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Kinetics and Mechanism of the Anilinolysis of Dipropyl Chlorophosphate in Acetonitrile
Ehtesham Ul Hoque,이해황 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.6
The kinetic studies on the reactions of dipropyl chlorophosphate (3O) with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) have been carried out in acetonitrile at 55.0 oC. The obtained deuterium kinetic isotope effects (DKIEs; kH/kD) are primary normal (kH/kD = 1.09-1.01) with the strongly basic anilines while secondary inverse (kH/kD = 0.74-0.82) with the weakly basic anilines. The steric effects of the two ligands on the rates are extensively discussed for the anilinolyses of the (R1O)(R2O)P(=O or S)Cl-type chlorophosphates and chlorothiophosphates. A concerted mechanism is proposed with a frontside nucleophilic attack involving a hydrogen-bonded four-center-type transition state for the strongly basic anilines and with a backside attack transition state for the weakly basic anilines on the basis of the DKIEs, primary normal and secondary inverse with the strongly and weakly basic anilines, respectively.
Kinetics and Mechanism of the Anilinolysis of Dibutyl Chlorophosphate in Acetonitrile
Ehtesham Ul Hoque,이해황 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.2
The nucleophilic substitution reactions of dibutyl chlorophosphate (3) with substituted anilines (XC6H4NH2)and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at 55.0 oC. The obtained deuterium kinetic isotope effects (DKIEs; kH/kD) are secondary inverse (kH/kD = 0.86-0.97) with the strongly basic anilines while primary normal (kH/kD = 1.04-1.10) with the weakly basic anilines. The DKIEs, steric effects of the two ligands, activation parameters, cross-interaction constants, variation trends of the kH/kD values with X, and mechanism are discussed for the anilinolyses of the nine (R1O)(R2O)P(=O)Cl-type chlorophosphates. A concerted mechanism is proposed with a backside nucleophilic attack transition state for the strongly basic anilines and with a frontside attack involving a hydrogen-bonded four-center-type transition state for the weakly basic anilines on the basis of the magnitudes, secondary inverse and primary normal, and variation trends of the kH/kD values with X.
Kinetics and Mechanism of the Pyridinolysis of Diisopropyl Chlorothiophosphate in Acetonitrile
Ehtesham Ul Hoque,이해황 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.10
The nucleophilic substitution reactions of diisopropyl chlorothiophosphate (5) with X-pyridines have been kinetically studied in MeCN at 35.0 oC. The Hammett and Brönsted plots for the substituent X variations in the nucleophiles show biphasic concave upwards with a break point at X = 3-Ph. The pyridinolysis rate of 5 exhibits great negative deviation from the Taft plot. A concerted SN2 mechanism is proposed involving a change of the attacking direction of the X-pyridines from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines.
Ehtesham Mustafa Qureshi,Xing Shen,JinJin Chen 한국항공우주학회 2014 International Journal of Aeronautical and Space Sc Vol.15 No.4
Synchronized switch damping (SSD) techniques have recently been developed for structural vibration control using piezoelectric materials. In these techniques, piezoelectric materials are bonded on the vibrating structure and shunted by a network of electrical elements. These piezoelectric materials are switched according to the amplitude of the excitation force to damp vibration. This paper presents a new SSD technique called ‘synchronized switch damping on negative capacitance and adaptive voltage sources’ (SSDNCAV). The technique combines the phenomenon of capacitance transient charging and electrical resonance to effectively dampen the structural vibration. Also, the problem of stability observed in the previous SSD techniques is effectively addressed by adapting the voltage on the piezoelectric patch according to the vibration amplitude of the structure. Analytical expressions of vibration attenuation at the resonance frequency are derived, and the effectiveness of this new technique is demonstrated, for the control of a resonant cantilever beam with bonded piezoelectric patches, by comparing with SSDI, SSDVenh, and SSDNC techniques. Theoretical predictions and experimental results show the remarkable vibration damping capability of SSDNCAV technique, which was better than the previous SSD techniques. The broadband vibration control capabilities of SSDNCAV technique are also demonstrated, which exceed those of previous SSD techniques.
Ehtesham Mustafa Qureshi,Xing Shen,Lulu Chang 한국항공우주학회 2016 International Journal of Aeronautical and Space Sc Vol.17 No.4
Synchronized switch damping (SSD) is a structural vibration control technique in which a piezoelectric patch attached to or embedded into the structure is connected to or disconnected from the shunt circuit in order to dissipate the vibration energy of the host structure. The switching process is performed by a digital signal processor (DSP) which detects the displacement extrema and generates a command to operate the switch in synchronous with the structure motion. Recently, autonomous SSD techniques have emerged in which the work of DSP is taken up by a low pass filter, thus making the whole system autonomous or self-powered. The control performance of the previous autonomous SSD techniques heavily relied on the electrical quality factor of the shunt circuit which limited their damping performance. Thus in order to reduce the influence of the electrical quality factor on the damping performance, a new autonomous SSD technique is proposed in this paper in which a negative capacitor is used along with the inductor in the shunt circuit. Only a negative capacitor could also be used instead of inductor but it caused saturation of negative capacitor in the absence of an inductor due to high current generated during the switching process. The presence of inductor in the shunt circuit of negative capacitor limits the amount of current supplied by the negative capacitance, thus improving the damping performance. In order to judge the control performance of proposed autonomous SSDNCI, a comparison is made between the autonomous SSDI, autonomous SSDNC and autonomous SSDNCI techniques for the control of an aluminum cantilever beam subjected to both single mode and multimode excitation. A value of negative capacitance slightly greater than the piezoelectric patch capacitance gave the optimum damping results. Experiment results confirmed the effectiveness of the proposed autonomous SSDNCI technique as compared to the previous techniques. Some limitations and drawbacks of the proposed technique are also discussed.