Conformation of a saturated 13-membered ring

Abstract

less than 0.7%, which was worse than that for 14C (<0.3%).Kinetic isotope effects were then calculated by nonlinear regression analysis with use of eq 2 in the text. Error limits shown in Table I are the standard deviations of the isotope effect values calculated for each x with use of eq 4, in which was the value determined by regression analysis with use of eq 2.

Conformational Studies of Dodecanolactone by Dynamic NMR Spectroscopy and Computational Methods

“…The calculated free-energy difference for these two conformations was too small for assignment on this basis alone, and carbon chemical shifts calculated by using the GIAO [19] method provided additional support. [15][16][17] The finding of the same [337] ring conformation in each of these five compounds provides support for the suggestion [17] that geminal disubstitution in α,ω-bis(methyldodeca-1,12-diylammonio)hexane dibromide [13] and dimethyl 1-hydroxycyclotridecylphosphonate [14] may contribute to the change in conformation for these two compounds. [15][16][17] The finding of the same [337] ring conformation in each of these five compounds provides support for the suggestion [17] that geminal disubstitution in α,ω-bis(methyldodeca-1,12-diylammonio)hexane dibromide [13] and dimethyl 1-hydroxycyclotridecylphosphonate [14] may contribute to the change in conformation for these two compounds.…”

“…Another communication, by Goto and Osawa, [12] reported a conformational search for cyclotridecane and other cycloalkanes by a corner-flapping method and also used Allinger's MM2 force field. [10] The X-ray structure [13] of α,ω-bis-(methyldodeca-1,12-diylammonio)hexane dibromide showed a quinquangular [13333] conformation for an ordered model and a similar [13333] and a [346] conformation for a disordered model. From the coordinates, we generated the lowest-energy conformation and found that the dihedral angles corresponded to the same [337] conformation found in the stochastic search.…”

Conformational analysis of cycloalkanes

“…Low-temperature NMR studies have been one of the best methods to study conformational equilibria of cycloalkanes. Cyclotridecane undergoes a fast pseudorotation and low-temperature NMR studies did not yield any useful results [46]. According to the strain energy calculations, there are five low-energy conformations, which are separated by low energy barriers (Fig.…”

“…Two quinquangular conformations are of the lower energy, while three triangular are of somewhat higher. Based on the calculations [48] and the studies of related systems [46,49] [46,47] to be the lowest energy conformation.…”

Medium-sized rings: conformational preferences in cyclooctanone driven by transannular repulsive interactions

“…Torsional strain and non-bonded transannular interactions are expected to be more important in determining ring conformation. 22 Several studies of medium-sized rings were conducted using X-ray crystallography, 23,24 NMR spectroscopy [25][26][27][28] and electron diffraction, 17,20 mostly during the 70s and 80s. These techniques provide very valuable structural information, but they have limitations to characterise multi-conformational systems.…”