Peculiarities of the interaction of phosphorus with the aromatic ring and their consideration in connection with the problem of conjugation

Gas Phase Detection of the NH–P Hydrogen Bond and Importance of Secondary Interactions

“…The spectra of the NH-stretch for these complexes and the DMA monomer are compared in Figure , in which this trend is clear. The weakness of phosphorus as a hydrogen bond acceptor relative to nitrogen in aliphatic compounds has also been mentioned in previous liquid phase experiments. ,, …”

“…The weakness of phosphorus as a hydrogen bond acceptor relative to nitrogen in aliphatic compounds has also been mentioned in previous liquid phase experiments. 12,14,28 In gas phase experiments with MeOH as the hydrogen bond donor and the same four acceptor molecules, the same order was observed for the relative hydrogen bond strength of the acceptors, albeit with much larger red shifts in the range 103− 333 cm −1 . 9 However, with MeOH as donor, DME was more comparable to DMS and TMP in terms of relative strength, whereas the superiority of TMA as a hydrogen bond acceptor was similar for the MeOH and DMA hydrogen bond donors.…”

“…The measured red shifts of the fundamental OH-stretching frequency in PhOH were OH···N (556 cm –1 ) > OH···P (333 cm –1 ) > OH···O (274 cm –1 ) > OH···S (251 cm –1 ) . In a very similar experiment, using Bu 3 Y and Bu 2 Y as hydrogen bond acceptors instead, the following order of hydrogen bond strength was observed: OH···N (800 cm –1 ) > OH···O (280 cm –1 ) > OH···S (254 cm –1 ) > OH···P (240 cm –1 ) . Despite the differences between the results for Et n Y and Bu n Y as hydrogen bond acceptors, they both predict that the OH···N hydrogen bond is significantly stronger than the OH···Y (Y = P, O, and S) hydrogen bonds, which are of comparable strengths.…”

“…Different investigations of the PhOH–Ph 3 P and PhOH–Ph 3 N hydrogen-bonded complexes, all based on the experimentally observed red shift of the fundamental OH-stretching frequency, have found different relative strengths of N and P as hydrogen bond acceptors. Although the exact reason for this discrepancy is not known, it may arise from the use of different solvents. ,, Also, in these compounds, XH···π hydrogen bonds form, which makes the experimental results with the Ph 3 Y hydrogen bond acceptor difficult to compare to the other results.…”

“…Recently, the OH···P hydrogen bond in bimolecular alcohol–trimethylphosphine (TMP) complexes was observed in the gas phase at room temperature . In addition, a number of studies on the OH···P hydrogen bond have been performed in the liquid phase and in cooled matrices. − In most of the liquid phase studies, different alcohols (e.g., methanol, MeOH, ethanol, EtOH, and phenol, PhOH) act as the hydrogen bond donor forming complexes with different P containing molecules (e.g., triethylphosphine, Et 3 P, tributylphosphine, Bu 3 P, and triphenylphosphine, Ph 3 P) in various inert solvents. − ,− Several of these studies conclude that P is a significantly weaker hydrogen bond acceptor than N in the OH···Y (Y = N, P) hydrogen bond, which highlights the difficulty in detecting complexes with P as a hydrogen bond acceptor. ,,, …”