Substituent, temperature and solvent effects on tautomeric equilibria in several β-ketoamides have been investigated by means of nuclear magnetic resonance spectroscopy (NMR). Keto-enol equilibrium predominates over the amide-imidol one. The relative stability of the individual tautomers and the corresponding equilibrium shifts are explained considering electronic and steric effects and tautome...

Density functional theory (DFT) calculations have been performed to calculate the optimized geometries of stepwise fluorinated methylenecyclopropanes and 1-methylcyclopropenes. Increasing the number of fluorine atoms caused a destabilization of methylenecycopropane. Perfluorinated 1-methylcyclopropene was found to be present in substantial concentration. This is supported by calculations of the...

Ultraviolet and infrared absorption spectroscopy, in aqueous and non-aqueous media, have been employed to study the tautomerism of 9-substituted isoguanines, including the nucleoside isoguanosine. With the aid of a series of model compounds, it was shown that 9-substituted isoguanines, and isoguanosine, in aqueous medium are predominantly in the form N (1) H, 2-keto-6-amino. In dioxane solution...

This thesis presents computational chemistry studies of keto-enol reactions and chromophores of photobiological significance. The first part of the thesis is concerned with two protein-bound chromophores that, depending on the chemical conditions, can exist in a number of different ketonic and enolic forms. The first chromophore is astaxanthin, which occurs in the protein complex responsible fo...

(a) Draw the bi-molecular complex (see Figure 2 in the paper) using Avogadro. (b) Optimize the structure at B3LYP/6-31G** level of theory. (c) Prepare an input file for a relaxed scan (same level of theory) of the proton transfer using the modredundant option (check the manual page for opt ). Please include the option maxcyc=8 regarding the optimization. (Hint: which geometrical parameter do yo...

androstane skeleton with a keto-enol tautomerism at the cyclopentane ring. Wecarried out further isolation for PFTase inhibitors from the cultured broth of strain FO-3929 and found andrastin D (4, Fig. 1). In this paper, fermentation, isolation, structure elucidation, and biological properties of 4 are described. A stock culture of strain FO-3929 was inoculated into six 500-ml Erlenmeyer flasks...

Biologically and pharmaceutically active core structures containing a new class of 4-hydroxy-α-carbolines, dihydropyrido[2,3-b]indoles, pyrimido[4,5-b] and [5,4-b]indoles have been synthesized in good yields via Pd-catalyzed amidation and cyclizations. The keto-enol tautomerism in 4-hydroxy-α-carbolines has been investigated by DFT calculations and spectroscopic techniques. The fluorescence stu...

In this laboratory exercise we will measure the Equilibrium Constant Kc for the keto-enol tautomerism of two -diketones and two -diketoesters. This will be accomplished by measuring the signal strength of key protons in the Nuclear Magnetic Resonance (NMR) spectrum of the equilibrium system. The influence of the solvent on the equilibrium position will be examined by considering the measured ...