The prediction of the absolute stereochemistry of primary and secondary 1,2-diols by 1H NMR spectroscopy: principles and applications.
The absolute configuration of 1,2-diols formed by a primary and a secondary (chiral) hydroxyl group can be deduced by comparison of the 1H NMR spectra of the corresponding (R)- and bis-(S)-MPA esters (MPA = methoxyphenylacetic acid). This method involves the use of the chemical shifts of substituents L1/L2 attached to the secondary (chiral) carbon, and of the hydrogen atom linked to the chiral center (C alpha-H) as diagnostic signals. Theoretical (AM1, HF, and B3 LYP calculations) and experimental data (dynamic and low-temperature NMR spectroscopy, studies on deuterated derivatives, constant coupling analysis, circular dichroism (CD) spectra, and NMR studies with a number of diols of known absolute configuration) prove that the signs of the delta delta(RS) obtained for those signals correlate with the absolute configuration of the diol. A graphical model for the reliable assignment of the absolute configuration of a 1,2-diol by comparison of the NMR spectra of its bis-(R)- and bis-(S)-MPA esters is presented.
Freire
Félix
F
Departamento de Química Orgánica and Unidad de NMR de Biomoléculas Asociada al CSIC, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
Seco
José M
JM
Quiñoá
Emilio
E
Riguera
Ricardo
R
D000438:Alcohols / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008968:Molecular Conformation; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism; D013696:Temperature
D000438:Alcohols