Non Competitive inhibitors are

I) Copper II) Mercury III) Silver IV) Malonate

When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor. e.g., inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure. 

In non-competitive enzyme inhibition , the inhibitor has no structural similarity with the substrate and forms an enzyme inhibitor complex at a point other than it active sites, so that the globular structure of the enzyme gets changed . As a result catalysis cannot takes place.   Ex- Copper , Mercury and Silver .