What is this organic ring called?

[ShawnD]

What is the name of what looks like a benzene ring but one of the carbons is replaced with a nitrogen?

 

[Monique]

A pyridine

for some other heteroannules:

Just as a carbon atom in a hydrocarbon chain can be replaced by heteroatoms to give, for example, ethers or amines, so can the carbons of aromatic rings such as those described above be replaced by heteroatoms to give HETEROAROMATIC systems.

Nitrogen as replacement heteroatom in benzene:

To formally replace a C atom of benzene, nitrogen must fulfill the same orbital and electronic criteria as the carbon it is to replace, i.e. it must be sp2-hybridised and have the same number of electrons (the principle of isoelectronic replacement).

Replacing one carbon with a nitrogen yields pyridine.

Replacing two carbons in different positions can yield a variety of componds like pyridazine (1,2-diazine), pyrimidine (1,3-diazine), or pyrazine (1,4-diazine).

Replacing three carbons with three nitrogens generates 1,3,5-triazine and replacing four carbons by four nitrogens produces 1,2,4,5-tetrazine.

Oxygen as replacement heteroatom in benzene:

For oxygen to achieve the same orbital and electronic requirements as a carbon in benzene it has to lose an electron becoming O+. By replacing one carbon in benzene with an O+, a pyrilium cation is formed.

Sulphur as replacement heteroatom in benzene:

For sulphur to achieve the same orbital and electronic requirements as carbon it also has to lose an electron becoming S+. By replacing one carbon in benzene with an S+, a thiopyrilium cation is formed.

http://www.dcu.ie/~chemist/pratt/annulene/annulene.htm