[mrlucky0]

During lecture my professor mentioned that indole was electron rich. I'm not sure why this is so especially when other similar nitrogen heterocycles: pyridine, quinoline, pyrazine considered electron deficient. What about these heterocycles that make them electrophilic? What about other heterocycles like pyrrole or thiazole?

I'm sure whether the ring is electron deficient or electron rich has to do with the electronegativity of the atom, but are there other factors?  I hoping someone can clarify this. Thanks.

[agrobert]

Heteroatom deficiency has to do with hybridization and whether or not the lone pair electrons on say nitrogen (indole) contribute to the aromaticity of the system.  Indole is aromatic, the lone pair electrons are involved in the system yet it is electron rich in that it can push its lone pair towards the double bond and become nucleophilic at the 3 position.

Indole

http://en.wikipedia.org/wiki/Indole

is a special case heterocycle.  Read about it and you will understand what is meant by electron rich or deficient.  Nitrogen in heterocycles can function as bases, catalysts, and nucleophiles.  It all depends on the elctronics of the structure.

Think about it.