Absolute Configurations, Predominant Conformations and Tautomeric Structures of Enantiomeric tert-Butylphenylphosphine Oxides

Enantiomeric tert-butylphenylphosphine oxides have been isolated via resolution of the racemate with mandelic acid and investigated by using vibrational circular dichroism (VCD). Vibrational absorption and circular dichroism spectra of dextrorotatory, levorotatory, and racemic mixture of tert-butylphenylphosphine oxide have been measured in CDCl3 and CHCl3 solutions in the 2000−900 cm-1 region. Experimental spectra are compared with the ab initio predictions of absorption and VCD spectra obtained with density functional theory using B3LYP/6-31G* basis set for different tautomeric structures and conformers of (S)-tert-butylphenylphosphine oxide. This comparison indicates that (−)-tert-butylphenylphosphine oxide is of the (S)-configuration and indicates only one tautomeric structure and one conformation predominant for tert-butylphenylphosphine oxide in CDCl3 and CHCl3 solutions.