Nitrile substitutents, group frequencies

Chapter 4 examines the group frequencies of triple bonds and cumulated double bonds. The alkyne hydrocarbons (acetylenes, —C=C—) are treated in I and the important nitrile group, —C=N, in detail in II. In the case of the alkynes the amount and type of substitution can often be identified from vibrational data (I, D, E). Systems containing cumulative double bonds (so-called back-to-back double bonds, >C=C=C<) such as the allenes in the hydrocarbon series are considered in III. A number of them contain hetero-atoms as for example, the ketenes (>C=C=0, III, B). Section F presents a problem that allows the reader to determine which of two possible structures is the correct one based on infrared and Raman data. 

Nitrile groups in the substrate may also cause problems. Minnaard, Feringa and de Vries reported the enantioselective hydrogenation of a range of substituted 2-acetamido-cinnamates at 5 bar pressure using Rh/MonoPhos. Whereas most substrates could be hydrogenated with turnover frequencies (TOFs) of between 200 IT1 and 600 h-1, the 4-cyano-substituted substrate was hydrogenated very slowly at this pressure with a TOF of only 4 h 1 [40]. 

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