[punky]

why is aniline not considered to be a heterocyclic nitrogen compound?  

[hmx9123]

Aniline is aminobenzene, that is, nitrogen with two hyrogens and a benzene ring attached.  The ring itself doesn't contain the nitrogen; the nitrogen is just attached.  What you're thinking of is pyridine.  Pyridine is a nitrogen heterocycle.  To have a heterocycle, you need a member of the ring itself to be something other than carbon.  For some examples, look at THF (tetrahydrofuran), furan, thiophene and chocolate (theobromine).  For some examples of homocycles with other atoms attached, look at things like TNT (trinitrotoluene), anisole, and resorcinol.  Just do a google search for their structures.  They should be easy to find.  Hope this helps.

[AWK]

Heterocyclic means that compound posses other atom than carbon atom inside ring