Oh my god there are so many- mostly when they are in different compounds but some of them have an awful smell all of their own! Sulfur is a big contender, as is its group-mate tellurium. The worst things i’ve worked with are nitrogen-containing molecules.
Once I was working with a molecule called 3-methyl indole. I was using it in small amounts so I didn’t notice a bad smell, but all my labmates were complaining that it smelled AWFUL in the lab. A few days later we were looking for presents for a friend who just had a baby, and found a baby-gro with the phrase “3-methyl indole happens” written on it. It all became clear, and after a quick google, we found out that I had actually been working with the molecule that gives poo it’s distinct and horrible smell! SO GROSS. I stopped using it.
There are so many awful foul smelling chemicals that really too many to mention and others which may not smell bas but I generally just do not like them! Any nitrogen compound like amines really smell like fish rotting and even some organic acids can be quite disgusting! Although sometimes we can start with the most foul smelling chemicals then create a beautiful scent that might even be used in a perfume! The wonders of Chemistry