For questions about the synthesis, properties, and reactions of organic compounds containing the -NO2 group i.e. nitro-compounds.
The nitro compounds are represented by $\ce{R-NO2}$. They can be described by using resonance structures such as these:
Nitro groups tend to be highly explosive due to their decomposition to form $\ce{N2}$, which is highly stable due to its very strong triple bond which results in the enthalpy of decomposition for nitro compounds tending to be high.
Nitro compounds are divided into two main categories; the more common aromatic nitro compounds, and the less common aliphatic nitro compounds.
Aromatic nitro compounds are generally synthesized using a 'nitrating mixture', a mixture of concentrated nitric and sulphuric acids, which generates the nitronium cation, $\ce{NO2+}$, that acts as an electrophile in an electrophilic aromatic substitution. However, strongly activated aromatic rings such as phenols can be nitrated using dilute nitric acid, or even in some cases nitrate salts. Aromatic nitro compounds are useful as precursors to aromatic amines or for deactivating the ring in nucleophilic aromatic substitution reactions.
Aliphatic nitro compounds are generally produced by nucleophilic substitution of halocarbons with nitrite salts, or by oxidation of primary amines. The $\alpha$ carbon is electrophilic, but the $\alpha$ hydrogen is acidic due to the electron withdrawing nature of the nitro group and so can often be deprotonated to form a nucleophilic carbanion which can undergo reactions such as the nitroaldol reaction.
