Nitro compounds infrared frequencies

Nitro groups of nitroalkanes can be identified by strong infrared bands at about 1550 cm-1 and 1375 cm-1, whereas the corresponding bands in the spectra of aromatic nitro compounds occur at slightly lower frequencies. A weak n —> n transition occurs in the electronic spectra of nitroalkanes at around 270 nm aromatic nitro compounds, such as nitrobenzene, have extended conjugation and absorb at longer wavelengths ( 330 nm). 

In general, there are three regions of the infrared (IR) spectra that merit special attention. Bands in the range 2400-2100 cm can be assigned to the N-N stretching frequency of adsorbed N2 or N20, bands below 1700 cm" can be attributed to oxidized nitrogen species (nitrite, nitrate, and nitro compounds), and those around 3800-3600 cm" to hydroxyl groups.Table 4.1 summarizes the main IR bands identified for a Rh/ceria catalyst in contact with a NgO/He flow. 

Spectroscopic evidence confirms the fact that the two Meisen-heimer compounds (36), that formed from s-trinitroanisole and eth-oxide ion and that formed from s-trinitrophenetole and methoxide ion, are identical. The two products give identical infrared t45) and visible spectra (46). The infrared spectrum is characterized by a shift in the N-0 symmetrical stretching frequency from 1343 cm. in s-trinitroanisole to 1291 cm. in the product and a shift in the N-0 asymmetrical stretching frequency from 1552 to 1492 cm. b These differences can be attributed to increased negative chai on the nitro groups and are consistent with the proixtsed structure 111. 

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