Alkanes infrared absorption frequencies

Table 12.5 Infrared Absorptions of Alkanes, Alkenes, Alkynes, and Arenas Frequency Hydrocarbon Vibration (cm ) Intensity ... 

The infrared spectra of the alkanes show clearly absorptions corresponding to the C—H stretching frequencies at 2850 cm 1 to 3000 cm-1. The C—C stretching absorptions have variable frequencies and are usually weak. Methyl (CH3—) and methylene (—CH2—) groups normally have characteristic C—H bending vibrations at 1400 cm-1 to 1470 cm-1. Methyl groups also show a... 

Injection of ethene at 150°C or above produces a new infrared band at about 1500 cm (Figure 6), which is in the frequency range characteristic of partially unsaturated C-C bonds. Alkanes are detected in the gas phase above zeolites heated in the presence of ethene, and an intense absorption band appears in the ultraviolet-visible spectrum of ZSM-5 on heating in ethene to 100°C at 280 nm which has been attributed to an allyl carbenium cation (refs. 

Examples of these infrared bands are seen in Fig. 8.7. The first two rows of spectra illustrate benzene rings with alkane substituents. For these, the adjacent hydrogen wag bands tend to increase in frequency somewhat as the a carbon of the substituent is more highly substituted. We can note absorptions for toluene at 728 cm ethylbenzene at 745 cm isopropylbenzene at 759 cm and /ert-butylbenzene at 763 cm ... 

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