P—H Stretching Vibration

A number of inorganic and organic phosphorus compounds containing the P—H linkage have been examined by various workers [1, 5—7, 27, 28, 32, 36, 47—51], and in these a sharp absorption band of medium intensity occurs in the range 

The P—H deformation modes appear to be less useful. Nyquist [39] has identified a characteristic band in dialkyl phos-phonates in the 968—979 cm region which is strong and is deuterium sensitive, and he assigns this to the 8 PH vibration. However in a wider range of compounds this band appears to extend over the range 1015—897 cm and it is not of much value for identification purposes. 

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Band Assignments and Structure Elucidation.— The conjugated A -phospholens can be distinguished from A -phospholens by the low frequency ca. 2225 cm ) of their P—H stretching vibrations. The i.r. and Raman spectra of the chloride (122)... 

PH2D, PHD2. The frequency of the P-H stretching vibration in PHD2, v = 2323.81 cm" was determined by Fourier transform spectroscopy and used together with the overtone 2v = 4563.26 cm" to derive co(P-H) = 2408.17 cm" treating the P-H unit as a diatomic molecule [12]. - For the fundamental frequencies of the species in solid phases, see p. 192. 

Hunt JH, Guyot-Sionnest P, Shen YR. 1987. Observation of C H stretch vibrations of mono-layers of molecules. Optical-sum frequency generation. Chem Phys Lett 133 189-192. 

Figure 6.25 shows the 3q band of HCN in which v3 is the C—H stretching vibration. The transition is of the Z+-Z+ type showing clear P- and i -branch structure like a diatomic molecule. However, unlike a diatomic molecule, there are two hot bands, involving lower states in which the low-wavenumber bending vibration v2 is excited, overlapping 3q. One band shows a P,Q and R branch with the band centre at about 3292 cm 1 and the other a P and an R branch with the band centre at about 3290 cm-1. 

Portions of the infrared absorption spectrum of HCN. The bending vibration is a perpendicular band and therefore has allowed P, Q, and R branches. The [C-H stretching] vibration is a parallel band with Pand. / branches only. 

Huisken, F., Kulcke, A., Laush, C., and Lisy,. 1. M., Dissociation of small methanol clusters after excitation of the O—H stretch vibration at 2.7 p, J. Chem. Phys. 95, 3924-3929 (1991). Bleiber, A., and Sauer, J., The vibrational frequency of the donor OH group in the H-bonded dimers of water, methanol and silanol. Ab initio calculations including anharmonicities, Chem. Phys. Lett. 238, 243-252 (1995). 

The bicyclic phosphazene III forms colorless crystals that are stable in air and melt sharply at 124°. The compound is readily soluble in petroleum, benzene, chloroform, and dichloromethane but insoluble in water. The IR spectrum of the compound shows a broad absorption band at 1195 cm" attributable to ring P=N stretching vibration. The H NMR spectrum is discussed in the literature,The P H NMR spectrum is that of an A2BC spin system (8 18-24). The structure of the compound has been established by X-ray crystallography. The crystals are monoclinic with space group C2/c, a = 10.81, b = 17.52, c = 28.48 A, p = 94.8° with eight molecules in the unit cell. 

There are also several characteristic phosphate group vibrations, e.g, strong bands due to the P==0 stretching vibration, namely. an asymmetric POj stretch at around 1228 cm i and a symmetric I stretch at 1084 cm h There are P—O stretching modes in the reg between 900 and 800 cm but these are obscured by strong w< absorption in this range. 

The doublet that is observed in the range 2860-2700 cm for an aldehyde is a result of Fermi resonance (p. 17). The second band appears when the aldehyde C—H stretching vibration is coupled with the first overtone of the medium intensity aldehyde C—H bending vibration appearing in the range 1400-1350 cm . ... 

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