Configurational Assignment of 5-Substituted Pyrazolidin-3-ones Using Circular Dichroism Spectroscopy

Abstract

The chiroptical properties of the title compounds bearing various substituents at the N(1) and N(2) nitrogen atoms are discussed. It was found that the sign of the n−π* Cotton effect centered at about the 230−250 nm region can be correlated with the absolute configuration of the stereogenic center at C(5). It was also found that the sign of this Cotton effect is predictable by Weigang's lactam sector rule. MMX calculations, supported by X-ray measurements, showed that substituents at the nitrogen atoms significantly affect the conformation of the five-membered ring. It was additionally concluded that the conformation of the five-membered ring in 5-substituted pyrazolidin-3-ones is the sign-determining factor for an n−π* transition.

Complexation of rhodium(II) tetracarboxylates with aliphatic diamines in solution: 1H and 13C NMR and DFT investigations

“…Metal salt acts as a convenient chromophore; by this, one is able to establish absolute configuration of chiral compounds. [2][3][4][5][6][7] The second method is related to NMR spectroscopy and is based on the complexation of ligands with optically pure dirhodium salts, usually the salt of Mosher's acid (4R or 4S) or derivatives of amino acids. [8,9] These salts act as chiral recognition agents.…”

“…These parameters were positive for 1 H (>0 ppm) and either positive or negative for 13 C. In the fast ligand exchange regime, the decrease of Δδ magnitude in the course of titration implied the increase of molar ratio of free ligand to complex. (v) The use of multifunctional amines, such as 1,2-diazabicyclo[2,2,2]octane or 1,3,5,7-tetraazatricyclo [3,3,1,13,7]decane, resulted in polymeric adducts, insoluble in organic solvents. [30] This work is a continuation of our previous investigations and reports some NMR results on the complexation of rhodium(II) tetracarboxylates (Rh-Rh) with some aliphatic diamines (L-L) in CDCl 3 solution ( Fig.…”

Selective complexation of α-amino acids and simple peptides via their carboxylate groups

“…16 It occurs in some mono-and polynuclear lanthanide complexes, 17, 18 and in some dinuclear 4d and 5d metal complexes. 19,20 Carboxylate-O coordination has also been observed in ternary metal complexes designed to differentiate between L and D amino acids. 21 Here, the carboxylate coordination is enforced by an appended crown-ether moiety which binds the NH 3 + group via three strong NH⋯O hydrogen-bonding interactions.…”