Question regarding the difference in vaporization of two like compounds.

Not really sure how to phrase that question without it being a mile long sooo on to the details and explanation.

Ok so I have two compounds of a very similar nature but slightly different.

When compound A is vaporized it burns off clean leaving no residue at all.

When compound B is vaporized it burns off but leaves a small black residue behind.

What could one say about compound B that would be causing these residual resins? Would they be impurities in the compound or could it just be something like the molecular make-up of said compound that disables it from being broken down completely or maybe not enough heat to break all the bonds? I have a somewhat rudimentary understanding of chemistry so my suggestions could be way out in left field for all I know.

If it helps any, here are pictures of the molecular structures of compound A and compound B. From what I can gather , compound A has an extra benzene ring attached, while compound B lacks said ring but has an extra oxygen and hydrogen molecule on the end of it. The thing that I find confusing about this is that compound A is the one burnin off clean, if I had to guess I would have thought the other way around due to the extra carbon associated with it.

hmm this turned out to be a lot longer of a question than I previously anticipated lol

So yeaaaa anyone got any idea what about the molecular structure of compound B that would lead to this residue?