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

Abstract

. Can. J. Chem. 71, 639 (1993). The 'H nuclear magnetic resonance spectral parameters are reported for triphenylphosphine as solutions in CS,/C6D12 and acetone-d6 at 300 K. 'The internal rotational potential opposing torsion about the P-C bond is computed by AM1 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 0.029 ppm as the shielding of the para protons in triphenylphosphine due to electron delocalization, just as found for the CS2/C6D12 solution after correction for diamagnetic anisotropy fields.TED SCHAEFER, RUDY SEBASTIAN et FRANK E. HRUSKA. Can. J. Chem. 71, 639 (1993). On a dCtermint les parametres des spectres de rksonance magnCtique nuclCaire du I H dCterminCs 2 300 K pour des sohtions de triphCnylphosphine dans du CS,/C6D12 ou de llacCtone-d6. Faisant appel i des mCthodes AM1 et STO-3G, on a calculi5 le potentiel de la rotation interne qui s'oppose i la torsion autour de la liaison P-C. On a utilisC les potentiels ainsi CvaluCs pour calculer le blindage moyen des protons en para provoque par les anisotropies diamagnktiques des groupes phCnyles avoisinants. On utilise les rCsultats pour Cvaluer le degrC de dClocalisation Clectronique de la paire libre du phosphore. Le degrC de dClocalisation dCpend des mouvements internes et on fait des comparaisons avec la phCnylphosphine. On a CvaluC que le maximum de blindage des protons para de la phCnylphosphine est Cgal 5 0,19 ppm pour une conformation dans laquelle l a paire dlClectrons libres sur le phosphore est orientee perpendiculairement par rapport au plan du noyau aromatique. A cause de la delocalisation Clectronique, les potentiels de la rotation intramolCculaire ajoutent alors O,O2, ppm au blindage des protons para de la triphCnylphosphine, comme on l'a observe pour la solution dans le CS2/C6D,,, apres correction pour les champs d'anisotropie diamagnCtique.[Traduit par la ridaction]

A precise analysis of the 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane. Ring pucker, signs of long-range J(H,H), internal rotational barrier, and van der Waals shifts

“…To isolate these differential shifts from those caused by the diamagnetic anisotropy, AX, of the phenyl group in 1, the model in ref. 36 was applied. This model relates the shift cause by AX to (sin20), the expectation value of sin20, where 0 is the torsion angle about the csp3-csp2 bond in 1.…”

Phosphorus-31 Chemical Shift Anisotropies in Solid, Octahedral Chromium(0) Triphenylphosphine Derivatives

“…13 Since the precise C 3 symmetry at the phosphorus site does not exist in the crystal lattice, 14 the question arises whether averaging of the perpendicular components results from large-amplitude motions of the phenyl rings. 15 A lowtemperature measurement, at 133 K, was performed, which showed that the shift anisotropy and span were essentially unchanged. The measured values for the individual shift tensor elements are given in Table 1 and are in good agreement with those reported previously.…”

“…The shielding tensor of PPh 3 has been investigated previously, but only at room temperature, and an axially symmetric powder pattern was observed . Since the precise C 3 symmetry at the phosphorus site does not exist in the crystal lattice, the question arises whether averaging of the perpendicular components results from large-amplitude motions of the phenyl rings . A low-temperature measurement, at 133 K, was performed, which showed that the shift anisotropy and span were essentially unchanged.…”

1H nuclear magnetic resonance and molecular orbital studies of 2-formylstyrene. Three significant nonplanar conformers at 300 K

“…The barrier to internal rotation in benzaldehyde is calculated as 37.5 kJ/mol with the 6-31G* basis (18), rather highe? than, for example, the free energy of activation of 32.2(6) kJ/mol in solution (19)(20)(21).…”