STRUCTURES AND VIBRATIONAL SPECTRA OF NITRO-BENZO[A]PYRENE AND NITRO-BENZO[E]PYRENE ISOMERS: ......

The nitro polycyclics' toxicity and reactivity have been linked to their molecular structure and electrical characteristics, particularly the nitro substituent orientation. Because experimental data for mononitro derivatives of benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP) is limited, density functional B3LYP/6-311++G(d,p) calculations on all isomers of nitro-BaP and nitro-BeP in their singlet and triplet states were done. Although the majority of structures are non-planar, planar forms in which NO2 interacts with the aromatic -electron system are the most stable. In both BaP and BeP, nitro substitution in the bay region yields in two stable singlet structures with significantly distinct geometries; the higher energy states show a strong O–C interaction that triggers sp3 hybridization in the aromatic carbon atom. The estimated IR spectra show variations between planar and non-planar structures, which can be utilised to forecast the nitro group orientation and hence the isomer's potential toxicity.

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