Steric requirements of 4JH-C-C-O-H- and 4JH-C-C-S-H-couplings

✍ Scribed by J.C. Jochims; G. Taigel

• Book ID: 104222998
• Publisher: Elsevier Science
• Year: 1968
• Tongue: French
• Weight: 309 KB
• Volume: 9
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)89809-3

✦ Synopsis

Hydroxyl protons in saturated systems H-C-C-O-E show *Jll II-couplings if the 9 protons and the connecting atoms are in a coplanar arrangement (Fig.l:y= 180' or O",s = 180' or 0') i,2) . Thus, not only the conformation of the hydroxyl group but also that of the hydroxyl proton is important, and a trans arrangement of a proton and a vicinal FIG.1.: Definition of the hydroxyl group alone is not a sufficient dihedral anglesy and a. condition for OH-long-range coupling. However, for pyranoses it has been shown 2) that the position of the hydroxyl proton of an axial anomeric hydroxyl group gauche to the ring oxygen and outside the ring has considerable statistical weight. Thus, if the C-atom adjacent to the anomeric center bears an axial proton a 4JH_C_C_O_H-co~pling should always be observable. This has been used in determining the configuration and conformation of many pyranoses 122) .

These considerations should also apply to other six membered cyclic hemiacetals. Thus, the proton resonance spectra a) of the dimers of acetoin, a) The spectra were recorded with a Varian HA-100 spectrometer.