combustion chambers to the next level, as it allows improving the ...performance (increased combustion efficiency, reduced radial and circumferential non-uniformity of the total gas temperature), as well as determining the weak points of the structure. The article analyzes the flow of fuel jets from the finger sprayers of the afterburner of the combustion chamber of a gas turbine engine. The problem of optimizing the distribution of fuel is formulated: the fuel at the exit of the flame tube is to be evenly distributed by varying the diameters of the holes in the fuel manifolds. Restrictions are imposed on the optimization problem the supply of fuel to the peripheral zone at the outlet of the afterburner is reduced by a factor of five. The optimization effect is verified by comparing the fuel combustion efficiency in the case of standard fuel distribution with the optimized distribution option using the NX and ANSYS 3-D simulations. As a result, we observe an increase in combustion efficiency in all afterburner modes of engine operation.
We have performed a novel comparison between electron-beam polarimeters based on Møller and Compton scattering. A sequence of electron-beam polarization measurements were performed at low beam ...currents (<5 μA) during the Qweak experiment in Hall-C at Jefferson Lab. These low current measurements were bracketed by the regular high current (180 μA) operation of the Compton polarimeter. All measurements were found to be consistent within experimental uncertainties of 1% or less, demonstrating that electron polarization does not depend significantly on the beam current. This result lends confidence to the common practice of applying Møller measurements made at low beam currents to physics experiments performed at higher beam currents. The agreement between two polarimetry techniques based on independent physical processes sets an important benchmark for future precision asymmetry measurements that require sub-1% precision in polarimetry.
We report on the highest precision yet achieved in the measurement of the polarization of a low-energy, O(1GeV) , continuous-wave (CW) electron beam, accomplished using a new polarimeter based on ...electron-photon scattering, in Hall C at Jefferson Lab. A number of technical innovations were necessary, including a novel method for precise control of the laser polarization in a cavity and a novel diamond microstrip detector that was able to capture most of the spectrum of scattered electrons. The data analysis technique exploited track finding, the high granularity of the detector, and its large acceptance. The polarization of the 180−μA , 1.16-GeV electron beam was measured with a statistical precision of <1% per hour and a systematic uncertainty of 0.59%. This exceeds the level of precision required by the Qweak experiment, a measurement of the weak vector charge of the proton. Proposed future low-energy experiments require polarization uncertainty <0.4% , and this result represents an important demonstration of that possibility. This measurement is the first use of diamond detectors for particle tracking in an experiment. It demonstrates the stable operation of a diamond-based tracking detector in a high radiation environment, for two years.
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The addition of amino acid esters to 2-B10H9–NCMe− Bu4N+ salt under mild conditions affords amidine closo-decaborates in high yields. The structure of compound ...(PPh4)2-B10H9NH=C(Me)NHCH2COOEt was elucidated by single-crystal XRD analysis.
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