what are the four main classes of organic compounds?

Answer 1

It used to be thought that they were (I) aliphatic, meaning straight and branched chain hydrocarbons of all kinds, together with all their functional groups.

Next came (II) alicyclic, meaning rings of carbon compounds, together with all the functional groups.

Next came (III) aromatic compounds, including benzene, naphthalene, anthracene, and phenanthrene, together with functional groups.

Finally (IV) came heterocyclic compounds in which rings of carbon atoms are interspersed with N, O, or S atoms.

Modern organic chemistry does not classify compounds un Aristotelian categories like this.

Answer 2

1 carbohydrates (sugars)
2. lipids (fat)
3.proteins (meat)
4. nucleic acids (DNA, RNA)

sorry I misread your question
here is a useful link, but I'm not sure what are the 4 classes of all organic compounds
http://www.answers.com/topic/organic-compound

Answer 3

I believe they are
1.Hydrocarbons
2.Aromatic
3.Aliphatic
4.Polymers

Not positive if these are the classifications you want though.

EDIT: Go with the above post if you are looking for something hat relates to biology.