Isonitriles, group frequencies

A similar anchimeric rate-accelerating effect was observed for I and III (Table II). The infrared spectrum of I indicates that the isonitrile band is shifted by 34 cm.-1 to higher frequencies and that of III by 77 cm.-1. Hence in both complexes the isonitrile group is more ionic than in benzyl isonitrile and the same arguments should apply as to complex II. 

On the basis of enhancing of v(C=N) frequencies in the IR spectra of the complexes and NMR spectroscopy data it has been concluded [159, 165, 169], that the lanthanoid atom is bonded to carbon atoms of isonitrile group by a a-bond. The X-ray diffraction investigations have confirmed this supposition [72]. 

The carbonyl groups in nickel carbonyl may be replaced by isonitriles as well as by phosphines etc. 162) in general all the carbonyl groups are replaced in the direct reaction, but a compound (MeNC)3Ni(CO) has been obtained. Cotton and Zingales have measured the infrared spectra of a few of these compounds in the triple-bond region (46), and some interesting facts emerge. The frequencies are shown in Table III and it is clear that... 

The customary formulae of the nitriles R—C=N and the isonitriles R—N—C would point to a profound difference in bond character. It appears, however, from the same distances and from the same vibrational frequencies that the carbon-nitrogen bond is the same in both groups and actually bears mainly the character of a triple bond. The configuration (+) (-)... 

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