Stereochemistry of cyclopentane derivatives from ^{2, 3}J_CH dependence on dihedral angle (θ HCCX)

Abstract

The (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained (2,3)J(CH) values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of (3)J(CH) and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88).

Novel Triazole-Quinoline Derivatives as Selective Dual Binding Site Acetylcholinesterase Inhibitors

“…To assign the correct olefin stereochemistry, we performed the G-BIRD R.X -CPMG-HSQMBC [23,24] experiments to measure heteronuclear spin-spin coupling constant C-H ( 3 J CH ) between olefinic hydrogen and carbonyl carbon. According to Karplus equation, vicinal coupling constants present a strong correlation with the dihedral angle (θ) enabling correlation of the 3 J CH value with E (θ = 0°) or Z (θ = 180°) stereochemistry of the double bond [25,26]. Thus, in this case, the 3 J CH = 6.9 Hz was observed in the NMR experiment, which corresponds to θ around 0°, confirming the exclusive presence of isomer E as expected, due to the most favorable anti elimination in the E1cB reaction, giving rise to a more stable E -isomer [27].…”

Physical methods and techniques : NMR spectroscopy

“…70 The relationship between experimentally obtained 2 J CH / 3 J CH couplings and computed C-C-C-H dihedral angles can infer the relative stereochemistry in cyclopentane derivatives. 71 Room-temperature ionic liquids have been studied using ionic conductivity, 1 H, 7 Li and 19 F diffusion and Arrhenius plots of T 1 relaxation. 72 The empirical expression for 1 J CLi = L[n(a + d)] À1 is proposed; a reciprocal dependence on two factors: (i) the number n of lithium nuclei in bonding contact, and (ii) the sum of anions (a) and donor ligands (d) coordinated at the Li nucleus (L is a sensitivity factor).…”

Unequivocal structural assignments of three cycloheptenoid intermediates for guaiane sesquiterpenes: an experimental and theoretical approach

“…Nuclear magnetic resonance is a very important and well‐established tool for the structural analysis of organic compounds . NMR spectra are a highly valuable source of information on molecular structure because of the sensitivity of the measured parameters to changes in the conformation of a molecule and its local environment .…”