1 H nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and electron delocalization in triphenylphosphine

• Published in: Canadian journal of chemistry 1993-05, Vol.71 (5), p.639-643
• Main Authors: Schaefer, Ted, Sebastian, Rudy, Hruska, Frank E.
• Format: Article
• Language: English
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v93-085

The 1 H nuclear magnetic resonance spectral parameters are reported for triphenylphosphine as solutions in CS 2 /C 6 D 12 and acetone-d 6 at 300 K. The internal rotational potential opposing torsion about the P—C bond is computed by AMI and STO-3G MO methods. The computed potentials are used to calculate the average shielding of the para protons caused by the diamagnetic anisotropies of the neighbouring phenyl groups. The results are used to estimate the degree of electron delocalization from the lone pair on phosphorus. The extent of delocalization depends on the internal motions and comparisons are made with phenylphosphine. The maximum possible screening of the para protons in phenylphosphine is calculated as 0.19 ppm for a conformation in which the lone pair on phosphorus is oriented perpendicular to the aromatic plane. The intramolecular rotational potentials then yield 0.02 9  ppm as the shielding of the para protons in triphenylphosphine due to electron delocalization, just as found for the CS 2 /C 6 D 12 solution after correction for diamagnetic anisotropy fields.