Application of carbon-13 NMR spectroscopy to acyclic conformational analysis

Assignment of Relative Configuration to Acyclic Compounds Based on13C NMR Shifts. A Density Functional and Molecular Mechanics Study

“…There are only two low energy rotamers in the ethyl group possible, since the third would lead to a syn-pentane interaction. One should note the low field shift of C-19 in 13a and 13c , which can be qualitatively understood following the argument of Whitesell . When going to 14 the same local conformations that lead to the low field shift of C-19 in 13a and 13c are found at higher energy ( 14d , 14e ) and are therefore of less importance for the average shift of 14 .…”

“…For organic compounds comprising larger carbon skeletons with multiple stereocenters, the interpretation of chemical shifts has mainly been done by means of empirical increment systems and by Whitesell and co-workers have been applied to some 3,5-dimethylated hydrocarbons and alcohols (e.g. 1 , 3 ).…”

Crystalline order in probably hollow micellar fibers of N-octyl-D-gluconamide

“…Carbon atom C-3 is more shielded, and the resonance signal appears at higher field (70.51 ppm) because its methine proton is gauche to both the neighboring methine protons. 43 The remaining peaks at 74.58 and 63.88 ppm can be safely ascribed to C-2 and C-6 ( Table 2). Due to the rearrangement from the 4G+ sickle (solution) to the planar conformation (crystal) hydrogen atoms 4-H and 5-H reorientate from gauche to anti, resulting in smaller shift differences between the signals of C-4/C-5 and (2-2.…”

Epoxidation of 5-(tosylamido)-3-hexen-2-ol derivatives. Stereochemical assignment of product configuration by NMR and molecular mechanics studies

“…Direct investigations have been attempted for vicinal polyacetates24 and po-lyols25 via homonuclear coupling constants in conjunction with molecular modeling studies. The relative and absolute stereochemistry of vicinal aminopolyols has been determined by circular dichroism (CD) after introduction of a chromophore.26 An empirical method based on steric effects of -substituents on 13C NMR chemical shifts has been suggested by Whitesell et al, 27 and empirical relationships between stereochemistry and NMR parameters have been found for various groups of compounds.…”