Hydrazines computational studies

A recent paper by Singh et al. summarized the mechanism of the pyrazole formation via the Knorr reaction between diketones and monosubstituted hydrazines. The diketone is in equilibrium with its enolate forms 28a and 28b and NMR studies have shown the carbonyl group to react faster than its enolate forms.Computational studies were done to show that the product distribution ratio depended on the rates of dehydration of the 3,5-dihydroxy pyrazolidine intermediates of the two isomeric pathways for an unsymmetrical diketone 28. The affect of the hydrazine substituent R on the dehydration of the dihydroxy intermediates 19 and 22 was studied using semi-empirical calculations. ... 

The preparation, structural characterization, and computational studies of several 1,2,4-diazaphospholes have recently been reported <2007T9129, 2007EJI3491>. 177-3,5-Diphenyl-l,2,4-diazaphosphole 137 was prepared by the reaction of l,3-bis(dimethylamino)-2-phosphaallyl chloride 136 and hydrazine in chloroform in good yield (Equation 16) <2007T9129>. The structure of compound 137 was established by X-ray diffraction, and the geometry of this product and several other 1,2,4-diazaphospholes was rationalized by DFT calculations at the B3LYP/6-311++G(d,p) level <2007T9129>. 

The reaction transformation should start by reacting malonic ester and hydrazine to prepare cyclic malonic hydrazide. It is well known that thionyl chloride can transfer amides to vinyl chloride, but in our case we used the pyrazole tautomer. We believe that this tautomer must be a sufficiently reactive diene for a Diels-Alder cycloaddition reaction because of the findings of one experimental study performed by Adam and coworkers [62] and one computational study presented above. There are at least two key factors that must be addressed before this reaction scheme can be considered seriously the likelihood that 3,5-dichloro-[4//]-pyrazole will participate in a cycloaddition reaction and the stability of the formed cycloadduct. One can also question the stability and the availability of cyclic hydrazides of malonic ester. These compounds are unstable but they can... 

Pre-steady-state stopped-flow and rapid quench techniques applied to Mo nitrogenase have provided powerful approaches to the study of this complex enzyme. These studies of Klebsiella pneumoniae Mo nitrogenase showed that a pre-steady-state burst in ATP hydrolysis accompanied electron transfer from the Fe protein to the MoFe protein, and that during the reduction of N2 an enzyme-bound dinitrogen hydride was formed, which under denaturing conditions could be trapped as hydrazine. A comprehensive model developed from a computer simulation of the kinetics of these reactions and the kinetics of the pre-steady-state rates of product formation (H2, NH3) led to the formulation of Scheme 1, the Thorneley and Lowe scheme (50) for nitrogenase function. 

A theoretical study using the density functional theory (DFT) method has been performed to rationalize the mechanism of the reactions between 1,3-dialkynes and hydroxylamine or hydrazine for the formation of 3,5-disubstituted isoxazoles or pyrazoles, respectively The computational results support a bimolecular proton transfer as the rate-determining step providing valuable clues for the use of Bronsted acid/base catalysts to promote the cyclization reaction (14OBC7503). 

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