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A systematic study of the absorbance of the nitro functional group in the vacuum UV region

NCJ Number
Analytica Chimica Acta Volume: 1185 Dated: November 2021
Courtney A. Crusea; John V. Goodpaster
Date Published
November 2021

In this research project, gas chromatography/vacuum UV spectroscopy (GC/VUV) was used to study the gas phase VUV spectra of various nitrated compounds (e.g., nitrate esters (-R-O-NO2), nitramines (R-N-NO2), nitroaromatics (Ar-NO2), and nitroalkanes (R-NO2)).


The nitro functional group (NO2) features strongly in compounds such as explosives, pharmaceuticals, and fragrances; however, its gas phase absorbance characteristics in the vacuum UV region (120–200 nm) have not been systematically studied. In the current study, the nitro absorption maximum appeared over a wide range (170–270 nm) and its wavelength and intensity were highly dependent upon the structure of the rest of the molecule; for example, the nitroalkanes exhibited a trend, in that the ratio of the relative absorption intensity between these two absorption features between the alkyl group (<150 nm) and the nitro group (200 nm) increased as the molecular weight increased. It was observed that the addition of multiple nitro functional groups on benzene or toluene resulted in an increase in intensity and blue shift from approximately 240 nm–210 nm. Nitrate esters exhibited an absorption between 170 nm and 210 nm and absorbance increased with increasing nitrogen content. The relative diversity of the spectra obtained was analyzed by Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). These calculations revealed that the spectra of all the compounds analyzed could be reliably differentiated without any misclassifications. (publisher abstract modified)