[toddm]

I am a professional chemist (Ph.D.). After a time, one gets a chemical intuition (as I've heard it called). There are just things that you know or you know where to look and how to filter irrelevant information.

All of that depends on your training and experience. I am not particularly strong in the organic department; however, I am quite expert in areas of physical, aqueous, and computational chemistry. I'm also a geochemist, and have significant lab experience in mostly analytical chemistry. Needless to say, I'm a decent programmer, know a bunch of lab stuff, am quote proficient in linear algebra, and so on. Those main and ancillary skills together give me a pretty good idea of what's going on without having to consult any references.

Resources that I use daily: PubChem, ACS journals, my textbooks, visualization tools, and some software if I'm targeting a certain outcome. IUPAC for naming organics (rarely for me).

Also, I answer questions on the Chemistry Stack Exchange site (not so much these days) which requires a decent amount of digging in order to answer coherently.