Conformational Isomerism of 3-Chalcogenomethyl--Methyl-2-Pyrrolidinones: Insights from NMR Spectroscopy and Molecular Modeling.

A conformational analysis of -methyl-2-pyrrolidinone 3-substituted by methoxyl, thiomethoxyl, and selenomethoxyl is reported by means of H nuclear magnetic resonance spectroscopy and electronic structure calculations. The five-membered ring has an envelope conformation with the α-carbonyl substituent being able to assume two positions: pseudo-axial and pseudo-equatorial. In vacuum, the calculations pointed to the pseudo-axial conformer as the most stable one, and this preference increases with the size of the substituent and a decrease in its electronegativity.

Antioxidant activity of and -amyrin isolated from leaves.

Brazil has a great variety of native plants which could be explored and among them guabiju () stands out. Thus, this study consisted of isolating pentacyclic triterpenes, and -amyrin from guajibu leaves, and determine the antioxidant activity.The leaves were dried, pulverized and submitted to a dynamic maceration process with ethanol 96° GL, concentrated to obtain crude leaf extract (CLE).

NMR spectroscopy and theoretical calculations in the conformational analysis of 1-methylpyrrolidin-2-one 3-halo-derivatives.

This study reports the results of ab initio and density functional theory (DFT) electronic structure calculations as well as (3)J(HH) experimental and calculated coupling constant data obtained in the investigation of the conformational equilibrium of 3-halo-derivatives of 1-methylpyrrolidin-2-one. The five-membered ring assumes an envelope conformation owing to the plane of formation of the O═C-N-R bond, with C4 forming the "envelope lid". When the conformation changes, the "lid" alternates between positions above and below the amide plane.