Nitriles infrared absorptions

Poly(a-phenylethyl isocyanide), however, yields complex products distinguishable from monomer upon thermal degradation at 20 mm Hg (13). At 300° C a viscous condensate is produced which is free of isocyanide absorption in its infrared spectrum and appears very similar to the recently synthesized oligo-isocyanides, a,co-dihydrotri(a-phenylethyl isocyanide) and a,co-dihydrohexa(a-phenylethyl isocyanide) (15). Pyrolysis at 500° C produces an intense broad infrared absorption band in the range about 3300 cm-1, which is the range of associated N il bonds. Pyrolysates obtained at 700° C reveal nitrile absorption at 2270 cm"1, that becomes more intense in pyrolysates produced at temperatures up to 1300° C. A slow pyrolysis at 200-300° C is indicated for the study of primary structural changes in poly(a-phenylethyl isocyanide). Pyrolysates of poly(<7-... 

The butadiene (80%)-acrylonitrile(17%)-aerylamidoxime(3%) terpolymer was prepared by reacting 2.5g butadiene 80%)-acrylo-nitrile(20%) copolymer (Aldrich) in 150 ml xylene with 1.61g hydro-xylamine hydrochloride in 12 ml n-butanol (freed of HC1 immediately before addition by method of Hurd (4) by dropwise addition under nitrogen. Reaction time and temperature were 23 hr. and 90-95°C. The polymer product was worked up by slowly adding the reaction mixture to 500 ml ether with rapid stirring. The precipitated polymer was allowed to settle, the supernate decanted and the polymer resuspended and washed with two 100 ml portions of ether followed by vacuum drying. Yield 2.04g (81%). Conversion of nitrile functional groups to amidoxime groups was 15% by infrared absorption. 

Infrared spectroscopy is a valuable tool for the structural analysis of acid derivatives. Ajrid chlorides, anhydrides, esters, amides, and nitriles all show characteristic infrared absorptions that can be used to identify these functional groups in unknowns. 

TABLE 21.3 Infrared Absorptions of Some Carbonyl Compounds and Nitriles... 

P5rrolysis at 500°C produces an intense broad infrared absorption band 3,300 cm , cissociated with N-H bonds Pyrolysates at 700°C reveal nitrile absorption at 2,270 cm Nitrile absorption at 2,270 cm becomes more intense in pyrolysates produced up to 1,300°C... 

Figure 17.3 shows an annotated spectrum of propanoic acid. Nitriles show an intense and characteristic infrared absorption band near 2250 cm that arises from stretching of the carbon—nitrogen triple bond. 

R. E. Kitson and N. E. Griffith, Infrared Absorption Band Due to Nitrile Stretching Vibration, Anal. Chem. 24, 334, 1952. 

As particular types of vibration always occur at a similar wavenumber, it is possible to build up a table of characteristic absorptions. Such a table is given on p. 14 of the SQA Data Booklet. If you examine this table, you will see, for example, that an absorption in the wavenumber range 2260-2215 cm is indicative of a nitrile group and is due to stretching of the C=N bond. So, given the infrared spectrum of an unknown organic compound and a table of characteristic absorptions, it should be possible to identify the functional groups present in the compound. In most cases, however, more information is required to determine the full structure. 

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