Introduction to Nitrogen-Containing Organic Compounds

Chemistry organizes the compounds of carbon by their functional group -- the atom or

group of atoms that gives a molecule its characteristic reactivity -- and nitrogen forms

four functionally distinct groups when it bonds directly to a carbon skeleton. A nitro compound, $\text{R}-\text{NO}_2$, carries nitrogen bonded to carbon and doubly (in

resonance) to two oxygens; it is one of the two most common ways of introducing nitrogen

into an organic molecule via electrophilic or nucleophilic routes and is chiefly important

as a synthetic doorway to amines. An amine, $\text{R}-\text{NH}_2$ (or its

$N$-substituted forms $\text{R}_2\text{NH}$ and $\text{R}_3\text{N}$), is the organic

analogue of ammonia and is the most chemically important nitrogen family in this unit --

basic, nucleophilic, and the functional group present in countless natural products,

dyes, and pharmaceuticals. Cyanides ($\text{R}-\text{C}{\equiv}\text{N}$) and

isocyanides ($\text{R}-\text{N}{\equiv}\text{C}$) are a matched isomeric pair built

on the same $-\text{C}{\equiv}\text{N}$ pseudohalide unit, differing only in which atom

attaches to the carbon skeleton -- a difference so small on paper that it is easy to

mix up, yet so large in consequence that their hydrolysis and reduction chemistry point

to entirely different products. Finally, a diazonium salt,

$\text{Ar}-\text{N}_2^+\ \text{X}^-$, is formed only from an AROMATIC primary amine and

is arguably the single most versatile synthetic intermediate in this unit: nitrogen gas

is such a good leaving group that the diazonium carbon can be handed off to a huge range

of new substituents.

These four families are not studied in isolation -- they are linked by a chain of

interconversions that this chapter follows in order. A nitro compound reduces to a

primary amine; that same primary amine, if aromatic, diazotizes to a diazonium salt;

cyanides and isocyanides both reduce to amines (though to different classes of amine);

and the diazonium salt itself, once formed, opens up substitution chemistry that would

otherwise be impossible on a simple benzene ring. Throughout, WBCHSE's syllabus (Semester

IV, Unit 6) asks for real, mechanistic understanding of preparation routes, and for the

chemical reactions that let a chemist distinguish and interconvert these functional

groups -- not just their names.