Vibrational Behavior of the −NO₂ Group in Energetic Compounds

Authors: Beal, Royce W.¹; Brill, Thomas B.¹

Source: Applied Spectroscopy, Volume 59, Issue 10, Pages 230A-246A and 1189-1303 (October 2005) , pp. 1194-1202(9)

Publisher: Society for Applied Spectroscopy

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Abstract:

The vibrational modes of the −NO₂ group in more than fifty energetic compounds containing the C-nitro and N-nitro functionalities were observed and then calculated in optimized structures using density functional theory (B3LYP/6-31+G^*). The trends in the symmetric and asymmetric stretches and scissor and out-of-plane deformations were explained by these calculations. A previously unreported correlation was found between the nitro group internal bonding angle and its asymmetric stretching frequency. The concept of meta and ortho/para directing groups was applicable to the trends in coupled motions in the nitroaromatic compounds. Both the scissor motion of C-NO₂ groups and the out-of-plane deformation of N-NO₂ groups were found to be virtually insensitive to the remainder of the molecule. These findings may be useful in analytical methods of explosive detection based on their infrared (IR) spectra.

Keywords: VIBRATIONAL ASSIGNMENTS; -NO2 GROUP MODES; ENERGETIC COMPOUNDS; EXPLOSIVE DETECTION

Document Type: Research article

DOI: 10.1366/000370205774430873

Affiliations: 1: Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716

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