Ethylene complexes infrared spectra

The complexes obtained with simple monoolefins (305, 438, 486) are crystalline, yellowish-brown compounds, melting with decomposition below 100°C. Complex formation results in a shift to lower frequencies of the infrared C=C stretching vibration by about 100-150 cm (261, 438, 478). The molecular structure most commonly encountered in these complexes is the bridged dimer (198). The far-infrared spectrum of the ethylene complex dimer has a band at 427 cm assigned to the Pt-C2H4 stretching vibration (261). 

From these findings it was concluded that the polymerization must take place via a complex of all three components. It was established by diverse experiments that ethylene oxide enters into the complex with phenol in the form of an etherate. If the three components are added together in the appropriate proportions in a solvent, then a minimum is observed in the solubility, in vapor pressure, and in the relative permittivity (dielectric constant), together with a maximum in the density. A disappearance of the OH bands is observed in the infrared spectrum. Therefore, the complex must possess OH-inactive oscillations, i.e., in which the H atom lies in a plane between three oxygen atoms. The following formulation was proposed for the reaction ... 

The band at 1600 cm-1 due to a double-bond stretch shows that chemisorbed ethylene is olefinic C—H stretching bands above 3000 cm-1 support this view. Interaction of an olefin with a surface with appreciable heat suggests 7r-bonding is involved. Powell and Sheppard (4-1) have noted that the spectrum of olefins in 7r-bonded transition metal complexes appears to involve fundamentals similar to those of the free olefin. Two striking differences occur. First, infrared forbidden bands for the free olefin become allowed for the lower symmetry complex second, the fundamentals of ethylene corresponding to v and v% shift much more than the other fundamentals. In Table III we compare the fundamentals observed for liquid ethylene (42) and a 7r-complex (43) to those observed for chemisorbed ethylene. Two points are clear from Table III. First, bands forbidden in the IR for gaseous ethylene are observed for chemisorbed ethyl-... 

Various types of low-temperature cells are available commercially. Rochkind (1968) has presented a new low-temperature (20°K) technique, which provides a practical and sensitive method of infrared quantitative analysis of all infrared-absorbing gases and volatile liquids. The method, called pseudomatrix isolation spectroscopy (PMl), also provides a tool for the analysis of complex gas mixtures. The PMI method distinguishes between molecular isotopes, for example. Figure 3.21 shows a PMl spectrum of a mixture of isotopic d2-ethylenes (condensed on a 20 K Csl window). Rochkind claims that equivalent distinguishability has not been demonstrated with gas chromatography. 

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