Nomenclature and Structure of Nitro Compounds

A nitro compound has the general structure $\text{R}-\text{NO}_2$, in which the

nitrogen atom is bonded directly to a carbon of the organic skeleton and carries a

formal positive charge balanced by a delocalised negative charge shared equally, by

resonance, over its two oxygen atoms -- the $\text{N}-\text{O}$ bonds in a nitro group

are experimentally identical in length, intermediate between a single and a double bond,

confirming this resonance delocalisation rather than one fixed $\text{N}=\text{O}$ and

one fixed $\text{N}-\text{O}^-$.

IUPAC nomenclature treats 'nitro-' exactly like a substituent prefix, cited in

alphabetical order among other substituents and given the lowest possible locant

consistent with the rest of the name: $\text{CH}_3\text{NO}_2$ is nitromethane,

$\text{CH}_3\text{CH}_2\text{CH}_2\text{NO}_2$ is 1-nitropropane,

$\text{CH}_3\text{CH}(\text{NO}_2)\text{CH}_3$ is 2-nitropropane, and

$\text{C}_6\text{H}_5\text{NO}_2$ is nitrobenzene. Like haloalkanes, nitroalkanes are

classified as primary, secondary or tertiary according to how many carbon groups are

attached to the nitro-bearing carbon: a $1^\circ$ nitroalkane has the $-\text{NO}_2$ carbon

bonded to one other carbon, a $2^\circ$ nitroalkane to two, and a $3^\circ$ nitroalkane to

three (e.g. 2-methyl-2-nitropropane).

A nitro group must be carefully distinguished from its isomer, an alkyl nitrite

($\text{R}-\text{O}-\text{N}=\text{O}$), in which the organic group is bonded to nitrogen

through an intervening OXYGEN rather than directly -- the two are constitutional isomers

of identical molecular formula but entirely different connectivity, reactivity and …