ALBERT

Beschreibung: The electrochemical oxidation of benzyl and substituted benzyl alcohols including primary and secondary alcohols and piperonyl alcohol was carried out in an undivided cell using platinum electrodes in a biphasic medium using Cl − /OCl − as the redox mediator. In most cases, selective oxidation of alcohols to the corresponding aldehydes or ketones was achieved with high yields of products by the in situ generated chloronium ion. This method is simple and gives better yields of products compared with chemical methods of oxidation. Copyright © 2015 John Wiley & Sons, Ltd. R = Phenyl substituted phenyl, benzyl, naphthyl, furfuryl, piperonoyl, Ph-CH = CH-; R 1 = -H and alkyl.

Beschreibung: Acyl transfers are key reactions in biology and in the laboratory. In biological systems they are involved in energy transport, in the assembly of complex molecules and in the mechanisms of efficient action of many hydrolytic enzymes. We report a mechanistic and calculational study of the selective N -acylation reactions of amino acids by substituted aspirins, under mild conditions, in water at 25 °C. The acetylated amino-acid products of the reactions were identified by nuclear magnetic resonance, and the reaction steps were studied by density functional theory. Copyright © 2012 John Wiley & Sons, Ltd. We report a mechanistic and calculational study of the selective N-acylation reactions of amino acids by substituted aspirins, under mild conditions, in water at 25°C. The acetylated amino-acid products of the reactions were identified by NMR, and the reaction steps were studied by Density Functional Theory.

Beschreibung: The tautomerism of the aliphatic MeC(NH 2 )═NOH and the aromatic PhC(NH 2 )═NOH amidoximes in protic (H 2 O, MeOH) and aprotic (Me 2 CO, Me 2 SO, and CHCl 3 ) solvents was studied by density functional theory calculations at the M06-2X/6-311+G(d,p) level of theory. In both types of solutions, these species exist in 3 tautomeric forms, viz, ( Z )- or ( E )-amidoximes, and ( Z )-aminonitrone. The ( Z )-form is the dominant, and energy gap between the ( Z )- and ( E )-tautomers of the amidoximes slightly depends on the nature of a solvent and significantly higher than that for other oxime species. For the amidoximes, the zwitterionic ( Z )-aminonitrone form is stabilized by protic solvents. The oxime-nitrone energy gap is reduced by electron-donor substituents at the oxime moiety at different types of oxime species. The tautomerism of various amidoximes in protic and aprotic solvents was studied by DFT calculations at the M06-2X/6-311+G(d,p) level of theory. In both types of solutions, these species exist in 3 tautomeric forms, ie, ( Z )- or ( E )-amidoximes and ( Z )-aminonitrone, and the former form is the dominant. The oxime-nitrone energy gap is reduced by electron-donor substituents at the oxime moiety, and it is the lowest in the case of amidoximes due to strong + M effect of the NH 2 group.

Beschreibung: For the first time, one-pot solid-state synthesis of 12 photochromic materials based on photochromic dihydroindolizine system substituted in both fluorene part (region A) and the heterocyclic part (region C) has been established. This method has immense advantages, which are short-time reaction, high-yield and low-yield by-products, and easily purification and separation processes . In addition, this method will help in getting over the tremendously purification and low-yield problems faced since the worth-finding of this family of photochromic materials. The absorption maxima ( λ max ) and the half-lives ( t 1 / 2 ) of the colored betaines were detected in all cases using multichannel UV/Vis spectrophotometric measurements. The rate constants of the thermal back reaction of the betaines were determined at constant temperature by measuring the decrease in the maximum absorption intensity ( λ max ) with time. The half-lives ( t 1 / 2 ) and rate constants ( k ) of betaines under examination were calculated by plotting lnA against time ( t ). The kinetic measurements could be detected by both spectra scan and time-dependent decay measurements. Examination of the Arrhenius parameters reveals an underlying compensation between E a and log A , whereby an increase in E a is opposed by an increase in log A . The compensation appears in the corresponding Eyring parameters, Δ H ≠ and Δ S ≠ ; betaine structural changes that lead to lower, more favorable enthalpies of activation engender opposing entropic changes. At the isokinetic temperature T iso  =  β , structural changes do not affect the rate constant of a reaction series because the changes of Δ H ≠ are counterbalanced by changes of Δ S ≠ . The existence of an isokinetic relationship indicates a common structure of the transition state of all thermal back reaction of betaine under investigation. The computational results suggest that the decoloration reaction is a two-step mechanism. The first step corresponds to the transoid–cisoid isomerization with an activation barrier of 10.3 kJ mol −1 , and the second step is the ring closure from the cisoid intermediate with a barrier 71.3 kJ mol −1 , which represent the rate determining step for thermal decoloration. The photochemical ring opening of DHIs to betaines is a disrotatory 1,5-electrocyclic reaction, whereas the thermal ring-closing occurs in the conrotatory mode. Copyright © 2016 John Wiley & Sons, Ltd. The computational and experimental results suggest that the decoloration reaction is a two-step mechanism. The first step corresponds to the transoid-cisoid isomerization with an activation barrier of 10.3 kJ mol −1 , and the second step is the ring closure from the cisoid intermediate with a barrier of 71.3 kJ mol −1 , which represents the rate-determining step for thermal decoloration.