Ex: Abduct, calm
My "rules" were:
1. No plurals
2. No obvious loanwords
3. No proper nouns or adjectives based on proper nouns
4. No consulting a dictionary or the Internet, except to check if a word really exists
Here are the sets of letters I couldn't think up words for, unless I break rules 2 or 3:
EDIT: The words I placed in parentheses break rules 2 or 3, or just don't exist in the case of "labcoat". Sorry if that wasn't clear.

fg (afghan)

jk
pq
qr (impossible, right?)
vw
wx
EDIT: wow you guys are quick!
cd - anecdote
kl - duckling
uv - maneuver
Any help here? If you can think of any more words using the 3 difficult sets of letters feel free to comment as well.
EDIT: Someone posted a comment with a bunch of words from a lexicon app, so I'm not going to post LJ user "credit" on the list any more. But if you would like to continue to think up words go ahead :)