Can I use trotzdem instead of obwohl? For example:
Trotzdem er krank war, ging er noch zur Arbeit.
Obwohl er krank war, ging er noch zur Arbeit.
Agreeing with thekeyofgb's comment, it is not apparent that they are similar. But in used in their right place, they convey the same effect:
There is a third (at least) possibility trotz+(
According to wiktionary the order you put the sentence in, is also allowed, but it is umgangssprachlich:
I must say that I've never heard the trotzdem in this subjunctional use. The pronunciation remark, added by Emanuel, is that the second syllable should be stressed if trotzdem is intended with this meaning (opposite to [ˈtʀɔʦdeːm], the adverb.)